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32 results

swapfile.c

Blame
    • Qian Cai's avatar
      a449bf58
      mm/swapfile: fix and annotate various data races · a449bf58
      Qian Cai authored
      swap_info_struct si.highest_bit, si.swap_map[offset] and si.flags could
      be accessed concurrently separately as noticed by KCSAN,
      
      === si.highest_bit ===
      
       write to 0xffff8d5abccdc4d4 of 4 bytes by task 5353 on cpu 24:
        swap_range_alloc+0x81/0x130
        swap_range_alloc at mm/swapfile.c:681
        scan_swap_map_slots+0x371/0xb90
        get_swap_pages+0x39d/0x5c0
        get_swap_page+0xf2/0x524
        add_to_swap+0xe4/0x1c0
        shrink_page_list+0x1795/0x2870
        shrink_inactive_list+0x316/0x880
        shrink_lruvec+0x8dc/0x1380
        shrink_node+0x317/0xd80
        do_try_to_free_pages+0x1f7/0xa10
        try_to_free_pages+0x26c/0x5e0
        __alloc_pages_slowpath+0x458/0x1290
      
       read to 0xffff8d5abccdc4d4 of 4 bytes by task 6672 on cpu 70:
        scan_swap_map_slots+0x4a6/0xb90
        scan_swap_map_slots at mm/swapfile.c:892
        get_swap_pages+0x39d/0x5c0
        get_swap_page+0xf2/0x524
        add_to_swap+0xe4/0x1c0
        shrink_page_list+0x1795/0x2870
        shrink_inactive_list+0x316/0x880
        shrink_lruvec+0x8dc/0x1380
        shrink_node+0x317/0xd80
        do_try_to_free_pages+0x1f7/0xa10
        try_to_free_pages+0x26c/0x5e0
        __alloc_pages_slowpath+0x458/0x1290
      
       Reported by Kernel Concurrency Sanitizer on:
       CPU: 70 PID: 6672 Comm: oom01 Tainted: G        W    L 5.5.0-next-20200205+ #3
       Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 07/10/2019
      
      === si.swap_map[offset] ===
      
       write to 0xffffbc370c29a64c of 1 bytes by task 6856 on cpu 86:
        __swap_entry_free_locked+0x8c/0x100
        __swap_entry_free_locked at mm/swapfile.c:1209 (discriminator 4)
        __swap_entry_free.constprop.20+0x69/0xb0
        free_swap_and_cache+0x53/0xa0
        unmap_page_range+0x7f8/0x1d70
        unmap_single_vma+0xcd/0x170
        unmap_vmas+0x18b/0x220
        exit_mmap+0xee/0x220
        mmput+0x10e/0x270
        do_exit+0x59b/0xf40
        do_group_exit+0x8b/0x180
      
       read to 0xffffbc370c29a64c of 1 bytes by task 6855 on cpu 20:
        _swap_info_get+0x81/0xa0
        _swap_info_get at mm/swapfile.c:1140
        free_swap_and_cache+0x40/0xa0
        unmap_page_range+0x7f8/0x1d70
        unmap_single_vma+0xcd/0x170
        unmap_vmas+0x18b/0x220
        exit_mmap+0xee/0x220
        mmput+0x10e/0x270
        do_exit+0x59b/0xf40
        do_group_exit+0x8b/0x180
      
      === si.flags ===
      
       write to 0xffff956c8fc6c400 of 8 bytes by task 6087 on cpu 23:
        scan_swap_map_slots+0x6fe/0xb50
        scan_swap_map_slots at mm/swapfile.c:887
        get_swap_pages+0x39d/0x5c0
        get_swap_page+0x377/0x524
        add_to_swap+0xe4/0x1c0
        shrink_page_list+0x1795/0x2870
        shrink_inactive_list+0x316/0x880
        shrink_lruvec+0x8dc/0x1380
        shrink_node+0x317/0xd80
        do_try_to_free_pages+0x1f7/0xa10
        try_to_free_pages+0x26c/0x5e0
        __alloc_pages_slowpath+0x458/0x1290
      
       read to 0xffff956c8fc6c400 of 8 bytes by task 6207 on cpu 63:
        _swap_info_get+0x41/0xa0
        __swap_info_get at mm/swapfile.c:1114
        put_swap_page+0x84/0x490
        __remove_mapping+0x384/0x5f0
        shrink_page_list+0xff1/0x2870
        shrink_inactive_list+0x316/0x880
        shrink_lruvec+0x8dc/0x1380
        shrink_node+0x317/0xd80
        do_try_to_free_pages+0x1f7/0xa10
        try_to_free_pages+0x26c/0x5e0
        __alloc_pages_slowpath+0x458/0x1290
      
      The writes are under si->lock but the reads are not. For si.highest_bit
      and si.swap_map[offset], data race could trigger logic bugs, so fix them
      by having WRITE_ONCE() for the writes and READ_ONCE() for the reads
      except those isolated reads where they compare against zero which a data
      race would cause no harm. Thus, annotate them as intentional data races
      using the data_race() macro.
      
      For si.flags, the readers are only interested in a single bit where a
      data race there would cause no issue there.
      
      [cai@lca.pw: add a missing annotation for si->flags in memory.c]
        Link: http://lkml.kernel.org/r/1581612647-5958-1-git-send-email-cai@lca.pw
      
      
      
      Signed-off-by: default avatarQian Cai <cai@lca.pw>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Cc: Marco Elver <elver@google.com>
      Cc: Hugh Dickins <hughd@google.com>
      Link: http://lkml.kernel.org/r/1581095163-12198-1-git-send-email-cai@lca.pw
      
      
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      a449bf58
      History
      mm/swapfile: fix and annotate various data races
      Qian Cai authored
      swap_info_struct si.highest_bit, si.swap_map[offset] and si.flags could
      be accessed concurrently separately as noticed by KCSAN,
      
      === si.highest_bit ===
      
       write to 0xffff8d5abccdc4d4 of 4 bytes by task 5353 on cpu 24:
        swap_range_alloc+0x81/0x130
        swap_range_alloc at mm/swapfile.c:681
        scan_swap_map_slots+0x371/0xb90
        get_swap_pages+0x39d/0x5c0
        get_swap_page+0xf2/0x524
        add_to_swap+0xe4/0x1c0
        shrink_page_list+0x1795/0x2870
        shrink_inactive_list+0x316/0x880
        shrink_lruvec+0x8dc/0x1380
        shrink_node+0x317/0xd80
        do_try_to_free_pages+0x1f7/0xa10
        try_to_free_pages+0x26c/0x5e0
        __alloc_pages_slowpath+0x458/0x1290
      
       read to 0xffff8d5abccdc4d4 of 4 bytes by task 6672 on cpu 70:
        scan_swap_map_slots+0x4a6/0xb90
        scan_swap_map_slots at mm/swapfile.c:892
        get_swap_pages+0x39d/0x5c0
        get_swap_page+0xf2/0x524
        add_to_swap+0xe4/0x1c0
        shrink_page_list+0x1795/0x2870
        shrink_inactive_list+0x316/0x880
        shrink_lruvec+0x8dc/0x1380
        shrink_node+0x317/0xd80
        do_try_to_free_pages+0x1f7/0xa10
        try_to_free_pages+0x26c/0x5e0
        __alloc_pages_slowpath+0x458/0x1290
      
       Reported by Kernel Concurrency Sanitizer on:
       CPU: 70 PID: 6672 Comm: oom01 Tainted: G        W    L 5.5.0-next-20200205+ #3
       Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 07/10/2019
      
      === si.swap_map[offset] ===
      
       write to 0xffffbc370c29a64c of 1 bytes by task 6856 on cpu 86:
        __swap_entry_free_locked+0x8c/0x100
        __swap_entry_free_locked at mm/swapfile.c:1209 (discriminator 4)
        __swap_entry_free.constprop.20+0x69/0xb0
        free_swap_and_cache+0x53/0xa0
        unmap_page_range+0x7f8/0x1d70
        unmap_single_vma+0xcd/0x170
        unmap_vmas+0x18b/0x220
        exit_mmap+0xee/0x220
        mmput+0x10e/0x270
        do_exit+0x59b/0xf40
        do_group_exit+0x8b/0x180
      
       read to 0xffffbc370c29a64c of 1 bytes by task 6855 on cpu 20:
        _swap_info_get+0x81/0xa0
        _swap_info_get at mm/swapfile.c:1140
        free_swap_and_cache+0x40/0xa0
        unmap_page_range+0x7f8/0x1d70
        unmap_single_vma+0xcd/0x170
        unmap_vmas+0x18b/0x220
        exit_mmap+0xee/0x220
        mmput+0x10e/0x270
        do_exit+0x59b/0xf40
        do_group_exit+0x8b/0x180
      
      === si.flags ===
      
       write to 0xffff956c8fc6c400 of 8 bytes by task 6087 on cpu 23:
        scan_swap_map_slots+0x6fe/0xb50
        scan_swap_map_slots at mm/swapfile.c:887
        get_swap_pages+0x39d/0x5c0
        get_swap_page+0x377/0x524
        add_to_swap+0xe4/0x1c0
        shrink_page_list+0x1795/0x2870
        shrink_inactive_list+0x316/0x880
        shrink_lruvec+0x8dc/0x1380
        shrink_node+0x317/0xd80
        do_try_to_free_pages+0x1f7/0xa10
        try_to_free_pages+0x26c/0x5e0
        __alloc_pages_slowpath+0x458/0x1290
      
       read to 0xffff956c8fc6c400 of 8 bytes by task 6207 on cpu 63:
        _swap_info_get+0x41/0xa0
        __swap_info_get at mm/swapfile.c:1114
        put_swap_page+0x84/0x490
        __remove_mapping+0x384/0x5f0
        shrink_page_list+0xff1/0x2870
        shrink_inactive_list+0x316/0x880
        shrink_lruvec+0x8dc/0x1380
        shrink_node+0x317/0xd80
        do_try_to_free_pages+0x1f7/0xa10
        try_to_free_pages+0x26c/0x5e0
        __alloc_pages_slowpath+0x458/0x1290
      
      The writes are under si->lock but the reads are not. For si.highest_bit
      and si.swap_map[offset], data race could trigger logic bugs, so fix them
      by having WRITE_ONCE() for the writes and READ_ONCE() for the reads
      except those isolated reads where they compare against zero which a data
      race would cause no harm. Thus, annotate them as intentional data races
      using the data_race() macro.
      
      For si.flags, the readers are only interested in a single bit where a
      data race there would cause no issue there.
      
