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32 results

segment.c

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  • oom_kill.c 30.33 KiB
    // SPDX-License-Identifier: GPL-2.0-only
    /*
     *  linux/mm/oom_kill.c
     * 
     *  Copyright (C)  1998,2000  Rik van Riel
     *	Thanks go out to Claus Fischer for some serious inspiration and
     *	for goading me into coding this file...
     *  Copyright (C)  2010  Google, Inc.
     *	Rewritten by David Rientjes
     *
     *  The routines in this file are used to kill a process when
     *  we're seriously out of memory. This gets called from __alloc_pages()
     *  in mm/page_alloc.c when we really run out of memory.
     *
     *  Since we won't call these routines often (on a well-configured
     *  machine) this file will double as a 'coding guide' and a signpost
     *  for newbie kernel hackers. It features several pointers to major
     *  kernel subsystems and hints as to where to find out what things do.
     */
    
    #include <linux/oom.h>
    #include <linux/mm.h>
    #include <linux/err.h>
    #include <linux/gfp.h>
    #include <linux/sched.h>
    #include <linux/sched/mm.h>
    #include <linux/sched/coredump.h>
    #include <linux/sched/task.h>
    #include <linux/sched/debug.h>
    #include <linux/swap.h>
    #include <linux/timex.h>
    #include <linux/jiffies.h>
    #include <linux/cpuset.h>
    #include <linux/export.h>
    #include <linux/notifier.h>
    #include <linux/memcontrol.h>
    #include <linux/mempolicy.h>
    #include <linux/security.h>
    #include <linux/ptrace.h>
    #include <linux/freezer.h>
    #include <linux/ftrace.h>
    #include <linux/ratelimit.h>
    #include <linux/kthread.h>
    #include <linux/init.h>
    #include <linux/mmu_notifier.h>
    
    #include <asm/tlb.h>
    #include "internal.h"
    #include "slab.h"
    
    #define CREATE_TRACE_POINTS
    #include <trace/events/oom.h>
    
    int sysctl_panic_on_oom;
    int sysctl_oom_kill_allocating_task;
    int sysctl_oom_dump_tasks = 1;
    
    /*
     * Serializes oom killer invocations (out_of_memory()) from all contexts to
     * prevent from over eager oom killing (e.g. when the oom killer is invoked
     * from different domains).
     *
     * oom_killer_disable() relies on this lock to stabilize oom_killer_disabled
     * and mark_oom_victim
     */
    DEFINE_MUTEX(oom_lock);
    /* Serializes oom_score_adj and oom_score_adj_min updates */
    DEFINE_MUTEX(oom_adj_mutex);
    
    static inline bool is_memcg_oom(struct oom_control *oc)
    {
    	return oc->memcg != NULL;
    }
    
    #ifdef CONFIG_NUMA
    /**
     * oom_cpuset_eligible() - check task eligiblity for kill
     * @start: task struct of which task to consider
     * @oc: pointer to struct oom_control
     *
     * Task eligibility is determined by whether or not a candidate task, @tsk,
     * shares the same mempolicy nodes as current if it is bound by such a policy
     * and whether or not it has the same set of allowed cpuset nodes.
     *
     * This function is assuming oom-killer context and 'current' has triggered
     * the oom-killer.
     */
    static bool oom_cpuset_eligible(struct task_struct *start,
    				struct oom_control *oc)
    {
    	struct task_struct *tsk;
    	bool ret = false;
    	const nodemask_t *mask = oc->nodemask;
    
    	if (is_memcg_oom(oc))
    		return true;
    
    	rcu_read_lock();
    	for_each_thread(start, tsk) {
    		if (mask) {
    			/*
    			 * If this is a mempolicy constrained oom, tsk's
    			 * cpuset is irrelevant.  Only return true if its
    			 * mempolicy intersects current, otherwise it may be
    			 * needlessly killed.
    			 */
    			ret = mempolicy_nodemask_intersects(tsk, mask);
    		} else {
    			/*
    			 * This is not a mempolicy constrained oom, so only
    			 * check the mems of tsk's cpuset.
    			 */
    			ret = cpuset_mems_allowed_intersects(current, tsk);
    		}
    		if (ret)
    			break;
    	}
    	rcu_read_unlock();
    
    	return ret;
    }
    #else
    static bool oom_cpuset_eligible(struct task_struct *tsk, struct oom_control *oc)
    {
    	return true;
    }
    #endif /* CONFIG_NUMA */
    