      [cai@lca.pw: add a missing annotation for si->flags in memory.c]
        Link: http://lkml.kernel.org/r/1581612647-5958-1-git-send-email-cai@lca.pw
      
      
      
      Signed-off-by: default avatarQian Cai <cai@lca.pw>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Cc: Marco Elver <elver@google.com>
      Cc: Hugh Dickins <hughd@google.com>
      Link: http://lkml.kernel.org/r/1581095163-12198-1-git-send-email-cai@lca.pw
      
      
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    cpu.c 60.48 KiB
    /* CPU control.
     * (C) 2001, 2002, 2003, 2004 Rusty Russell
     *
     * This code is licenced under the GPL.
     */
    #include <linux/proc_fs.h>
    #include <linux/smp.h>
    #include <linux/init.h>
    #include <linux/notifier.h>
    #include <linux/sched/signal.h>
    #include <linux/sched/hotplug.h>
    #include <linux/sched/isolation.h>
    #include <linux/sched/task.h>
    #include <linux/sched/smt.h>
    #include <linux/unistd.h>
    #include <linux/cpu.h>
    #include <linux/oom.h>
    #include <linux/rcupdate.h>
    #include <linux/export.h>
    #include <linux/bug.h>
    #include <linux/kthread.h>
    #include <linux/stop_machine.h>
    #include <linux/mutex.h>
    #include <linux/gfp.h>
    #include <linux/suspend.h>
    #include <linux/lockdep.h>
    #include <linux/tick.h>
    #include <linux/irq.h>
    #include <linux/nmi.h>
    #include <linux/smpboot.h>
    #include <linux/relay.h>
    #include <linux/slab.h>
    #include <linux/percpu-rwsem.h>
    
    #include <trace/events/power.h>
    #define CREATE_TRACE_POINTS
    #include <trace/events/cpuhp.h>
    
    #include "smpboot.h"
    
    /**
     * cpuhp_cpu_state - Per cpu hotplug state storage
     * @state:	The current cpu state
     * @target:	The target state
     * @thread:	Pointer to the hotplug thread
     * @should_run:	Thread should execute
     * @rollback:	Perform a rollback
     * @single:	Single callback invocation
     * @bringup:	Single callback bringup or teardown selector
     * @cb_state:	The state for a single callback (install/uninstall)
     * @result:	Result of the operation
     * @done_up:	Signal completion to the issuer of the task for cpu-up
     * @done_down:	Signal completion to the issuer of the task for cpu-down
     */
    struct cpuhp_cpu_state {
    	enum cpuhp_state	state;
    	enum cpuhp_state	target;
    	enum cpuhp_state	fail;
    #ifdef CONFIG_SMP
    	struct task_struct	*thread;
    	bool			should_run;
    	bool			rollback;
    	bool			single;
    	bool			bringup;
    	struct hlist_node	*node;
    	struct hlist_node	*last;
    	enum cpuhp_state	cb_state;
    	int			result;
    	struct completion	done_up;
    	struct completion	done_down;
    #endif
    };
    
    static DEFINE_PER_CPU(struct cpuhp_cpu_state, cpuhp_state) = {
    	.fail = CPUHP_INVALID,
    };
    
    #ifdef CONFIG_SMP
    cpumask_t cpus_booted_once_mask;
    #endif
    
    #if defined(CONFIG_LOCKDEP) && defined(CONFIG_SMP)
    static struct lockdep_map cpuhp_state_up_map =
    	STATIC_LOCKDEP_MAP_INIT("cpuhp_state-up", &cpuhp_state_up_map);
    static struct lockdep_map cpuhp_state_down_map =
    	STATIC_LOCKDEP_MAP_INIT("cpuhp_state-down", &cpuhp_state_down_map);
    
    
    static inline void cpuhp_lock_acquire(bool bringup)
    {
    	lock_map_acquire(bringup ? &cpuhp_state_up_map : &cpuhp_state_down_map);
    }
    
    static inline void cpuhp_lock_release(bool bringup)
    {
    	lock_map_release(bringup ? &cpuhp_state_up_map : &cpuhp_state_down_map);
    }
    #else
    
    static inline void cpuhp_lock_acquire(bool bringup) { }
    static inline void cpuhp_lock_release(bool bringup) { }
    
    #endif
    
    /**
     * cpuhp_step - Hotplug state machine step
     * @name:	Name of the step
     * @startup:	Startup function of the step
     * @teardown:	Teardown function of the step
     * @cant_stop:	Bringup/teardown can't be stopped at this step
     */
    struct cpuhp_step {
    	const char		*name;
    	union {
    		int		(*single)(unsigned int cpu);
    		int		(*multi)(unsigned int cpu,
    					 struct hlist_node *node);
    	} startup;
    	union {
    		int		(*single)(unsigned int cpu);
    		int		(*multi)(unsigned int cpu,
    					 struct hlist_node *node);
    	} teardown;
    	struct hlist_head	list;
    	bool			cant_stop;
    	bool			multi_instance;
    };
    
    static DEFINE_MUTEX(cpuhp_state_mutex);
    static struct cpuhp_step cpuhp_hp_states[];
    
    static struct cpuhp_step *cpuhp_get_step(enum cpuhp_state state)
    {
    	return cpuhp_hp_states + state;
    }
    
    /**
     * cpuhp_invoke_callback _ Invoke the callbacks for a given state
     * @cpu:	The cpu for which the callback should be invoked
     * @state:	The state to do callbacks for
     * @bringup:	True if the bringup callback should be invoked
     * @node:	For multi-instance, do a single entry callback for install/remove
     * @lastp:	For multi-instance rollback, remember how far we got
     *
     * Called from cpu hotplug and from the state register machinery.
     */
    static int cpuhp_invoke_callback(unsigned int cpu, enum cpuhp_state state,
    				 bool bringup, struct hlist_node *node,
    				 struct hlist_node **lastp)
    {
    	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
    	struct cpuhp_step *step = cpuhp_get_step(state);
    	int (*cbm)(unsigned int cpu, struct hlist_node *node);
    	int (*cb)(unsigned int cpu);
    	int ret, cnt;
    
    	if (st->fail == state) {
    		st->fail = CPUHP_INVALID;
    
    		if (!(bringup ? step->startup.single : step->teardown.single))
    			return 0;
    
    		return -EAGAIN;
    	}
    
    	if (!step->multi_instance) {
    		WARN_ON_ONCE(lastp && *lastp);
    		cb = bringup ? step->startup.single : step->teardown.single;
    		if (!cb)
    			return 0;
    		trace_cpuhp_enter(cpu, st->target, state, cb);
    		ret = cb(cpu);
    		trace_cpuhp_exit(cpu, st->state, state, ret);
    		return ret;
    	}
    	cbm = bringup ? step->startup.multi : step->teardown.multi;
    	if (!cbm)
    		return 0;
    
    	/* Single invocation for instance add/remove */
    	if (node) {
    		WARN_ON_ONCE(lastp && *lastp);
    		trace_cpuhp_multi_enter(cpu, st->target, state, cbm, node);
    		ret = cbm(cpu, node);
    		trace_cpuhp_exit(cpu, st->state, state, ret);
    		return ret;
    	}
    
    	/* State transition. Invoke on all instances */
    	cnt = 0;
    	hlist_for_each(node, &step->list) {
    		if (lastp && node == *lastp)
    			break;
    
    		trace_cpuhp_multi_enter(cpu, st->target, state, cbm, node);
    		ret = cbm(cpu, node);
    		trace_cpuhp_exit(cpu, st->state, state, ret);
    		if (ret) {
    			if (!lastp)
    				goto err;
    
    			*lastp = node;
    			return ret;
    		}
    		cnt++;
    	}
    	if (lastp)
    		*lastp = NULL;
    	return 0;
    err:
    	/* Rollback the instances if one failed */
    	cbm = !bringup ? step->startup.multi : step->teardown.multi;
    	if (!cbm)
    		return ret;
    
    	hlist_for_each(node, &step->list) {
    		if (!cnt--)
    			break;
    
    		trace_cpuhp_multi_enter(cpu, st->target, state, cbm, node);
    		ret = cbm(cpu, node);
    		trace_cpuhp_exit(cpu, st->state, state, ret);
    		/*
    		 * Rollback must not fail,
    		 */
    		WARN_ON_ONCE(ret);
    	}
    	return ret;
    }
    
    #ifdef CONFIG_SMP
    static bool cpuhp_is_ap_state(enum cpuhp_state state)
    {
    	/*
    	 * The extra check for CPUHP_TEARDOWN_CPU is only for documentation
    	 * purposes as that state is handled explicitly in cpu_down.
    	 */
    	return state > CPUHP_BRINGUP_CPU && state != CPUHP_TEARDOWN_CPU;
    }
    
    static inline void wait_for_ap_thread(struct cpuhp_cpu_state *st, bool bringup)
    {
    	struct completion *done = bringup ? &st->done_up : &st->done_down;
    	wait_for_completion(done);
    }
    
    static inline void complete_ap_thread(struct cpuhp_cpu_state *st, bool bringup)
    {
    	struct completion *done = bringup ? &st->done_up : &st->done_down;
    	complete(done);
    }
    
    /*
     * The former STARTING/DYING states, ran with IRQs disabled and must not fail.
     */
    static bool cpuhp_is_atomic_state(enum cpuhp_state state)
    {
    	return CPUHP_AP_IDLE_DEAD <= state && state < CPUHP_AP_ONLINE;
    }
    
    /* Serializes the updates to cpu_online_mask, cpu_present_mask */
    static DEFINE_MUTEX(cpu_add_remove_lock);
    bool cpuhp_tasks_frozen;
    EXPORT_SYMBOL_GPL(cpuhp_tasks_frozen);
    
    /*
     * The following two APIs (cpu_maps_update_begin/done) must be used when
     * attempting to serialize the updates to cpu_online_mask & cpu_present_mask.
     */
    void cpu_maps_update_begin(void)
    {
    	mutex_lock(&cpu_add_remove_lock);
    }
    
    void cpu_maps_update_done(void)
    {
    	mutex_unlock(&cpu_add_remove_lock);
    }
    
    /*
     * If set, cpu_up and cpu_down will return -EBUSY and do nothing.
     * Should always be manipulated under cpu_add_remove_lock
     */
    static int cpu_hotplug_disabled;
    
    #ifdef CONFIG_HOTPLUG_CPU
    
    DEFINE_STATIC_PERCPU_RWSEM(cpu_hotplug_lock);
    
    void cpus_read_lock(void)
    {
    	percpu_down_read(&cpu_hotplug_lock);
    }
    EXPORT_SYMBOL_GPL(cpus_read_lock);
    
    int cpus_read_trylock(void)
    {
    	return percpu_down_read_trylock(&cpu_hotplug_lock);
    }
    EXPORT_SYMBOL_GPL(cpus_read_trylock);
    
    void cpus_read_unlock(void)
    {
    	percpu_up_read(&cpu_hotplug_lock);
    }
    EXPORT_SYMBOL_GPL(cpus_read_unlock);
    
    void cpus_write_lock(void)
    {
    	percpu_down_write(&cpu_hotplug_lock);
    }
    
    void cpus_write_unlock(void)
    {
    	percpu_up_write(&cpu_hotplug_lock);
    }
    
    void lockdep_assert_cpus_held(void)
    {
    	/*
    	 * We can't have hotplug operations before userspace starts running,
    	 * and some init codepaths will knowingly not take the hotplug lock.
    	 * This is all valid, so mute lockdep until it makes sense to report
    	 * unheld locks.
    	 */
    	if (system_state < SYSTEM_RUNNING)
    		return;
    
    	percpu_rwsem_assert_held(&cpu_hotplug_lock);
    }
    
    static void lockdep_acquire_cpus_lock(void)
    {
    	rwsem_acquire(&cpu_hotplug_lock.rw_sem.dep_map, 0, 0, _THIS_IP_);
    }
    
    static void lockdep_release_cpus_lock(void)
    {
    	rwsem_release(&cpu_hotplug_lock.rw_sem.dep_map, _THIS_IP_);
    }
    
    /*
     * Wait for currently running CPU hotplug operations to complete (if any) and
     * disable future CPU hotplug (from sysfs). The 'cpu_add_remove_lock' protects
     * the 'cpu_hotplug_disabled' flag. The same lock is also acquired by the
     * hotplug path before performing hotplug operations. So acquiring that lock
     * guarantees mutual exclusion from any currently running hotplug operations.
     */
    void cpu_hotplug_disable(void)
    {
    	cpu_maps_update_begin();
    	cpu_hotplug_disabled++;
    	cpu_maps_update_done();
    }
    EXPORT_SYMBOL_GPL(cpu_hotplug_disable);
    
    static void __cpu_hotplug_enable(void)
    {
    	if (WARN_ONCE(!cpu_hotplug_disabled, "Unbalanced cpu hotplug enable\n"))
    		return;
    	cpu_hotplug_disabled--;
    }
    
    void cpu_hotplug_enable(void)
    {
    	cpu_maps_update_begin();
    	__cpu_hotplug_enable();
    	cpu_maps_update_done();
    }
    EXPORT_SYMBOL_GPL(cpu_hotplug_enable);
    
    #else
    
    static void lockdep_acquire_cpus_lock(void)
    {
    }
    
    static void lockdep_release_cpus_lock(void)
    {
    }
    
    #endif	/* CONFIG_HOTPLUG_CPU */
    
    /*
     * Architectures that need SMT-specific errata handling during SMT hotplug
     * should override this.
     */
    void __weak arch_smt_update(void) { }
    
    #ifdef CONFIG_HOTPLUG_SMT
    enum cpuhp_smt_control cpu_smt_control __read_mostly = CPU_SMT_ENABLED;
    
    void __init cpu_smt_disable(bool force)
    {
    	if (!cpu_smt_possible())
    		return;
    
    	if (force) {
    		pr_info("SMT: Force disabled\n");
    		cpu_smt_control = CPU_SMT_FORCE_DISABLED;
    	} else {
    		pr_info("SMT: disabled\n");
    		cpu_smt_control = CPU_SMT_DISABLED;
    	}
    }
    
    /*
     * The decision whether SMT is supported can only be done after the full
     * CPU identification. Called from architecture code.
     */
    void __init cpu_smt_check_topology(void)
    {
    	if (!topology_smt_supported())
    		cpu_smt_control = CPU_SMT_NOT_SUPPORTED;
    }
    
    static int __init smt_cmdline_disable(char *str)
    {
    	cpu_smt_disable(str && !strcmp(str, "force"));
    	return 0;
    }
    early_param("nosmt", smt_cmdline_disable);
    
    static inline bool cpu_smt_allowed(unsigned int cpu)
    {
    	if (cpu_smt_control == CPU_SMT_ENABLED)
    		return true;
    
    	if (topology_is_primary_thread(cpu))
    		return true;
    
    	/*
    	 * On x86 it's required to boot all logical CPUs at least once so
    	 * that the init code can get a chance to set CR4.MCE on each
    	 * CPU. Otherwise, a broadacasted MCE observing CR4.MCE=0b on any
    	 * core will shutdown the machine.
    	 */
    	return !cpumask_test_cpu(cpu, &cpus_booted_once_mask);
    }
    
    /* Returns true if SMT is not supported of forcefully (irreversibly) disabled */
    bool cpu_smt_possible(void)
    {
    	return cpu_smt_control != CPU_SMT_FORCE_DISABLED &&
    		cpu_smt_control != CPU_SMT_NOT_SUPPORTED;
    }
    EXPORT_SYMBOL_GPL(cpu_smt_possible);
    #else
    static inline bool cpu_smt_allowed(unsigned int cpu) { return true; }
    #endif
    
    static inline enum cpuhp_state
    cpuhp_set_state(struct cpuhp_cpu_state *st, enum cpuhp_state target)
    {
    	enum cpuhp_state prev_state = st->state;
    
    	st->rollback = false;
    	st->last = NULL;
    
    	st->target = target;
    	st->single = false;
    	st->bringup = st->state < target;
    
    	return prev_state;
    }
    
    static inline void
    cpuhp_reset_state(struct cpuhp_cpu_state *st, enum cpuhp_state prev_state)
    {
    	st->rollback = true;
    
    	/*
    	 * If we have st->last we need to undo partial multi_instance of this
    	 * state first. Otherwise start undo at the previous state.
    	 */
    	if (!st->last) {
    		if (st->bringup)
    			st->state--;
    		else
    			st->state++;
    	}
    
    	st->target = prev_state;
    	st->bringup = !st->bringup;
    }
    
    /* Regular hotplug invocation of the AP hotplug thread */
    static void __cpuhp_kick_ap(struct cpuhp_cpu_state *st)
    {
    	if (!st->single && st->state == st->target)
    		return;
    
    	st->result = 0;
    	/*
    	 * Make sure the above stores are visible before should_run becomes
    	 * true. Paired with the mb() above in cpuhp_thread_fun()
    	 */
    	smp_mb();
    	st->should_run = true;
    	wake_up_process(st->thread);
    	wait_for_ap_thread(st, st->bringup);
    }
    
    static int cpuhp_kick_ap(struct cpuhp_cpu_state *st, enum cpuhp_state target)
    {
    	enum cpuhp_state prev_state;
    	int ret;
    
    	prev_state = cpuhp_set_state(st, target);
    	__cpuhp_kick_ap(st);
    	if ((ret = st->result)) {
    		cpuhp_reset_state(st, prev_state);
    		__cpuhp_kick_ap(st);
    	}
    
    	return ret;
    }
    
    static int bringup_wait_for_ap(unsigned int cpu)
    {
    	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
    
    	/* Wait for the CPU to reach CPUHP_AP_ONLINE_IDLE */
    	wait_for_ap_thread(st, true);
    	if (WARN_ON_ONCE((!cpu_online(cpu))))
    		return -ECANCELED;
    
    	/* Unpark the hotplug thread of the target cpu */
    	kthread_unpark(st->thread);
    
    	/*
    	 * SMT soft disabling on X86 requires to bring the CPU out of the
    	 * BIOS 'wait for SIPI' state in order to set the CR4.MCE bit.  The
    	 * CPU marked itself as booted_once in notify_cpu_starting() so the
    	 * cpu_smt_allowed() check will now return false if this is not the
    	 * primary sibling.
    	 */
    	if (!cpu_smt_allowed(cpu))
    		return -ECANCELED;
    
    	if (st->target <= CPUHP_AP_ONLINE_IDLE)
    		return 0;
    
    	return cpuhp_kick_ap(st, st->target);
    }
    
    static int bringup_cpu(unsigned int cpu)
    {
    	struct task_struct *idle = idle_thread_get(cpu);
    	int ret;
    
    	/*
    	 * Some architectures have to walk the irq descriptors to
    	 * setup the vector space for the cpu which comes online.
    	 * Prevent irq alloc/free across the bringup.
    	 */
    	irq_lock_sparse();
    
    	/* Arch-specific enabling code. */
    	ret = __cpu_up(cpu, idle);
    	irq_unlock_sparse();
    	if (ret)
    		return ret;
    	return bringup_wait_for_ap(cpu);
    }
    
    /*
     * Hotplug state machine related functions
     */
    
    static void undo_cpu_up(unsigned int cpu, struct cpuhp_cpu_state *st)
    {
    	for (st->state--; st->state > st->target; st->state--)
    		cpuhp_invoke_callback(cpu, st->state, false, NULL, NULL);
    }
    
    static inline bool can_rollback_cpu(struct cpuhp_cpu_state *st)
    {
    	if (IS_ENABLED(CONFIG_HOTPLUG_CPU))
    		return true;
    	/*
    	 * When CPU hotplug is disabled, then taking the CPU down is not
    	 * possible because takedown_cpu() and the architecture and
    	 * subsystem specific mechanisms are not available. So the CPU
    	 * which would be completely unplugged again needs to stay around
    	 * in the current state.
    	 */
    	return st->state <= CPUHP_BRINGUP_CPU;
    }
    
    static int cpuhp_up_callbacks(unsigned int cpu, struct cpuhp_cpu_state *st,
    			      enum cpuhp_state target)
    {
    	enum cpuhp_state prev_state = st->state;
    	int ret = 0;
    
    	while (st->state < target) {
    		st->state++;
    		ret = cpuhp_invoke_callback(cpu, st->state, true, NULL, NULL);
    		if (ret) {
    			if (can_rollback_cpu(st)) {
    				st->target = prev_state;
    				undo_cpu_up(cpu, st);
    			}
    			break;
    		}
    	}
    	return ret;
    }
    
    /*
     * The cpu hotplug threads manage the bringup and teardown of the cpus
     */
    static void cpuhp_create(unsigned int cpu)
    {
    	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
    
    	init_completion(&st->done_up);
    	init_completion(&st->done_down);
    }
    
    static int cpuhp_should_run(unsigned int cpu)
    {
    	struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
    
    	return st->should_run;
    }
    
    /*
     * Execute teardown/startup callbacks on the plugged cpu. Also used to invoke
     * callbacks when a state gets [un]installed at runtime.
     *
     * Each invocation of this function by the smpboot thread does a single AP
     * state callback.
     *
     * It has 3 modes of operation:
     *  - single: runs st->cb_state
     *  - up:     runs ++st->state, while st->state < st->target
     *  - down:   runs st->state--, while st->state > st->target
     *
     * When complete or on error, should_run is cleared and the completion is fired.
     */
    static void cpuhp_thread_fun(unsigned int cpu)
    {
    	struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
    	bool bringup = st->bringup;
    	enum cpuhp_state state;
    
    	if (WARN_ON_ONCE(!st->should_run))
    		return;
    
    	/*
    	 * ACQUIRE for the cpuhp_should_run() load of ->should_run. Ensures
    	 * that if we see ->should_run we also see the rest of the state.
    	 */
    	smp_mb();
    
    	/*
    	 * The BP holds the hotplug lock, but we're now running on the AP,
    	 * ensure that anybody asserting the lock is held, will actually find
    	 * it so.
    	 */
    	lockdep_acquire_cpus_lock();
    	cpuhp_lock_acquire(bringup);
    
    	if (st->single) {
    		state = st->cb_state;
    		st->should_run = false;
    	} else {
    		if (bringup) {
    			st->state++;
    			state = st->state;
    			st->should_run = (st->state < st->target);
    			WARN_ON_ONCE(st->state > st->target);
    		} else {
    			state = st->state;
    			st->state--;
    			st->should_run = (st->state > st->target);
    			WARN_ON_ONCE(st->state < st->target);
    		}
    	}
    
    	WARN_ON_ONCE(!cpuhp_is_ap_state(state));
    
    	if (cpuhp_is_atomic_state(state)) {
    		local_irq_disable();
    		st->result = cpuhp_invoke_callback(cpu, state, bringup, st->node, &st->last);
    		local_irq_enable();
    
    		/*
    		 * STARTING/DYING must not fail!
    		 */
    		WARN_ON_ONCE(st->result);
    	} else {
    		st->result = cpuhp_invoke_callback(cpu, state, bringup, st->node, &st->last);
    	}
    
    	if (st->result) {
    		/*
    		 * If we fail on a rollback, we're up a creek without no
    		 * paddle, no way forward, no way back. We loose, thanks for
    		 * playing.
    		 */
    		WARN_ON_ONCE(st->rollback);
    		st->should_run = false;
    	}
    
    	cpuhp_lock_release(bringup);
    	lockdep_release_cpus_lock();
    
    	if (!st->should_run)
    		complete_ap_thread(st, bringup);
    }
    
    /* Invoke a single callback on a remote cpu */
    static int
    cpuhp_invoke_ap_callback(int cpu, enum cpuhp_state state, bool bringup,
    			 struct hlist_node *node)
    {
    	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
    	int ret;
    
    	if (!cpu_online(cpu))
    		return 0;
    
    	cpuhp_lock_acquire(false);
    	cpuhp_lock_release(false);
    
    	cpuhp_lock_acquire(true);
    	cpuhp_lock_release(true);
    
    	/*
    	 * If we are up and running, use the hotplug thread. For early calls
    	 * we invoke the thread function directly.
    	 */
    	if (!st->thread)
    		return cpuhp_invoke_callback(cpu, state, bringup, node, NULL);
    
    	st->rollback = false;
    	st->last = NULL;
    
    	st->node = node;
    	st->bringup = bringup;
    	st->cb_state = state;
    	st->single = true;
    
    	__cpuhp_kick_ap(st);
    
    	/*
    	 * If we failed and did a partial, do a rollback.
    	 */
    	if ((ret = st->result) && st->last) {
    		st->rollback = true;
    		st->bringup = !bringup;
    