    /*
     * The process p may have detached its own ->mm while exiting or through
     * kthread_use_mm(), but one or more of its subthreads may still have a valid
     * pointer.  Return p, or any of its subthreads with a valid ->mm, with
     * task_lock() held.
     */
    struct task_struct *find_lock_task_mm(struct task_struct *p)
    {
    	struct task_struct *t;
    
    	rcu_read_lock();
    
    	for_each_thread(p, t) {
    		task_lock(t);
    		if (likely(t->mm))
    			goto found;
    		task_unlock(t);
    	}
    	t = NULL;
    found:
    	rcu_read_unlock();
    
    	return t;
    }
    
    /*
     * order == -1 means the oom kill is required by sysrq, otherwise only
     * for display purposes.
     */
    static inline bool is_sysrq_oom(struct oom_control *oc)
    {
    	return oc->order == -1;
    }
    
    /* return true if the task is not adequate as candidate victim task. */
    static bool oom_unkillable_task(struct task_struct *p)
    {
    	if (is_global_init(p))
    		return true;
    	if (p->flags & PF_KTHREAD)
    		return true;
    	return false;
    }
    
    /**
     * Check whether unreclaimable slab amount is greater than
     * all user memory(LRU pages).
     * dump_unreclaimable_slab() could help in the case that
     * oom due to too much unreclaimable slab used by kernel.
    */
    static bool should_dump_unreclaim_slab(void)
    {
    	unsigned long nr_lru;
    
    	nr_lru = global_node_page_state(NR_ACTIVE_ANON) +
    		 global_node_page_state(NR_INACTIVE_ANON) +
    		 global_node_page_state(NR_ACTIVE_FILE) +
    		 global_node_page_state(NR_INACTIVE_FILE) +
    		 global_node_page_state(NR_ISOLATED_ANON) +
    		 global_node_page_state(NR_ISOLATED_FILE) +
    		 global_node_page_state(NR_UNEVICTABLE);
    
    	return (global_node_page_state_pages(NR_SLAB_UNRECLAIMABLE_B) > nr_lru);
    }
    
    /**
     * oom_badness - heuristic function to determine which candidate task to kill
     * @p: task struct of which task we should calculate
     * @totalpages: total present RAM allowed for page allocation
     *
     * The heuristic for determining which task to kill is made to be as simple and
     * predictable as possible.  The goal is to return the highest value for the
     * task consuming the most memory to avoid subsequent oom failures.
     */
    long oom_badness(struct task_struct *p, unsigned long totalpages)
    {
    	long points;
    	long adj;
    
    	if (oom_unkillable_task(p))
    		return LONG_MIN;
    
    	p = find_lock_task_mm(p);
    	if (!p)
    		return LONG_MIN;
    
    	/*
    	 * Do not even consider tasks which are explicitly marked oom
    	 * unkillable or have been already oom reaped or the are in
    	 * the middle of vfork
    	 */
    	adj = (long)p->signal->oom_score_adj;
    	if (adj == OOM_SCORE_ADJ_MIN ||
    			test_bit(MMF_OOM_SKIP, &p->mm->flags) ||
    			in_vfork(p)) {
    		task_unlock(p);
    		return LONG_MIN;
    	}
    
    	/*
    	 * The baseline for the badness score is the proportion of RAM that each
    	 * task's rss, pagetable and swap space use.
    	 */
    	points = get_mm_rss(p->mm) + get_mm_counter(p->mm, MM_SWAPENTS) +
    		mm_pgtables_bytes(p->mm) / PAGE_SIZE;
    	task_unlock(p);
    
    	/* Normalize to oom_score_adj units */
    	adj *= totalpages / 1000;
    	points += adj;
    
    	return points;
    }
    
    static const char * const oom_constraint_text[] = {
    	[CONSTRAINT_NONE] = "CONSTRAINT_NONE",
    	[CONSTRAINT_CPUSET] = "CONSTRAINT_CPUSET",
    	[CONSTRAINT_MEMORY_POLICY] = "CONSTRAINT_MEMORY_POLICY",
    	[CONSTRAINT_MEMCG] = "CONSTRAINT_MEMCG",
    };
    
    /*
     * Determine the type of allocation constraint.
     */
    static enum oom_constraint constrained_alloc(struct oom_control *oc)
    {
    	struct zone *zone;
    	struct zoneref *z;
    	enum zone_type highest_zoneidx = gfp_zone(oc->gfp_mask);
    	bool cpuset_limited = false;
    	int nid;
    
    	if (is_memcg_oom(oc)) {
    		oc->totalpages = mem_cgroup_get_max(oc->memcg) ?: 1;
    		return CONSTRAINT_MEMCG;
    	}
    