    		__cpuhp_kick_ap(st);
    	}
    
    	/*
    	 * Clean up the leftovers so the next hotplug operation wont use stale
    	 * data.
    	 */
    	st->node = st->last = NULL;
    	return ret;
    }
    
    static int cpuhp_kick_ap_work(unsigned int cpu)
    {
    	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
    	enum cpuhp_state prev_state = st->state;
    	int ret;
    
    	cpuhp_lock_acquire(false);
    	cpuhp_lock_release(false);
    
    	cpuhp_lock_acquire(true);
    	cpuhp_lock_release(true);
    
    	trace_cpuhp_enter(cpu, st->target, prev_state, cpuhp_kick_ap_work);
    	ret = cpuhp_kick_ap(st, st->target);
    	trace_cpuhp_exit(cpu, st->state, prev_state, ret);
    
    	return ret;
    }
    
    static struct smp_hotplug_thread cpuhp_threads = {
    	.store			= &cpuhp_state.thread,
    	.create			= &cpuhp_create,
    	.thread_should_run	= cpuhp_should_run,
    	.thread_fn		= cpuhp_thread_fun,
    	.thread_comm		= "cpuhp/%u",
    	.selfparking		= true,
    };
    
    void __init cpuhp_threads_init(void)
    {
    	BUG_ON(smpboot_register_percpu_thread(&cpuhp_threads));
    	kthread_unpark(this_cpu_read(cpuhp_state.thread));
    }
    
    #ifdef CONFIG_HOTPLUG_CPU
    /**
     * clear_tasks_mm_cpumask - Safely clear tasks' mm_cpumask for a CPU
     * @cpu: a CPU id
     *
     * This function walks all processes, finds a valid mm struct for each one and
     * then clears a corresponding bit in mm's cpumask.  While this all sounds
     * trivial, there are various non-obvious corner cases, which this function
     * tries to solve in a safe manner.
     *
     * Also note that the function uses a somewhat relaxed locking scheme, so it may
     * be called only for an already offlined CPU.
     */
    void clear_tasks_mm_cpumask(int cpu)
    {
    	struct task_struct *p;
    
    	/*
    	 * This function is called after the cpu is taken down and marked
    	 * offline, so its not like new tasks will ever get this cpu set in
    	 * their mm mask. -- Peter Zijlstra
    	 * Thus, we may use rcu_read_lock() here, instead of grabbing
    	 * full-fledged tasklist_lock.
    	 */
    	WARN_ON(cpu_online(cpu));
    	rcu_read_lock();
    	for_each_process(p) {
    		struct task_struct *t;
    
    		/*
    		 * Main thread might exit, but other threads may still have
    		 * a valid mm. Find one.
    		 */
    		t = find_lock_task_mm(p);
    		if (!t)
    			continue;
    		cpumask_clear_cpu(cpu, mm_cpumask(t->mm));
    		task_unlock(t);
    	}
    	rcu_read_unlock();
    }
    
    /* Take this CPU down. */
    static int take_cpu_down(void *_param)
    {
    	struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
    	enum cpuhp_state target = max((int)st->target, CPUHP_AP_OFFLINE);
    	int err, cpu = smp_processor_id();
    	int ret;
    
    	/* Ensure this CPU doesn't handle any more interrupts. */
    	err = __cpu_disable();
    	if (err < 0)
    		return err;
    
    	/*
    	 * We get here while we are in CPUHP_TEARDOWN_CPU state and we must not
    	 * do this step again.
    	 */
    	WARN_ON(st->state != CPUHP_TEARDOWN_CPU);
    	st->state--;
    	/* Invoke the former CPU_DYING callbacks */
    	for (; st->state > target; st->state--) {
    		ret = cpuhp_invoke_callback(cpu, st->state, false, NULL, NULL);
    		/*
    		 * DYING must not fail!
    		 */
    		WARN_ON_ONCE(ret);
    	}
    
    	/* Give up timekeeping duties */
    	tick_handover_do_timer();
    	/* Remove CPU from timer broadcasting */
    	tick_offline_cpu(cpu);
    	/* Park the stopper thread */
    	stop_machine_park(cpu);
    	return 0;
    }
    
    static int takedown_cpu(unsigned int cpu)
    {
    	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
    	int err;
    
    	/* Park the smpboot threads */
    	kthread_park(per_cpu_ptr(&cpuhp_state, cpu)->thread);
    
    	/*
    	 * Prevent irq alloc/free while the dying cpu reorganizes the
    	 * interrupt affinities.
    	 */
    	irq_lock_sparse();
    
    	/*
    	 * So now all preempt/rcu users must observe !cpu_active().
    	 */
    	err = stop_machine_cpuslocked(take_cpu_down, NULL, cpumask_of(cpu));
    	if (err) {
    		/* CPU refused to die */
    		irq_unlock_sparse();
    		/* Unpark the hotplug thread so we can rollback there */
    		kthread_unpark(per_cpu_ptr(&cpuhp_state, cpu)->thread);
    		return err;
    	}
    	BUG_ON(cpu_online(cpu));
    
    	/*
    	 * The teardown callback for CPUHP_AP_SCHED_STARTING will have removed
    	 * all runnable tasks from the CPU, there's only the idle task left now
    	 * that the migration thread is done doing the stop_machine thing.
    	 *
    	 * Wait for the stop thread to go away.
    	 */
    	wait_for_ap_thread(st, false);
    	BUG_ON(st->state != CPUHP_AP_IDLE_DEAD);
    
    	/* Interrupts are moved away from the dying cpu, reenable alloc/free */
    	irq_unlock_sparse();
    
    	hotplug_cpu__broadcast_tick_pull(cpu);
    	/* This actually kills the CPU. */
    	__cpu_die(cpu);
    
    	tick_cleanup_dead_cpu(cpu);
    	rcutree_migrate_callbacks(cpu);
    	return 0;
    }
    
    static void cpuhp_complete_idle_dead(void *arg)
    {
    	struct cpuhp_cpu_state *st = arg;
    
    	complete_ap_thread(st, false);
    }
    
    void cpuhp_report_idle_dead(void)
    {
    	struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
    
    	BUG_ON(st->state != CPUHP_AP_OFFLINE);
    	rcu_report_dead(smp_processor_id());
    	st->state = CPUHP_AP_IDLE_DEAD;
    	/*
    	 * We cannot call complete after rcu_report_dead() so we delegate it
    	 * to an online cpu.
    	 */
    	smp_call_function_single(cpumask_first(cpu_online_mask),
    				 cpuhp_complete_idle_dead, st, 0);
    }
    
    static void undo_cpu_down(unsigned int cpu, struct cpuhp_cpu_state *st)
    {
    	for (st->state++; st->state < st->target; st->state++)
    		cpuhp_invoke_callback(cpu, st->state, true, NULL, NULL);
    }
    
    static int cpuhp_down_callbacks(unsigned int cpu, struct cpuhp_cpu_state *st,
    				enum cpuhp_state target)
    {
    	enum cpuhp_state prev_state = st->state;
    	int ret = 0;
    
    	for (; st->state > target; st->state--) {
    		ret = cpuhp_invoke_callback(cpu, st->state, false, NULL, NULL);
    		if (ret) {
    			st->target = prev_state;
    			if (st->state < prev_state)
    				undo_cpu_down(cpu, st);
    			break;
    		}
    	}
    	return ret;
    }
    
    /* Requires cpu_add_remove_lock to be held */
    static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
    			   enum cpuhp_state target)
    {
    	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
    	int prev_state, ret = 0;
    
    	if (num_online_cpus() == 1)
    		return -EBUSY;
    
    	if (!cpu_present(cpu))
    		return -EINVAL;
    
    	cpus_write_lock();
    
    	cpuhp_tasks_frozen = tasks_frozen;
    
    	prev_state = cpuhp_set_state(st, target);
    	/*
    	 * If the current CPU state is in the range of the AP hotplug thread,
    	 * then we need to kick the thread.
    	 */
    	if (st->state > CPUHP_TEARDOWN_CPU) {
    		st->target = max((int)target, CPUHP_TEARDOWN_CPU);
    		ret = cpuhp_kick_ap_work(cpu);
    		/*
    		 * The AP side has done the error rollback already. Just
    		 * return the error code..
    		 */
    		if (ret)
    			goto out;
    
    		/*
    		 * We might have stopped still in the range of the AP hotplug
    		 * thread. Nothing to do anymore.
    		 */
    		if (st->state > CPUHP_TEARDOWN_CPU)
    			goto out;
    
    		st->target = target;
    	}
    	/*
    	 * The AP brought itself down to CPUHP_TEARDOWN_CPU. So we need
    	 * to do the further cleanups.
    	 */
    	ret = cpuhp_down_callbacks(cpu, st, target);
    	if (ret && st->state == CPUHP_TEARDOWN_CPU && st->state < prev_state) {
    		cpuhp_reset_state(st, prev_state);
    		__cpuhp_kick_ap(st);
    	}
    
    out:
    	cpus_write_unlock();
    	/*
    	 * Do post unplug cleanup. This is still protected against
    	 * concurrent CPU hotplug via cpu_add_remove_lock.
    	 */
    	lockup_detector_cleanup();
    	arch_smt_update();
    	return ret;
    }
    
    static int cpu_down_maps_locked(unsigned int cpu, enum cpuhp_state target)
    {
    	if (cpu_hotplug_disabled)
    		return -EBUSY;
    	return _cpu_down(cpu, 0, target);
    }
    
    static int cpu_down(unsigned int cpu, enum cpuhp_state target)
    {
    	int err;
    
    	cpu_maps_update_begin();
    	err = cpu_down_maps_locked(cpu, target);
    	cpu_maps_update_done();
    	return err;
    }
    
    /**
     * cpu_device_down - Bring down a cpu device
     * @dev: Pointer to the cpu device to offline
     *
     * This function is meant to be used by device core cpu subsystem only.
     *
     * Other subsystems should use remove_cpu() instead.
     */
    int cpu_device_down(struct device *dev)
    {
    	return cpu_down(dev->id, CPUHP_OFFLINE);
    }
    
    int remove_cpu(unsigned int cpu)
    {
    	int ret;
    
    	lock_device_hotplug();
    	ret = device_offline(get_cpu_device(cpu));
    	unlock_device_hotplug();
    
    	return ret;
    }
    EXPORT_SYMBOL_GPL(remove_cpu);
    
    void smp_shutdown_nonboot_cpus(unsigned int primary_cpu)
    {
    	unsigned int cpu;
    	int error;
    
    	cpu_maps_update_begin();
    
    	/*
    	 * Make certain the cpu I'm about to reboot on is online.
    	 *
    	 * This is inline to what migrate_to_reboot_cpu() already do.
    	 */
    	if (!cpu_online(primary_cpu))
    		primary_cpu = cpumask_first(cpu_online_mask);
    
    	for_each_online_cpu(cpu) {
    		if (cpu == primary_cpu)
    			continue;
    
    		error = cpu_down_maps_locked(cpu, CPUHP_OFFLINE);
    		if (error) {
    			pr_err("Failed to offline CPU%d - error=%d",
    				cpu, error);
    			break;
    		}
    	}
    
    	/*
    	 * Ensure all but the reboot CPU are offline.
    	 */
    	BUG_ON(num_online_cpus() > 1);
    
    	/*
    	 * Make sure the CPUs won't be enabled by someone else after this
    	 * point. Kexec will reboot to a new kernel shortly resetting
    	 * everything along the way.
    	 */
    	cpu_hotplug_disabled++;
    
    	cpu_maps_update_done();
    }
    
    #else
    #define takedown_cpu		NULL
    #endif /*CONFIG_HOTPLUG_CPU*/
    
    /**
     * notify_cpu_starting(cpu) - Invoke the callbacks on the starting CPU
     * @cpu: cpu that just started
     *
     * It must be called by the arch code on the new cpu, before the new cpu
     * enables interrupts and before the "boot" cpu returns from __cpu_up().
     */
    void notify_cpu_starting(unsigned int cpu)
    {
    	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
    	enum cpuhp_state target = min((int)st->target, CPUHP_AP_ONLINE);
    	int ret;
    
    	rcu_cpu_starting(cpu);	/* Enables RCU usage on this CPU. */
    	cpumask_set_cpu(cpu, &cpus_booted_once_mask);
    	while (st->state < target) {
    		st->state++;
    		ret = cpuhp_invoke_callback(cpu, st->state, true, NULL, NULL);
    		/*
    		 * STARTING must not fail!
    		 */
    		WARN_ON_ONCE(ret);
    	}
    }
    