    	/* Default to all available memory */
    	oc->totalpages = totalram_pages() + total_swap_pages;
    
    	if (!IS_ENABLED(CONFIG_NUMA))
    		return CONSTRAINT_NONE;
    
    	if (!oc->zonelist)
    		return CONSTRAINT_NONE;
    	/*
    	 * Reach here only when __GFP_NOFAIL is used. So, we should avoid
    	 * to kill current.We have to random task kill in this case.
    	 * Hopefully, CONSTRAINT_THISNODE...but no way to handle it, now.
    	 */
    	if (oc->gfp_mask & __GFP_THISNODE)
    		return CONSTRAINT_NONE;
    
    	/*
    	 * This is not a __GFP_THISNODE allocation, so a truncated nodemask in
    	 * the page allocator means a mempolicy is in effect.  Cpuset policy
    	 * is enforced in get_page_from_freelist().
    	 */
    	if (oc->nodemask &&
    	    !nodes_subset(node_states[N_MEMORY], *oc->nodemask)) {
    		oc->totalpages = total_swap_pages;
    		for_each_node_mask(nid, *oc->nodemask)
    			oc->totalpages += node_present_pages(nid);
    		return CONSTRAINT_MEMORY_POLICY;
    	}
    
    	/* Check this allocation failure is caused by cpuset's wall function */
    	for_each_zone_zonelist_nodemask(zone, z, oc->zonelist,
    			highest_zoneidx, oc->nodemask)
    		if (!cpuset_zone_allowed(zone, oc->gfp_mask))
    			cpuset_limited = true;
    
    	if (cpuset_limited) {
    		oc->totalpages = total_swap_pages;
    		for_each_node_mask(nid, cpuset_current_mems_allowed)
    			oc->totalpages += node_present_pages(nid);
    		return CONSTRAINT_CPUSET;
    	}
    	return CONSTRAINT_NONE;
    }
    
    static int oom_evaluate_task(struct task_struct *task, void *arg)
    {
    	struct oom_control *oc = arg;
    	long points;
    
    	if (oom_unkillable_task(task))
    		goto next;
    
    	/* p may not have freeable memory in nodemask */
    	if (!is_memcg_oom(oc) && !oom_cpuset_eligible(task, oc))
    		goto next;
    
    	/*
    	 * This task already has access to memory reserves and is being killed.
    	 * Don't allow any other task to have access to the reserves unless
    	 * the task has MMF_OOM_SKIP because chances that it would release
    	 * any memory is quite low.
    	 */
    	if (!is_sysrq_oom(oc) && tsk_is_oom_victim(task)) {
    		if (test_bit(MMF_OOM_SKIP, &task->signal->oom_mm->flags))
    			goto next;
    		goto abort;
    	}
    
    	/*
    	 * If task is allocating a lot of memory and has been marked to be
    	 * killed first if it triggers an oom, then select it.
    	 */
    	if (oom_task_origin(task)) {
    		points = LONG_MAX;
    		goto select;
    	}
    
    	points = oom_badness(task, oc->totalpages);
    	if (points == LONG_MIN || points < oc->chosen_points)
    		goto next;
    
    select:
    	if (oc->chosen)
    		put_task_struct(oc->chosen);
    	get_task_struct(task);
    	oc->chosen = task;
    	oc->chosen_points = points;
    next:
    	return 0;
    abort:
    	if (oc->chosen)
    		put_task_struct(oc->chosen);
    	oc->chosen = (void *)-1UL;
    	return 1;
    }
    
    /*
     * Simple selection loop. We choose the process with the highest number of
     * 'points'. In case scan was aborted, oc->chosen is set to -1.
     */
    static void select_bad_process(struct oom_control *oc)
    {
    	oc->chosen_points = LONG_MIN;
    
    	if (is_memcg_oom(oc))
    		mem_cgroup_scan_tasks(oc->memcg, oom_evaluate_task, oc);
    	else {
    		struct task_struct *p;
    
    		rcu_read_lock();
    		for_each_process(p)
    			if (oom_evaluate_task(p, oc))
    				break;
    		rcu_read_unlock();
    	}
    }
    
    static int dump_task(struct task_struct *p, void *arg)
    {
    	struct oom_control *oc = arg;
    	struct task_struct *task;
    
    	if (oom_unkillable_task(p))
    		return 0;
    
    	/* p may not have freeable memory in nodemask */
    	if (!is_memcg_oom(oc) && !oom_cpuset_eligible(p, oc))
    		return 0;
    
    	task = find_lock_task_mm(p);
    	if (!task) {
    		/*
    		 * All of p's threads have already detached their mm's. There's
    		 * no need to report them; they can't be oom killed anyway.
    		 */
    		return 0;
    	}
    
    	pr_info("[%7d] %5d %5d %8lu %8lu %8ld %8lu         %5hd %s\n",
    		task->pid, from_kuid(&init_user_ns, task_uid(task)),
    		task->tgid, task->mm->total_vm, get_mm_rss(task->mm),
    		mm_pgtables_bytes(task->mm),
    		get_mm_counter(task->mm, MM_SWAPENTS),
    		task->signal->oom_score_adj, task->comm);
    	task_unlock(task);
    
    	return 0;
    }
    
    /**
     * dump_tasks - dump current memory state of all system tasks
     * @oc: pointer to struct oom_control
     *
     * Dumps the current memory state of all eligible tasks.  Tasks not in the same
     * memcg, not in the same cpuset, or bound to a disjoint set of mempolicy nodes
     * are not shown.
     * State information includes task's pid, uid, tgid, vm size, rss,
     * pgtables_bytes, swapents, oom_score_adj value, and name.
     */
    static void dump_tasks(struct oom_control *oc)
    {
    	pr_info("Tasks state (memory values in pages):\n");
    	pr_info("[  pid  ]   uid  tgid total_vm      rss pgtables_bytes swapents oom_score_adj name\n");
    
    	if (is_memcg_oom(oc))
    		mem_cgroup_scan_tasks(oc->memcg, dump_task, oc);
    	else {
    		struct task_struct *p;
    
    		rcu_read_lock();
    		for_each_process(p)
    			dump_task(p, oc);
    		rcu_read_unlock();
    	}
    }
    
    static void dump_oom_summary(struct oom_control *oc, struct task_struct *victim)
    {
    	/* one line summary of the oom killer context. */
    	pr_info("oom-kill:constraint=%s,nodemask=%*pbl",
    			oom_constraint_text[oc->constraint],
    			nodemask_pr_args(oc->nodemask));
    	cpuset_print_current_mems_allowed();
    	mem_cgroup_print_oom_context(oc->memcg, victim);
    	pr_cont(",task=%s,pid=%d,uid=%d\n", victim->comm, victim->pid,
    		from_kuid(&init_user_ns, task_uid(victim)));
    }
    
    static void dump_header(struct oom_control *oc, struct task_struct *p)
    {
    	pr_warn("%s invoked oom-killer: gfp_mask=%#x(%pGg), order=%d, oom_score_adj=%hd\n",
    		current->comm, oc->gfp_mask, &oc->gfp_mask, oc->order,
    			current->signal->oom_score_adj);
    	if (!IS_ENABLED(CONFIG_COMPACTION) && oc->order)
    		pr_warn("COMPACTION is disabled!!!\n");
    
    	dump_stack();
    	if (is_memcg_oom(oc))
    		mem_cgroup_print_oom_meminfo(oc->memcg);
    	else {
    		show_mem(SHOW_MEM_FILTER_NODES, oc->nodemask);
    		if (should_dump_unreclaim_slab())
    			dump_unreclaimable_slab();
    	}
    	if (sysctl_oom_dump_tasks)
    		dump_tasks(oc);
    	if (p)
    		dump_oom_summary(oc, p);
    }
    
    /*
     * Number of OOM victims in flight
     */
    static atomic_t oom_victims = ATOMIC_INIT(0);
    static DECLARE_WAIT_QUEUE_HEAD(oom_victims_wait);
    
    static bool oom_killer_disabled __read_mostly;
    
    #define K(x) ((x) << (PAGE_SHIFT-10))
    
    /*
     * task->mm can be NULL if the task is the exited group leader.  So to
     * determine whether the task is using a particular mm, we examine all the
     * task's threads: if one of those is using this mm then this task was also
     * using it.
     */
    bool process_shares_mm(struct task_struct *p, struct mm_struct *mm)
    {
    	struct task_struct *t;
    
    	for_each_thread(p, t) {
    		struct mm_struct *t_mm = READ_ONCE(t->mm);
    		if (t_mm)
    			return t_mm == mm;
    	}
    	return false;
    }
    
    #ifdef CONFIG_MMU
    /*
     * OOM Reaper kernel thread which tries to reap the memory used by the OOM
     * victim (if that is possible) to help the OOM killer to move on.
     */
    static struct task_struct *oom_reaper_th;
    static DECLARE_WAIT_QUEUE_HEAD(oom_reaper_wait);
    static struct task_struct *oom_reaper_list;
    static DEFINE_SPINLOCK(oom_reaper_lock);
    
    bool __oom_reap_task_mm(struct mm_struct *mm)
    {
    	struct vm_area_struct *vma;
    	bool ret = true;
    
    	/*
    	 * Tell all users of get_user/copy_from_user etc... that the content
    	 * is no longer stable. No barriers really needed because unmapping
    	 * should imply barriers already and the reader would hit a page fault
    	 * if it stumbled over a reaped memory.
    	 */
    	set_bit(MMF_UNSTABLE, &mm->flags);
    
    	for (vma = mm->mmap ; vma; vma = vma->vm_next) {
    		if (!can_madv_lru_vma(vma))
    			continue;
    