    /*
     * Called from the idle task. Wake up the controlling task which brings the
     * hotplug thread of the upcoming CPU up and then delegates the rest of the
     * online bringup to the hotplug thread.
     */
    void cpuhp_online_idle(enum cpuhp_state state)
    {
    	struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
    
    	/* Happens for the boot cpu */
    	if (state != CPUHP_AP_ONLINE_IDLE)
    		return;
    
    	/*
    	 * Unpart the stopper thread before we start the idle loop (and start
    	 * scheduling); this ensures the stopper task is always available.
    	 */
    	stop_machine_unpark(smp_processor_id());
    
    	st->state = CPUHP_AP_ONLINE_IDLE;
    	complete_ap_thread(st, true);
    }
    
    /* Requires cpu_add_remove_lock to be held */
    static int _cpu_up(unsigned int cpu, int tasks_frozen, enum cpuhp_state target)
    {
    	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
    	struct task_struct *idle;
    	int ret = 0;
    
    	cpus_write_lock();
    
    	if (!cpu_present(cpu)) {
    		ret = -EINVAL;
    		goto out;
    	}
    
    	/*
    	 * The caller of cpu_up() might have raced with another
    	 * caller. Nothing to do.
    	 */
    	if (st->state >= target)
    		goto out;
    
    	if (st->state == CPUHP_OFFLINE) {
    		/* Let it fail before we try to bring the cpu up */
    		idle = idle_thread_get(cpu);
    		if (IS_ERR(idle)) {
    			ret = PTR_ERR(idle);
    			goto out;
    		}
    	}
    
    	cpuhp_tasks_frozen = tasks_frozen;
    
    	cpuhp_set_state(st, target);
    	/*
    	 * If the current CPU state is in the range of the AP hotplug thread,
    	 * then we need to kick the thread once more.
    	 */
    	if (st->state > CPUHP_BRINGUP_CPU) {
    		ret = cpuhp_kick_ap_work(cpu);
    		/*
    		 * The AP side has done the error rollback already. Just
    		 * return the error code..
    		 */
    		if (ret)
    			goto out;
    	}
    
    	/*
    	 * Try to reach the target state. We max out on the BP at
    	 * CPUHP_BRINGUP_CPU. After that the AP hotplug thread is
    	 * responsible for bringing it up to the target state.
    	 */
    	target = min((int)target, CPUHP_BRINGUP_CPU);
    	ret = cpuhp_up_callbacks(cpu, st, target);
    out:
    	cpus_write_unlock();
    	arch_smt_update();
    	return ret;
    }
    
    static int cpu_up(unsigned int cpu, enum cpuhp_state target)
    {
    	int err = 0;
    
    	if (!cpu_possible(cpu)) {
    		pr_err("can't online cpu %d because it is not configured as may-hotadd at boot time\n",
    		       cpu);
    #if defined(CONFIG_IA64)
    		pr_err("please check additional_cpus= boot parameter\n");
    #endif
    		return -EINVAL;
    	}
    
    	err = try_online_node(cpu_to_node(cpu));
    	if (err)
    		return err;
    
    	cpu_maps_update_begin();
    
    	if (cpu_hotplug_disabled) {
    		err = -EBUSY;
    		goto out;
    	}
    	if (!cpu_smt_allowed(cpu)) {
    		err = -EPERM;
    		goto out;
    	}
    
    	err = _cpu_up(cpu, 0, target);
    out:
    	cpu_maps_update_done();
    	return err;
    }
    
    /**
     * cpu_device_up - Bring up a cpu device
     * @dev: Pointer to the cpu device to online
     *
     * This function is meant to be used by device core cpu subsystem only.
     *
     * Other subsystems should use add_cpu() instead.
     */
    int cpu_device_up(struct device *dev)
    {
    	return cpu_up(dev->id, CPUHP_ONLINE);
    }
    
    int add_cpu(unsigned int cpu)
    {
    	int ret;
    
    	lock_device_hotplug();
    	ret = device_online(get_cpu_device(cpu));
    	unlock_device_hotplug();
    
    	return ret;
    }
    EXPORT_SYMBOL_GPL(add_cpu);
    
    /**
     * bringup_hibernate_cpu - Bring up the CPU that we hibernated on
     * @sleep_cpu: The cpu we hibernated on and should be brought up.
     *
     * On some architectures like arm64, we can hibernate on any CPU, but on
     * wake up the CPU we hibernated on might be offline as a side effect of
     * using maxcpus= for example.
     */
    int bringup_hibernate_cpu(unsigned int sleep_cpu)
    {
    	int ret;
    
    	if (!cpu_online(sleep_cpu)) {
    		pr_info("Hibernated on a CPU that is offline! Bringing CPU up.\n");
    		ret = cpu_up(sleep_cpu, CPUHP_ONLINE);
    		if (ret) {
    			pr_err("Failed to bring hibernate-CPU up!\n");
    			return ret;
    		}
    	}
    	return 0;
    }
    
    void bringup_nonboot_cpus(unsigned int setup_max_cpus)
    {
    	unsigned int cpu;
    
    	for_each_present_cpu(cpu) {
    		if (num_online_cpus() >= setup_max_cpus)
    			break;
    		if (!cpu_online(cpu))
    			cpu_up(cpu, CPUHP_ONLINE);
    	}
    }
    
    #ifdef CONFIG_PM_SLEEP_SMP
    static cpumask_var_t frozen_cpus;
    
    int __freeze_secondary_cpus(int primary, bool suspend)
    {
    	int cpu, error = 0;
    
    	cpu_maps_update_begin();
    	if (primary == -1) {
    		primary = cpumask_first(cpu_online_mask);
    		if (!housekeeping_cpu(primary, HK_FLAG_TIMER))
    			primary = housekeeping_any_cpu(HK_FLAG_TIMER);
    	} else {
    		if (!cpu_online(primary))
    			primary = cpumask_first(cpu_online_mask);
    	}
    
    	/*
    	 * We take down all of the non-boot CPUs in one shot to avoid races
    	 * with the userspace trying to use the CPU hotplug at the same time
    	 */
    	cpumask_clear(frozen_cpus);
    
    	pr_info("Disabling non-boot CPUs ...\n");
    	for_each_online_cpu(cpu) {
    		if (cpu == primary)
    			continue;
    
    		if (suspend && pm_wakeup_pending()) {
    			pr_info("Wakeup pending. Abort CPU freeze\n");
    			error = -EBUSY;
    			break;
    		}
    
    		trace_suspend_resume(TPS("CPU_OFF"), cpu, true);
    		error = _cpu_down(cpu, 1, CPUHP_OFFLINE);
    		trace_suspend_resume(TPS("CPU_OFF"), cpu, false);
    		if (!error)
    			cpumask_set_cpu(cpu, frozen_cpus);
    		else {
    			pr_err("Error taking CPU%d down: %d\n", cpu, error);
    			break;
    		}
    	}
    
    	if (!error)
    		BUG_ON(num_online_cpus() > 1);
    	else
    		pr_err("Non-boot CPUs are not disabled\n");
    
    	/*
    	 * Make sure the CPUs won't be enabled by someone else. We need to do
    	 * this even in case of failure as all disable_nonboot_cpus() users are
    	 * supposed to do enable_nonboot_cpus() on the failure path.
    	 */
    	cpu_hotplug_disabled++;
    
    	cpu_maps_update_done();
    	return error;
    }
    
    void __weak arch_enable_nonboot_cpus_begin(void)
    {
    }
    
    void __weak arch_enable_nonboot_cpus_end(void)
    {
    }
    
    void enable_nonboot_cpus(void)
    {
    	int cpu, error;
    
    	/* Allow everyone to use the CPU hotplug again */
    	cpu_maps_update_begin();
    	__cpu_hotplug_enable();
    	if (cpumask_empty(frozen_cpus))
    		goto out;
    
    	pr_info("Enabling non-boot CPUs ...\n");
    
    	arch_enable_nonboot_cpus_begin();
    
    	for_each_cpu(cpu, frozen_cpus) {
    		trace_suspend_resume(TPS("CPU_ON"), cpu, true);
    		error = _cpu_up(cpu, 1, CPUHP_ONLINE);
    		trace_suspend_resume(TPS("CPU_ON"), cpu, false);
    		if (!error) {
    			pr_info("CPU%d is up\n", cpu);
    			continue;
    		}
    		pr_warn("Error taking CPU%d up: %d\n", cpu, error);
    	}
    
    	arch_enable_nonboot_cpus_end();
    
    	cpumask_clear(frozen_cpus);
    out:
    	cpu_maps_update_done();
    }
    
    static int __init alloc_frozen_cpus(void)
    {
    	if (!alloc_cpumask_var(&frozen_cpus, GFP_KERNEL|__GFP_ZERO))
    		return -ENOMEM;
    	return 0;
    }
    core_initcall(alloc_frozen_cpus);
    
    /*
     * When callbacks for CPU hotplug notifications are being executed, we must
     * ensure that the state of the system with respect to the tasks being frozen
     * or not, as reported by the notification, remains unchanged *throughout the
     * duration* of the execution of the callbacks.
     * Hence we need to prevent the freezer from racing with regular CPU hotplug.
     *
     * This synchronization is implemented by mutually excluding regular CPU
     * hotplug and Suspend/Hibernate call paths by hooking onto the Suspend/
     * Hibernate notifications.
     */
    static int
    cpu_hotplug_pm_callback(struct notifier_block *nb,
    			unsigned long action, void *ptr)
    {
    	switch (action) {
    
    	case PM_SUSPEND_PREPARE:
    	case PM_HIBERNATION_PREPARE:
    		cpu_hotplug_disable();
    		break;
    
    	case PM_POST_SUSPEND:
    	case PM_POST_HIBERNATION:
    		cpu_hotplug_enable();
    		break;
    
    	default:
    		return NOTIFY_DONE;
    	}
    
    	return NOTIFY_OK;
    }
    
    
    static int __init cpu_hotplug_pm_sync_init(void)
    {
    	/*
    	 * cpu_hotplug_pm_callback has higher priority than x86
    	 * bsp_pm_callback which depends on cpu_hotplug_pm_callback
    	 * to disable cpu hotplug to avoid cpu hotplug race.
    	 */
    	pm_notifier(cpu_hotplug_pm_callback, 0);
    	return 0;
    }
    core_initcall(cpu_hotplug_pm_sync_init);
    
    #endif /* CONFIG_PM_SLEEP_SMP */
    
    int __boot_cpu_id;
    