    		/*
    		 * Only anonymous pages have a good chance to be dropped
    		 * without additional steps which we cannot afford as we
    		 * are OOM already.
    		 *
    		 * We do not even care about fs backed pages because all
    		 * which are reclaimable have already been reclaimed and
    		 * we do not want to block exit_mmap by keeping mm ref
    		 * count elevated without a good reason.
    		 */
    		if (vma_is_anonymous(vma) || !(vma->vm_flags & VM_SHARED)) {
    			struct mmu_notifier_range range;
    			struct mmu_gather tlb;
    
    			mmu_notifier_range_init(&range, MMU_NOTIFY_UNMAP, 0,
    						vma, mm, vma->vm_start,
    						vma->vm_end);
    			tlb_gather_mmu(&tlb, mm);
    			if (mmu_notifier_invalidate_range_start_nonblock(&range)) {
    				tlb_finish_mmu(&tlb);
    				ret = false;
    				continue;
    			}
    			unmap_page_range(&tlb, vma, range.start, range.end, NULL);
    			mmu_notifier_invalidate_range_end(&range);
    			tlb_finish_mmu(&tlb);
    		}
    	}
    
    	return ret;
    }
    
    /*
     * Reaps the address space of the give task.
     *
     * Returns true on success and false if none or part of the address space
     * has been reclaimed and the caller should retry later.
     */
    static bool oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
    {
    	bool ret = true;
    
    	if (!mmap_read_trylock(mm)) {
    		trace_skip_task_reaping(tsk->pid);
    		return false;
    	}
    
    	/*
    	 * MMF_OOM_SKIP is set by exit_mmap when the OOM reaper can't
    	 * work on the mm anymore. The check for MMF_OOM_SKIP must run
    	 * under mmap_lock for reading because it serializes against the
    	 * mmap_write_lock();mmap_write_unlock() cycle in exit_mmap().
    	 */
    	if (test_bit(MMF_OOM_SKIP, &mm->flags)) {
    		trace_skip_task_reaping(tsk->pid);
    		goto out_unlock;
    	}
    
    	trace_start_task_reaping(tsk->pid);
    
    	/* failed to reap part of the address space. Try again later */
    	ret = __oom_reap_task_mm(mm);
    	if (!ret)
    		goto out_finish;
    
    	pr_info("oom_reaper: reaped process %d (%s), now anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n",
    			task_pid_nr(tsk), tsk->comm,
    			K(get_mm_counter(mm, MM_ANONPAGES)),
    			K(get_mm_counter(mm, MM_FILEPAGES)),
    			K(get_mm_counter(mm, MM_SHMEMPAGES)));
    out_finish:
    	trace_finish_task_reaping(tsk->pid);
    out_unlock:
    	mmap_read_unlock(mm);
    
    	return ret;
    }
    
    #define MAX_OOM_REAP_RETRIES 10
    static void oom_reap_task(struct task_struct *tsk)
    {
    	int attempts = 0;
    	struct mm_struct *mm = tsk->signal->oom_mm;
    
    	/* Retry the mmap_read_trylock(mm) a few times */
    	while (attempts++ < MAX_OOM_REAP_RETRIES && !oom_reap_task_mm(tsk, mm))
    		schedule_timeout_idle(HZ/10);
    
    	if (attempts <= MAX_OOM_REAP_RETRIES ||
    	    test_bit(MMF_OOM_SKIP, &mm->flags))
    		goto done;
    
    	pr_info("oom_reaper: unable to reap pid:%d (%s)\n",
    		task_pid_nr(tsk), tsk->comm);
    	sched_show_task(tsk);
    	debug_show_all_locks();
    
    done:
    	tsk->oom_reaper_list = NULL;
    
    	/*
    	 * Hide this mm from OOM killer because it has been either reaped or
    	 * somebody can't call mmap_write_unlock(mm).
    	 */
    	set_bit(MMF_OOM_SKIP, &mm->flags);
    
    	/* Drop a reference taken by wake_oom_reaper */
    	put_task_struct(tsk);
    }
    
    static int oom_reaper(void *unused)
    {
    	while (true) {
    		struct task_struct *tsk = NULL;
    
    		wait_event_freezable(oom_reaper_wait, oom_reaper_list != NULL);
    		spin_lock(&oom_reaper_lock);
    		if (oom_reaper_list != NULL) {
    			tsk = oom_reaper_list;
    			oom_reaper_list = tsk->oom_reaper_list;
    		}
    		spin_unlock(&oom_reaper_lock);
    
    		if (tsk)
    			oom_reap_task(tsk);
    	}
    
    	return 0;
    }
    
    static void wake_oom_reaper(struct task_struct *tsk)
    {
    	/* mm is already queued? */
    	if (test_and_set_bit(MMF_OOM_REAP_QUEUED, &tsk->signal->oom_mm->flags))
    		return;
    
    	get_task_struct(tsk);
    
    	spin_lock(&oom_reaper_lock);
    	tsk->oom_reaper_list = oom_reaper_list;
    	oom_reaper_list = tsk;
    	spin_unlock(&oom_reaper_lock);
    	trace_wake_reaper(tsk->pid);
    	wake_up(&oom_reaper_wait);
    }
    
    static int __init oom_init(void)
    {
    	oom_reaper_th = kthread_run(oom_reaper, NULL, "oom_reaper");
    	return 0;
    }
    subsys_initcall(oom_init)
    #else
    static inline void wake_oom_reaper(struct task_struct *tsk)
    {
    }
    #endif /* CONFIG_MMU */
    
    /**
     * mark_oom_victim - mark the given task as OOM victim
     * @tsk: task to mark
     *
     * Has to be called with oom_lock held and never after
     * oom has been disabled already.
     *
     * tsk->mm has to be non NULL and caller has to guarantee it is stable (either
     * under task_lock or operate on the current).
     */
    static void mark_oom_victim(struct task_struct *tsk)
    {
    	struct mm_struct *mm = tsk->mm;
    
    	WARN_ON(oom_killer_disabled);
    	/* OOM killer might race with memcg OOM */
    	if (test_and_set_tsk_thread_flag(tsk, TIF_MEMDIE))
    		return;
    
    	/* oom_mm is bound to the signal struct life time. */
    	if (!cmpxchg(&tsk->signal->oom_mm, NULL, mm)) {
    		mmgrab(tsk->signal->oom_mm);
    		set_bit(MMF_OOM_VICTIM, &mm->flags);
    	}
    
    	/*
    	 * Make sure that the task is woken up from uninterruptible sleep
    	 * if it is frozen because OOM killer wouldn't be able to free
    	 * any memory and livelock. freezing_slow_path will tell the freezer
    	 * that TIF_MEMDIE tasks should be ignored.
    	 */
    	__thaw_task(tsk);
    	atomic_inc(&oom_victims);
    	trace_mark_victim(tsk->pid);
    }
    
    /**
     * exit_oom_victim - note the exit of an OOM victim
     */
    void exit_oom_victim(void)
    {
    	clear_thread_flag(TIF_MEMDIE);
    
    	if (!atomic_dec_return(&oom_victims))
    		wake_up_all(&oom_victims_wait);
    }
    
    /**
     * oom_killer_enable - enable OOM killer
     */
    void oom_killer_enable(void)
    {
    	oom_killer_disabled = false;
    	pr_info("OOM killer enabled.\n");
    }
    
    /**
     * oom_killer_disable - disable OOM killer
     * @timeout: maximum timeout to wait for oom victims in jiffies
     *
     * Forces all page allocations to fail rather than trigger OOM killer.
     * Will block and wait until all OOM victims are killed or the given
     * timeout expires.
     *
     * The function cannot be called when there are runnable user tasks because
     * the userspace would see unexpected allocation failures as a result. Any
     * new usage of this function should be consulted with MM people.
     *
     * Returns true if successful and false if the OOM killer cannot be
     * disabled.
     */
    bool oom_killer_disable(signed long timeout)
    {
    	signed long ret;
    
    	/*
    	 * Make sure to not race with an ongoing OOM killer. Check that the
    	 * current is not killed (possibly due to sharing the victim's memory).
    	 */
    	if (mutex_lock_killable(&oom_lock))
    		return false;
    	oom_killer_disabled = true;
    	mutex_unlock(&oom_lock);
    
    	ret = wait_event_interruptible_timeout(oom_victims_wait,
    			!atomic_read(&oom_victims), timeout);
    	if (ret <= 0) {
    		oom_killer_enable();
    		return false;
    	}
    	pr_info("OOM killer disabled.\n");
    
    	return true;
    }
    
    static inline bool __task_will_free_mem(struct task_struct *task)
    {
    	struct signal_struct *sig = task->signal;
    