    #endif /* CONFIG_SMP */
    
    /* Boot processor state steps */
    static struct cpuhp_step cpuhp_hp_states[] = {
    	[CPUHP_OFFLINE] = {
    		.name			= "offline",
    		.startup.single		= NULL,
    		.teardown.single	= NULL,
    	},
    #ifdef CONFIG_SMP
    	[CPUHP_CREATE_THREADS]= {
    		.name			= "threads:prepare",
    		.startup.single		= smpboot_create_threads,
    		.teardown.single	= NULL,
    		.cant_stop		= true,
    	},
    	[CPUHP_PERF_PREPARE] = {
    		.name			= "perf:prepare",
    		.startup.single		= perf_event_init_cpu,
    		.teardown.single	= perf_event_exit_cpu,
    	},
    	[CPUHP_WORKQUEUE_PREP] = {
    		.name			= "workqueue:prepare",
    		.startup.single		= workqueue_prepare_cpu,
    		.teardown.single	= NULL,
    	},
    	[CPUHP_HRTIMERS_PREPARE] = {
    		.name			= "hrtimers:prepare",
    		.startup.single		= hrtimers_prepare_cpu,
    		.teardown.single	= hrtimers_dead_cpu,
    	},
    	[CPUHP_SMPCFD_PREPARE] = {
    		.name			= "smpcfd:prepare",
    		.startup.single		= smpcfd_prepare_cpu,
    		.teardown.single	= smpcfd_dead_cpu,
    	},
    	[CPUHP_RELAY_PREPARE] = {
    		.name			= "relay:prepare",
    		.startup.single		= relay_prepare_cpu,
    		.teardown.single	= NULL,
    	},
    	[CPUHP_SLAB_PREPARE] = {
    		.name			= "slab:prepare",
    		.startup.single		= slab_prepare_cpu,
    		.teardown.single	= slab_dead_cpu,
    	},
    	[CPUHP_RCUTREE_PREP] = {
    		.name			= "RCU/tree:prepare",
    		.startup.single		= rcutree_prepare_cpu,
    		.teardown.single	= rcutree_dead_cpu,
    	},
    	/*
    	 * On the tear-down path, timers_dead_cpu() must be invoked
    	 * before blk_mq_queue_reinit_notify() from notify_dead(),
    	 * otherwise a RCU stall occurs.
    	 */
    	[CPUHP_TIMERS_PREPARE] = {
    		.name			= "timers:prepare",
    		.startup.single		= timers_prepare_cpu,
    		.teardown.single	= timers_dead_cpu,
    	},
    	/* Kicks the plugged cpu into life */
    	[CPUHP_BRINGUP_CPU] = {
    		.name			= "cpu:bringup",
    		.startup.single		= bringup_cpu,
    		.teardown.single	= NULL,
    		.cant_stop		= true,
    	},
    	/* Final state before CPU kills itself */
    	[CPUHP_AP_IDLE_DEAD] = {
    		.name			= "idle:dead",
    	},
    	/*
    	 * Last state before CPU enters the idle loop to die. Transient state
    	 * for synchronization.
    	 */
    	[CPUHP_AP_OFFLINE] = {
    		.name			= "ap:offline",
    		.cant_stop		= true,
    	},
    	/* First state is scheduler control. Interrupts are disabled */
    	[CPUHP_AP_SCHED_STARTING] = {
    		.name			= "sched:starting",
    		.startup.single		= sched_cpu_starting,
    		.teardown.single	= sched_cpu_dying,
    	},
    	[CPUHP_AP_RCUTREE_DYING] = {
    		.name			= "RCU/tree:dying",
    		.startup.single		= NULL,
    		.teardown.single	= rcutree_dying_cpu,
    	},
    	[CPUHP_AP_SMPCFD_DYING] = {
    		.name			= "smpcfd:dying",
    		.startup.single		= NULL,
    		.teardown.single	= smpcfd_dying_cpu,
    	},
    	/* Entry state on starting. Interrupts enabled from here on. Transient
    	 * state for synchronsization */
    	[CPUHP_AP_ONLINE] = {
    		.name			= "ap:online",
    	},
    	/*
    	 * Handled on controll processor until the plugged processor manages
    	 * this itself.
    	 */
    	[CPUHP_TEARDOWN_CPU] = {
    		.name			= "cpu:teardown",
    		.startup.single		= NULL,
    		.teardown.single	= takedown_cpu,
    		.cant_stop		= true,
    	},
    	/* Handle smpboot threads park/unpark */
    	[CPUHP_AP_SMPBOOT_THREADS] = {
    		.name			= "smpboot/threads:online",
    		.startup.single		= smpboot_unpark_threads,
    		.teardown.single	= smpboot_park_threads,
    	},
    	[CPUHP_AP_IRQ_AFFINITY_ONLINE] = {
    		.name			= "irq/affinity:online",
    		.startup.single		= irq_affinity_online_cpu,
    		.teardown.single	= NULL,
    	},
    	[CPUHP_AP_PERF_ONLINE] = {
    		.name			= "perf:online",
    		.startup.single		= perf_event_init_cpu,
    		.teardown.single	= perf_event_exit_cpu,
    	},
    	[CPUHP_AP_WATCHDOG_ONLINE] = {
    		.name			= "lockup_detector:online",
    		.startup.single		= lockup_detector_online_cpu,
    		.teardown.single	= lockup_detector_offline_cpu,
    	},
    	[CPUHP_AP_WORKQUEUE_ONLINE] = {
    		.name			= "workqueue:online",
    		.startup.single		= workqueue_online_cpu,
    		.teardown.single	= workqueue_offline_cpu,
    	},
    	[CPUHP_AP_RCUTREE_ONLINE] = {
    		.name			= "RCU/tree:online",
    		.startup.single		= rcutree_online_cpu,
    		.teardown.single	= rcutree_offline_cpu,
    	},
    #endif
    	/*
    	 * The dynamically registered state space is here
    	 */
    
    #ifdef CONFIG_SMP
    	/* Last state is scheduler control setting the cpu active */
    	[CPUHP_AP_ACTIVE] = {
    		.name			= "sched:active",
    		.startup.single		= sched_cpu_activate,
    		.teardown.single	= sched_cpu_deactivate,
    	},
    #endif
    
    	/* CPU is fully up and running. */
    	[CPUHP_ONLINE] = {
    		.name			= "online",
    		.startup.single		= NULL,
    		.teardown.single	= NULL,
    	},
    };
    
    /* Sanity check for callbacks */
    static int cpuhp_cb_check(enum cpuhp_state state)
    {
    	if (state <= CPUHP_OFFLINE || state >= CPUHP_ONLINE)
    		return -EINVAL;
    	return 0;
    }
    
    /*
     * Returns a free for dynamic slot assignment of the Online state. The states
     * are protected by the cpuhp_slot_states mutex and an empty slot is identified
     * by having no name assigned.
     */
    static int cpuhp_reserve_state(enum cpuhp_state state)
    {
    	enum cpuhp_state i, end;
    	struct cpuhp_step *step;
    
    	switch (state) {
    	case CPUHP_AP_ONLINE_DYN:
    		step = cpuhp_hp_states + CPUHP_AP_ONLINE_DYN;
    		end = CPUHP_AP_ONLINE_DYN_END;
    		break;
    	case CPUHP_BP_PREPARE_DYN:
    		step = cpuhp_hp_states + CPUHP_BP_PREPARE_DYN;
    		end = CPUHP_BP_PREPARE_DYN_END;
    		break;
    	default:
    		return -EINVAL;
    	}
    
    	for (i = state; i <= end; i++, step++) {
    		if (!step->name)
    			return i;
    	}
    	WARN(1, "No more dynamic states available for CPU hotplug\n");
    	return -ENOSPC;
    }
    
    static int cpuhp_store_callbacks(enum cpuhp_state state, const char *name,
    				 int (*startup)(unsigned int cpu),
    				 int (*teardown)(unsigned int cpu),
    				 bool multi_instance)
    {
    	/* (Un)Install the callbacks for further cpu hotplug operations */
    	struct cpuhp_step *sp;
    	int ret = 0;
    
    	/*
    	 * If name is NULL, then the state gets removed.
    	 *
    	 * CPUHP_AP_ONLINE_DYN and CPUHP_BP_PREPARE_DYN are handed out on
    	 * the first allocation from these dynamic ranges, so the removal
    	 * would trigger a new allocation and clear the wrong (already
    	 * empty) state, leaving the callbacks of the to be cleared state
    	 * dangling, which causes wreckage on the next hotplug operation.
    	 */
    	if (name && (state == CPUHP_AP_ONLINE_DYN ||
    		     state == CPUHP_BP_PREPARE_DYN)) {
    		ret = cpuhp_reserve_state(state);
    		if (ret < 0)
    			return ret;
    		state = ret;
    	}
    	sp = cpuhp_get_step(state);
    	if (name && sp->name)
    		return -EBUSY;
    
    	sp->startup.single = startup;
    	sp->teardown.single = teardown;
    	sp->name = name;
    	sp->multi_instance = multi_instance;
    	INIT_HLIST_HEAD(&sp->list);
    	return ret;
    }
    
    static void *cpuhp_get_teardown_cb(enum cpuhp_state state)
    {
    	return cpuhp_get_step(state)->teardown.single;
    }
    
    /*
     * Call the startup/teardown function for a step either on the AP or
     * on the current CPU.
     */
    static int cpuhp_issue_call(int cpu, enum cpuhp_state state, bool bringup,
    			    struct hlist_node *node)
    {
    	struct cpuhp_step *sp = cpuhp_get_step(state);
    	int ret;
    
    	/*
    	 * If there's nothing to do, we done.
    	 * Relies on the union for multi_instance.
    	 */
    	if ((bringup && !sp->startup.single) ||
    	    (!bringup && !sp->teardown.single))
    		return 0;
    	/*
    	 * The non AP bound callbacks can fail on bringup. On teardown
    	 * e.g. module removal we crash for now.
    	 */
    #ifdef CONFIG_SMP
    	if (cpuhp_is_ap_state(state))
    		ret = cpuhp_invoke_ap_callback(cpu, state, bringup, node);
    	else
    		ret = cpuhp_invoke_callback(cpu, state, bringup, node, NULL);
    #else
    	ret = cpuhp_invoke_callback(cpu, state, bringup, node, NULL);
    #endif
    	BUG_ON(ret && !bringup);
    	return ret;
    }
    
    /*
     * Called from __cpuhp_setup_state on a recoverable failure.
     *
     * Note: The teardown callbacks for rollback are not allowed to fail!
     */
    static void cpuhp_rollback_install(int failedcpu, enum cpuhp_state state,
    				   struct hlist_node *node)
    {
    	int cpu;
    
    	/* Roll back the already executed steps on the other cpus */
    	for_each_present_cpu(cpu) {
    		struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
    		int cpustate = st->state;
    
    		if (cpu >= failedcpu)
    			break;
    
    		/* Did we invoke the startup call on that cpu ? */
    		if (cpustate >= state)
    			cpuhp_issue_call(cpu, state, false, node);
    	}
    }
    
    int __cpuhp_state_add_instance_cpuslocked(enum cpuhp_state state,
    					  struct hlist_node *node,
    					  bool invoke)
    {
    	struct cpuhp_step *sp;
    	int cpu;
    	int ret;
    
    	lockdep_assert_cpus_held();
    
    	sp = cpuhp_get_step(state);
    	if (sp->multi_instance == false)
    		return -EINVAL;
    
    	mutex_lock(&cpuhp_state_mutex);
    
    	if (!invoke || !sp->startup.multi)
    		goto add_node;
    
    	/*
    	 * Try to call the startup callback for each present cpu
    	 * depending on the hotplug state of the cpu.
    	 */
    	for_each_present_cpu(cpu) {
    		struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
    		int cpustate = st->state;
    
    		if (cpustate < state)
    			continue;
    
    		ret = cpuhp_issue_call(cpu, state, true, node);
    		if (ret) {
    			if (sp->teardown.multi)
    				cpuhp_rollback_install(cpu, state, node);
    			goto unlock;
    		}
    	}
    add_node:
    	ret = 0;
    	hlist_add_head(node, &sp->list);
    unlock:
    	mutex_unlock(&cpuhp_state_mutex);
    	return ret;
    }
    
    int __cpuhp_state_add_instance(enum cpuhp_state state, struct hlist_node *node,
    			       bool invoke)
    {
    	int ret;
    
    	cpus_read_lock();
    	ret = __cpuhp_state_add_instance_cpuslocked(state, node, invoke);
    	cpus_read_unlock();
    	return ret;
    }
    EXPORT_SYMBOL_GPL(__cpuhp_state_add_instance);
    