    	/*
    	 * A coredumping process may sleep for an extended period in exit_mm(),
    	 * so the oom killer cannot assume that the process will promptly exit
    	 * and release memory.
    	 */
    	if (sig->flags & SIGNAL_GROUP_COREDUMP)
    		return false;
    
    	if (sig->flags & SIGNAL_GROUP_EXIT)
    		return true;
    
    	if (thread_group_empty(task) && (task->flags & PF_EXITING))
    		return true;
    
    	return false;
    }
    
    /*
     * Checks whether the given task is dying or exiting and likely to
     * release its address space. This means that all threads and processes
     * sharing the same mm have to be killed or exiting.
     * Caller has to make sure that task->mm is stable (hold task_lock or
     * it operates on the current).
     */
    static bool task_will_free_mem(struct task_struct *task)
    {
    	struct mm_struct *mm = task->mm;
    	struct task_struct *p;
    	bool ret = true;
    
    	/*
    	 * Skip tasks without mm because it might have passed its exit_mm and
    	 * exit_oom_victim. oom_reaper could have rescued that but do not rely
    	 * on that for now. We can consider find_lock_task_mm in future.
    	 */
    	if (!mm)
    		return false;
    
    	if (!__task_will_free_mem(task))
    		return false;
    
    	/*
    	 * This task has already been drained by the oom reaper so there are
    	 * only small chances it will free some more
    	 */
    	if (test_bit(MMF_OOM_SKIP, &mm->flags))
    		return false;
    
    	if (atomic_read(&mm->mm_users) <= 1)
    		return true;
    
    	/*
    	 * Make sure that all tasks which share the mm with the given tasks
    	 * are dying as well to make sure that a) nobody pins its mm and
    	 * b) the task is also reapable by the oom reaper.
    	 */
    	rcu_read_lock();
    	for_each_process(p) {
    		if (!process_shares_mm(p, mm))
    			continue;
    		if (same_thread_group(task, p))
    			continue;
    		ret = __task_will_free_mem(p);
    		if (!ret)
    			break;
    	}
    	rcu_read_unlock();
    
    	return ret;
    }
    
    static void __oom_kill_process(struct task_struct *victim, const char *message)
    {
    	struct task_struct *p;
    	struct mm_struct *mm;
    	bool can_oom_reap = true;
    
    	p = find_lock_task_mm(victim);
    	if (!p) {
    		pr_info("%s: OOM victim %d (%s) is already exiting. Skip killing the task\n",
    			message, task_pid_nr(victim), victim->comm);
    		put_task_struct(victim);
    		return;
    	} else if (victim != p) {
    		get_task_struct(p);
    		put_task_struct(victim);
    		victim = p;
    	}
    
    	/* Get a reference to safely compare mm after task_unlock(victim) */
    	mm = victim->mm;
    	mmgrab(mm);
    
    	/* Raise event before sending signal: task reaper must see this */
    	count_vm_event(OOM_KILL);
    	memcg_memory_event_mm(mm, MEMCG_OOM_KILL);
    
    	/*
    	 * We should send SIGKILL before granting access to memory reserves
    	 * in order to prevent the OOM victim from depleting the memory
    	 * reserves from the user space under its control.
    	 */
    	do_send_sig_info(SIGKILL, SEND_SIG_PRIV, victim, PIDTYPE_TGID);
    	mark_oom_victim(victim);
    	pr_err("%s: Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB, UID:%u pgtables:%lukB oom_score_adj:%hd\n",
    		message, task_pid_nr(victim), victim->comm, K(mm->total_vm),
    		K(get_mm_counter(mm, MM_ANONPAGES)),
    		K(get_mm_counter(mm, MM_FILEPAGES)),
    		K(get_mm_counter(mm, MM_SHMEMPAGES)),
    		from_kuid(&init_user_ns, task_uid(victim)),
    		mm_pgtables_bytes(mm) >> 10, victim->signal->oom_score_adj);
    	task_unlock(victim);
    
    	/*
    	 * Kill all user processes sharing victim->mm in other thread groups, if
    	 * any.  They don't get access to memory reserves, though, to avoid
    	 * depletion of all memory.  This prevents mm->mmap_lock livelock when an
    	 * oom killed thread cannot exit because it requires the semaphore and
    	 * its contended by another thread trying to allocate memory itself.
    	 * That thread will now get access to memory reserves since it has a
    	 * pending fatal signal.
    	 */
    	rcu_read_lock();
    	for_each_process(p) {
    		if (!process_shares_mm(p, mm))
    			continue;
    		if (same_thread_group(p, victim))
    			continue;
    		if (is_global_init(p)) {
    			can_oom_reap = false;
    			set_bit(MMF_OOM_SKIP, &mm->flags);
    			pr_info("oom killer %d (%s) has mm pinned by %d (%s)\n",
    					task_pid_nr(victim), victim->comm,
    					task_pid_nr(p), p->comm);
    			continue;
    		}
    		/*
    		 * No kthead_use_mm() user needs to read from the userspace so
    		 * we are ok to reap it.
    		 */
    		if (unlikely(p->flags & PF_KTHREAD))
    			continue;
    		do_send_sig_info(SIGKILL, SEND_SIG_PRIV, p, PIDTYPE_TGID);
    	}
    	rcu_read_unlock();
    