    /**
     * __cpuhp_setup_state_cpuslocked - Setup the callbacks for an hotplug machine state
     * @state:		The state to setup
     * @invoke:		If true, the startup function is invoked for cpus where
     *			cpu state >= @state
     * @startup:		startup callback function
     * @teardown:		teardown callback function
     * @multi_instance:	State is set up for multiple instances which get
     *			added afterwards.
     *
     * The caller needs to hold cpus read locked while calling this function.
     * Returns:
     *   On success:
     *      Positive state number if @state is CPUHP_AP_ONLINE_DYN
     *      0 for all other states
     *   On failure: proper (negative) error code
     */
    int __cpuhp_setup_state_cpuslocked(enum cpuhp_state state,
    				   const char *name, bool invoke,
    				   int (*startup)(unsigned int cpu),
    				   int (*teardown)(unsigned int cpu),
    				   bool multi_instance)
    {
    	int cpu, ret = 0;
    	bool dynstate;
    
    	lockdep_assert_cpus_held();
    
    	if (cpuhp_cb_check(state) || !name)
    		return -EINVAL;
    
    	mutex_lock(&cpuhp_state_mutex);
    
    	ret = cpuhp_store_callbacks(state, name, startup, teardown,
    				    multi_instance);
    
    	dynstate = state == CPUHP_AP_ONLINE_DYN;
    	if (ret > 0 && dynstate) {
    		state = ret;
    		ret = 0;
    	}
    
    	if (ret || !invoke || !startup)
    		goto out;
    
    	/*
    	 * Try to call the startup callback for each present cpu
    	 * depending on the hotplug state of the cpu.
    	 */
    	for_each_present_cpu(cpu) {
    		struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
    		int cpustate = st->state;
    
    		if (cpustate < state)
    			continue;
    
    		ret = cpuhp_issue_call(cpu, state, true, NULL);
    		if (ret) {
    			if (teardown)
    				cpuhp_rollback_install(cpu, state, NULL);
    			cpuhp_store_callbacks(state, NULL, NULL, NULL, false);
    			goto out;
    		}
    	}
    out:
    	mutex_unlock(&cpuhp_state_mutex);
    	/*
    	 * If the requested state is CPUHP_AP_ONLINE_DYN, return the
    	 * dynamically allocated state in case of success.
    	 */
    	if (!ret && dynstate)
    		return state;
    	return ret;
    }
    EXPORT_SYMBOL(__cpuhp_setup_state_cpuslocked);
    
    int __cpuhp_setup_state(enum cpuhp_state state,
    			const char *name, bool invoke,
    			int (*startup)(unsigned int cpu),
    			int (*teardown)(unsigned int cpu),
    			bool multi_instance)
    {
    	int ret;
    
    	cpus_read_lock();
    	ret = __cpuhp_setup_state_cpuslocked(state, name, invoke, startup,
    					     teardown, multi_instance);
    	cpus_read_unlock();
    	return ret;
    }
    EXPORT_SYMBOL(__cpuhp_setup_state);
    
    int __cpuhp_state_remove_instance(enum cpuhp_state state,
    				  struct hlist_node *node, bool invoke)
    {
    	struct cpuhp_step *sp = cpuhp_get_step(state);
    	int cpu;
    
    	BUG_ON(cpuhp_cb_check(state));
    
    	if (!sp->multi_instance)
    		return -EINVAL;
    
    	cpus_read_lock();
    	mutex_lock(&cpuhp_state_mutex);
    
    	if (!invoke || !cpuhp_get_teardown_cb(state))
    		goto remove;
    	/*
    	 * Call the teardown callback for each present cpu depending
    	 * on the hotplug state of the cpu. This function is not
    	 * allowed to fail currently!
    	 */
    	for_each_present_cpu(cpu) {
    		struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
    		int cpustate = st->state;
    
    		if (cpustate >= state)
    			cpuhp_issue_call(cpu, state, false, node);
    	}
    
    remove:
    	hlist_del(node);
    	mutex_unlock(&cpuhp_state_mutex);
    	cpus_read_unlock();
    
    	return 0;
    }
    EXPORT_SYMBOL_GPL(__cpuhp_state_remove_instance);
    
    /**
     * __cpuhp_remove_state_cpuslocked - Remove the callbacks for an hotplug machine state
     * @state:	The state to remove
     * @invoke:	If true, the teardown function is invoked for cpus where
     *		cpu state >= @state
     *
     * The caller needs to hold cpus read locked while calling this function.
     * The teardown callback is currently not allowed to fail. Think
     * about module removal!
     */
    void __cpuhp_remove_state_cpuslocked(enum cpuhp_state state, bool invoke)
    {
    	struct cpuhp_step *sp = cpuhp_get_step(state);
    	int cpu;
    
    	BUG_ON(cpuhp_cb_check(state));
    
    	lockdep_assert_cpus_held();
    
    	mutex_lock(&cpuhp_state_mutex);
    	if (sp->multi_instance) {
    		WARN(!hlist_empty(&sp->list),
    		     "Error: Removing state %d which has instances left.\n",
    		     state);
    		goto remove;
    	}
    
    	if (!invoke || !cpuhp_get_teardown_cb(state))
    		goto remove;
    
    	/*
    	 * Call the teardown callback for each present cpu depending
    	 * on the hotplug state of the cpu. This function is not
    	 * allowed to fail currently!
    	 */
    	for_each_present_cpu(cpu) {
    		struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
    		int cpustate = st->state;
    
    		if (cpustate >= state)
    			cpuhp_issue_call(cpu, state, false, NULL);
    	}
    remove:
    	cpuhp_store_callbacks(state, NULL, NULL, NULL, false);
    	mutex_unlock(&cpuhp_state_mutex);
    }
    EXPORT_SYMBOL(__cpuhp_remove_state_cpuslocked);
    
    void __cpuhp_remove_state(enum cpuhp_state state, bool invoke)
    {
    	cpus_read_lock();
    	__cpuhp_remove_state_cpuslocked(state, invoke);
    	cpus_read_unlock();
    }
    EXPORT_SYMBOL(__cpuhp_remove_state);
    
    #ifdef CONFIG_HOTPLUG_SMT
    static void cpuhp_offline_cpu_device(unsigned int cpu)
    {
    	struct device *dev = get_cpu_device(cpu);
    
    	dev->offline = true;
    	/* Tell user space about the state change */
    	kobject_uevent(&dev->kobj, KOBJ_OFFLINE);
    }
    
    static void cpuhp_online_cpu_device(unsigned int cpu)
    {
    	struct device *dev = get_cpu_device(cpu);
    
    	dev->offline = false;
    	/* Tell user space about the state change */
    	kobject_uevent(&dev->kobj, KOBJ_ONLINE);
    }
    
    int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval)
    {
    	int cpu, ret = 0;
    
    	cpu_maps_update_begin();
    	for_each_online_cpu(cpu) {
    		if (topology_is_primary_thread(cpu))
    			continue;
    		ret = cpu_down_maps_locked(cpu, CPUHP_OFFLINE);
    		if (ret)
    			break;
    		/*
    		 * As this needs to hold the cpu maps lock it's impossible
    		 * to call device_offline() because that ends up calling
    		 * cpu_down() which takes cpu maps lock. cpu maps lock
    		 * needs to be held as this might race against in kernel
    		 * abusers of the hotplug machinery (thermal management).
    		 *
    		 * So nothing would update device:offline state. That would
    		 * leave the sysfs entry stale and prevent onlining after
    		 * smt control has been changed to 'off' again. This is
    		 * called under the sysfs hotplug lock, so it is properly
    		 * serialized against the regular offline usage.
    		 */
    		cpuhp_offline_cpu_device(cpu);
    	}
    	if (!ret)
    		cpu_smt_control = ctrlval;
    	cpu_maps_update_done();
    	return ret;
    }
    
    int cpuhp_smt_enable(void)
    {
    	int cpu, ret = 0;
    
    	cpu_maps_update_begin();
    	cpu_smt_control = CPU_SMT_ENABLED;
    	for_each_present_cpu(cpu) {
    		/* Skip online CPUs and CPUs on offline nodes */
    		if (cpu_online(cpu) || !node_online(cpu_to_node(cpu)))
    			continue;
    		ret = _cpu_up(cpu, 0, CPUHP_ONLINE);
    		if (ret)
    			break;
    		/* See comment in cpuhp_smt_disable() */
    		cpuhp_online_cpu_device(cpu);
    	}
    	cpu_maps_update_done();
    	return ret;
    }
    #endif
    
    #if defined(CONFIG_SYSFS) && defined(CONFIG_HOTPLUG_CPU)
    static ssize_t show_cpuhp_state(struct device *dev,
    				struct device_attribute *attr, char *buf)
    {
    	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);
    
    	return sprintf(buf, "%d\n", st->state);
    }
    static DEVICE_ATTR(state, 0444, show_cpuhp_state, NULL);
    
    static ssize_t write_cpuhp_target(struct device *dev,
    				  struct device_attribute *attr,
    				  const char *buf, size_t count)
    {
    	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);
    	struct cpuhp_step *sp;
    	int target, ret;
    
    	ret = kstrtoint(buf, 10, &target);
    	if (ret)
    		return ret;
    
    #ifdef CONFIG_CPU_HOTPLUG_STATE_CONTROL
    	if (target < CPUHP_OFFLINE || target > CPUHP_ONLINE)
    		return -EINVAL;
    #else
    	if (target != CPUHP_OFFLINE && target != CPUHP_ONLINE)
    		return -EINVAL;
    #endif
    
    	ret = lock_device_hotplug_sysfs();
    	if (ret)
    		return ret;
    
    	mutex_lock(&cpuhp_state_mutex);
    	sp = cpuhp_get_step(target);
    	ret = !sp->name || sp->cant_stop ? -EINVAL : 0;
    	mutex_unlock(&cpuhp_state_mutex);
    	if (ret)
    		goto out;
    
    	if (st->state < target)
    		ret = cpu_up(dev->id, target);
    	else
    		ret = cpu_down(dev->id, target);
    out:
    	unlock_device_hotplug();
    	return ret ? ret : count;
    }
    
    static ssize_t show_cpuhp_target(struct device *dev,
    				 struct device_attribute *attr, char *buf)
    {
    	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);
    
    	return sprintf(buf, "%d\n", st->target);
    }
    static DEVICE_ATTR(target, 0644, show_cpuhp_target, write_cpuhp_target);
    
    
    static ssize_t write_cpuhp_fail(struct device *dev,
    				struct device_attribute *attr,
    				const char *buf, size_t count)
    {
    	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);
    	struct cpuhp_step *sp;
    	int fail, ret;
    
    	ret = kstrtoint(buf, 10, &fail);
    	if (ret)
    		return ret;
    
    	if (fail < CPUHP_OFFLINE || fail > CPUHP_ONLINE)
    		return -EINVAL;
    
    	/*
    	 * Cannot fail STARTING/DYING callbacks.
    	 */
    	if (cpuhp_is_atomic_state(fail))
    		return -EINVAL;
    
    	/*
    	 * Cannot fail anything that doesn't have callbacks.
    	 */
    	mutex_lock(&cpuhp_state_mutex);
    	sp = cpuhp_get_step(fail);
    	if (!sp->startup.single && !sp->teardown.single)
    		ret = -EINVAL;
    	mutex_unlock(&cpuhp_state_mutex);
    	if (ret)
    		return ret;
    
    	st->fail = fail;
    
    	return count;
    }
    
    static ssize_t show_cpuhp_fail(struct device *dev,
    			       struct device_attribute *attr, char *buf)
    {
    	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);
    
    	return sprintf(buf, "%d\n", st->fail);
    }
    
    static DEVICE_ATTR(fail, 0644, show_cpuhp_fail, write_cpuhp_fail);
    
    static struct attribute *cpuhp_cpu_attrs[] = {
    	&dev_attr_state.attr,
    	&dev_attr_target.attr,
    	&dev_attr_fail.attr,
    	NULL
    };
    
    static const struct attribute_group cpuhp_cpu_attr_group = {
    	.attrs = cpuhp_cpu_attrs,
    	.name = "hotplug",
    	NULL
    };
    
    static ssize_t show_cpuhp_states(struct device *dev,
    				 struct device_attribute *attr, char *buf)
    {
    	ssize_t cur, res = 0;
    	int i;
    
    	mutex_lock(&cpuhp_state_mutex);
    	for (i = CPUHP_OFFLINE; i <= CPUHP_ONLINE; i++) {
    		struct cpuhp_step *sp = cpuhp_get_step(i);
    
    		if (sp->name) {
    			cur = sprintf(buf, "%3d: %s\n", i, sp->name);
    			buf += cur;
    			res += cur;
    		}
    	}
    	mutex_unlock(&cpuhp_state_mutex);
    	return res;
    }
    static DEVICE_ATTR(states, 0444, show_cpuhp_states, NULL);
    
    static struct attribute *cpuhp_cpu_root_attrs[] = {
    	&dev_attr_states.attr,
    	NULL
    };
    
    static const struct attribute_group cpuhp_cpu_root_attr_group = {
    	.attrs = cpuhp_cpu_root_attrs,
    	.name = "hotplug",
    	NULL
    };
    
    #ifdef CONFIG_HOTPLUG_SMT
    
    static ssize_t
    __store_smt_control(struct device *dev, struct device_attribute *attr,
    		    const char *buf, size_t count)
    {
    	int ctrlval, ret;
    
    	if (sysfs_streq(buf, "on"))
    		ctrlval = CPU_SMT_ENABLED;
    	else if (sysfs_streq(buf, "off"))
    		ctrlval = CPU_SMT_DISABLED;
    	else if (sysfs_streq(buf, "forceoff"))
    		ctrlval = CPU_SMT_FORCE_DISABLED;
    	else
    		return -EINVAL;
    
    	if (cpu_smt_control == CPU_SMT_FORCE_DISABLED)
    		return -EPERM;
    
    	if (cpu_smt_control == CPU_SMT_NOT_SUPPORTED)
    		return -ENODEV;
    
    	ret = lock_device_hotplug_sysfs();
    	if (ret)
    		return ret;
    
    	if (ctrlval != cpu_smt_control) {
    		switch (ctrlval) {
    		case CPU_SMT_ENABLED:
    			ret = cpuhp_smt_enable();
    			break;
    		case CPU_SMT_DISABLED:
    		case CPU_SMT_FORCE_DISABLED:
    			ret = cpuhp_smt_disable(ctrlval);
    			break;
    		}
    	}
    
    	unlock_device_hotplug();
    	return ret ? ret : count;
    }
    
    #else /* !CONFIG_HOTPLUG_SMT */
    static ssize_t
    __store_smt_control(struct device *dev, struct device_attribute *attr,
    		    const char *buf, size_t count)
    {
    	return -ENODEV;
    }
    #endif /* CONFIG_HOTPLUG_SMT */
    
    static const char *smt_states[] = {
    	[CPU_SMT_ENABLED]		= "on",
    	[CPU_SMT_DISABLED]		= "off",
    	[CPU_SMT_FORCE_DISABLED]	= "forceoff",
    	[CPU_SMT_NOT_SUPPORTED]		= "notsupported",
    	[CPU_SMT_NOT_IMPLEMENTED]	= "notimplemented",
    };
    
    static ssize_t
    show_smt_control(struct device *dev, struct device_attribute *attr, char *buf)
    {
    	const char *state = smt_states[cpu_smt_control];
    
    	return snprintf(buf, PAGE_SIZE - 2, "%s\n", state);
    }
    
    static ssize_t
    store_smt_control(struct device *dev, struct device_attribute *attr,
    		  const char *buf, size_t count)
    {
    	return __store_smt_control(dev, attr, buf, count);
    }
    static DEVICE_ATTR(control, 0644, show_smt_control, store_smt_control);
    
    static ssize_t
    show_smt_active(struct device *dev, struct device_attribute *attr, char *buf)
    {
    	return snprintf(buf, PAGE_SIZE - 2, "%d\n", sched_smt_active());
    }
    static DEVICE_ATTR(active, 0444, show_smt_active, NULL);
    
    static struct attribute *cpuhp_smt_attrs[] = {
    	&dev_attr_control.attr,
    	&dev_attr_active.attr,
    	NULL
    };
    
    static const struct attribute_group cpuhp_smt_attr_group = {
    	.attrs = cpuhp_smt_attrs,
    	.name = "smt",
    	NULL
    };
    
    static int __init cpu_smt_sysfs_init(void)
    {
    	return sysfs_create_group(&cpu_subsys.dev_root->kobj,
    				  &cpuhp_smt_attr_group);
    }
    
    static int __init cpuhp_sysfs_init(void)
    {
    	int cpu, ret;
    
    	ret = cpu_smt_sysfs_init();
    	if (ret)
    		return ret;
    
    	ret = sysfs_create_group(&cpu_subsys.dev_root->kobj,
    				 &cpuhp_cpu_root_attr_group);
    	if (ret)
    		return ret;
    
    	for_each_possible_cpu(cpu) {
    		struct device *dev = get_cpu_device(cpu);
    
    		if (!dev)
    			continue;
    		ret = sysfs_create_group(&dev->kobj, &cpuhp_cpu_attr_group);
    		if (ret)
    			return ret;
    	}
    	return 0;
    }
    device_initcall(cpuhp_sysfs_init);
    #endif /* CONFIG_SYSFS && CONFIG_HOTPLUG_CPU */
    
    /*
     * cpu_bit_bitmap[] is a special, "compressed" data structure that
     * represents all NR_CPUS bits binary values of 1<<nr.
     *
     * It is used by cpumask_of() to get a constant address to a CPU
     * mask value that has a single bit set only.
     */
    
    /* cpu_bit_bitmap[0] is empty - so we can back into it */
    #define MASK_DECLARE_1(x)	[x+1][0] = (1UL << (x))
    #define MASK_DECLARE_2(x)	MASK_DECLARE_1(x), MASK_DECLARE_1(x+1)
    #define MASK_DECLARE_4(x)	MASK_DECLARE_2(x), MASK_DECLARE_2(x+2)
    #define MASK_DECLARE_8(x)	MASK_DECLARE_4(x), MASK_DECLARE_4(x+4)
    
    const unsigned long cpu_bit_bitmap[BITS_PER_LONG+1][BITS_TO_LONGS(NR_CPUS)] = {
    
    	MASK_DECLARE_8(0),	MASK_DECLARE_8(8),
    	MASK_DECLARE_8(16),	MASK_DECLARE_8(24),
    #if BITS_PER_LONG > 32
    	MASK_DECLARE_8(32),	MASK_DECLARE_8(40),
    	MASK_DECLARE_8(48),	MASK_DECLARE_8(56),
    #endif
    };
    EXPORT_SYMBOL_GPL(cpu_bit_bitmap);
    
    const DECLARE_BITMAP(cpu_all_bits, NR_CPUS) = CPU_BITS_ALL;
    EXPORT_SYMBOL(cpu_all_bits);
    
    #ifdef CONFIG_INIT_ALL_POSSIBLE
    struct cpumask __cpu_possible_mask __read_mostly
    	= {CPU_BITS_ALL};
    #else
    struct cpumask __cpu_possible_mask __read_mostly;
    #endif
    EXPORT_SYMBOL(__cpu_possible_mask);
    
    struct cpumask __cpu_online_mask __read_mostly;
    EXPORT_SYMBOL(__cpu_online_mask);
    
    struct cpumask __cpu_present_mask __read_mostly;
    EXPORT_SYMBOL(__cpu_present_mask);
    
    struct cpumask __cpu_active_mask __read_mostly;
    EXPORT_SYMBOL(__cpu_active_mask);
    
    atomic_t __num_online_cpus __read_mostly;
    EXPORT_SYMBOL(__num_online_cpus);
    
    void init_cpu_present(const struct cpumask *src)
    {
    	cpumask_copy(&__cpu_present_mask, src);
    }
    
    void init_cpu_possible(const struct cpumask *src)
    {
    	cpumask_copy(&__cpu_possible_mask, src);
    }
    
    void init_cpu_online(const struct cpumask *src)
    {
    	cpumask_copy(&__cpu_online_mask, src);
    }
    
    void set_cpu_online(unsigned int cpu, bool online)
    {
    	/*
    	 * atomic_inc/dec() is required to handle the horrid abuse of this
    	 * function by the reboot and kexec code which invoke it from
    	 * IPI/NMI broadcasts when shutting down CPUs. Invocation from
    	 * regular CPU hotplug is properly serialized.
    	 *
    	 * Note, that the fact that __num_online_cpus is of type atomic_t
    	 * does not protect readers which are not serialized against
    	 * concurrent hotplug operations.
    	 */
    	if (online) {
    		if (!cpumask_test_and_set_cpu(cpu, &__cpu_online_mask))
    			atomic_inc(&__num_online_cpus);
    	} else {
    		if (cpumask_test_and_clear_cpu(cpu, &__cpu_online_mask))
    			atomic_dec(&__num_online_cpus);
    	}
    }
    
    /*
     * Activate the first processor.
     */
    void __init boot_cpu_init(void)
    {
    	int cpu = smp_processor_id();
    
    	/* Mark the boot cpu "present", "online" etc for SMP and UP case */
    	set_cpu_online(cpu, true);
    	set_cpu_active(cpu, true);
    	set_cpu_present(cpu, true);
    	set_cpu_possible(cpu, true);
    
    #ifdef CONFIG_SMP
    	__boot_cpu_id = cpu;
    #endif
    }
    
    /*
     * Must be called _AFTER_ setting up the per_cpu areas
     */
    void __init boot_cpu_hotplug_init(void)
    {
    #ifdef CONFIG_SMP
    	cpumask_set_cpu(smp_processor_id(), &cpus_booted_once_mask);
    #endif
    	this_cpu_write(cpuhp_state.state, CPUHP_ONLINE);
    }
    
    /*
     * These are used for a global "mitigations=" cmdline option for toggling
     * optional CPU mitigations.
     */
    enum cpu_mitigations {
    	CPU_MITIGATIONS_OFF,
    	CPU_MITIGATIONS_AUTO,
    	CPU_MITIGATIONS_AUTO_NOSMT,
    };
    
    static enum cpu_mitigations cpu_mitigations __ro_after_init =
    	CPU_MITIGATIONS_AUTO;
    
    static int __init mitigations_parse_cmdline(char *arg)
    {
    	if (!strcmp(arg, "off"))
    		cpu_mitigations = CPU_MITIGATIONS_OFF;
    	else if (!strcmp(arg, "auto"))
    		cpu_mitigations = CPU_MITIGATIONS_AUTO;
    	else if (!strcmp(arg, "auto,nosmt"))
    		cpu_mitigations = CPU_MITIGATIONS_AUTO_NOSMT;
    	else
    		pr_crit("Unsupported mitigations=%s, system may still be vulnerable\n",
    			arg);
    
    	return 0;
    }
    early_param("mitigations", mitigations_parse_cmdline);
    
    /* mitigations=off */
    bool cpu_mitigations_off(void)
    {
    	return cpu_mitigations == CPU_MITIGATIONS_OFF;
    }
    EXPORT_SYMBOL_GPL(cpu_mitigations_off);
    
    /* mitigations=auto,nosmt */
    bool cpu_mitigations_auto_nosmt(void)
    {
    	return cpu_mitigations == CPU_MITIGATIONS_AUTO_NOSMT;
    }
    EXPORT_SYMBOL_GPL(cpu_mitigations_auto_nosmt);