    	if (can_oom_reap)
    		wake_oom_reaper(victim);
    
    	mmdrop(mm);
    	put_task_struct(victim);
    }
    #undef K
    
    /*
     * Kill provided task unless it's secured by setting
     * oom_score_adj to OOM_SCORE_ADJ_MIN.
     */
    static int oom_kill_memcg_member(struct task_struct *task, void *message)
    {
    	if (task->signal->oom_score_adj != OOM_SCORE_ADJ_MIN &&
    	    !is_global_init(task)) {
    		get_task_struct(task);
    		__oom_kill_process(task, message);
    	}
    	return 0;
    }
    
    static void oom_kill_process(struct oom_control *oc, const char *message)
    {
    	struct task_struct *victim = oc->chosen;
    	struct mem_cgroup *oom_group;
    	static DEFINE_RATELIMIT_STATE(oom_rs, DEFAULT_RATELIMIT_INTERVAL,
    					      DEFAULT_RATELIMIT_BURST);
    
    	/*
    	 * If the task is already exiting, don't alarm the sysadmin or kill
    	 * its children or threads, just give it access to memory reserves
    	 * so it can die quickly
    	 */
    	task_lock(victim);
    	if (task_will_free_mem(victim)) {
    		mark_oom_victim(victim);
    		wake_oom_reaper(victim);
    		task_unlock(victim);
    		put_task_struct(victim);
    		return;
    	}
    	task_unlock(victim);
    
    	if (__ratelimit(&oom_rs))
    		dump_header(oc, victim);
    
    	/*
    	 * Do we need to kill the entire memory cgroup?
    	 * Or even one of the ancestor memory cgroups?
    	 * Check this out before killing the victim task.
    	 */
    	oom_group = mem_cgroup_get_oom_group(victim, oc->memcg);
    
    	__oom_kill_process(victim, message);
    
    	/*
    	 * If necessary, kill all tasks in the selected memory cgroup.
    	 */
    	if (oom_group) {
    		mem_cgroup_print_oom_group(oom_group);
    		mem_cgroup_scan_tasks(oom_group, oom_kill_memcg_member,
    				      (void*)message);
    		mem_cgroup_put(oom_group);
    	}
    }
    
    /*
     * Determines whether the kernel must panic because of the panic_on_oom sysctl.
     */
    static void check_panic_on_oom(struct oom_control *oc)
    {
    	if (likely(!sysctl_panic_on_oom))
    		return;
    	if (sysctl_panic_on_oom != 2) {
    		/*
    		 * panic_on_oom == 1 only affects CONSTRAINT_NONE, the kernel
    		 * does not panic for cpuset, mempolicy, or memcg allocation
    		 * failures.
    		 */
    		if (oc->constraint != CONSTRAINT_NONE)
    			return;
    	}
    	/* Do not panic for oom kills triggered by sysrq */
    	if (is_sysrq_oom(oc))
    		return;
    	dump_header(oc, NULL);
    	panic("Out of memory: %s panic_on_oom is enabled\n",
    		sysctl_panic_on_oom == 2 ? "compulsory" : "system-wide");
    }
    
    static BLOCKING_NOTIFIER_HEAD(oom_notify_list);
    
    int register_oom_notifier(struct notifier_block *nb)
    {
    	return blocking_notifier_chain_register(&oom_notify_list, nb);
    }
    EXPORT_SYMBOL_GPL(register_oom_notifier);
    
    int unregister_oom_notifier(struct notifier_block *nb)
    {
    	return blocking_notifier_chain_unregister(&oom_notify_list, nb);
    }
    EXPORT_SYMBOL_GPL(unregister_oom_notifier);
    
    /**
     * out_of_memory - kill the "best" process when we run out of memory
     * @oc: pointer to struct oom_control
     *
     * If we run out of memory, we have the choice between either
     * killing a random task (bad), letting the system crash (worse)
     * OR try to be smart about which process to kill. Note that we
     * don't have to be perfect here, we just have to be good.
     */
    bool out_of_memory(struct oom_control *oc)
    {
    	unsigned long freed = 0;
    
    	if (oom_killer_disabled)
    		return false;
    
    	if (!is_memcg_oom(oc)) {
    		blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
    		if (freed > 0)
    			/* Got some memory back in the last second. */
    			return true;
    	}
    
    	/*
    	 * If current has a pending SIGKILL or is exiting, then automatically
    	 * select it.  The goal is to allow it to allocate so that it may
    	 * quickly exit and free its memory.
    	 */
    	if (task_will_free_mem(current)) {
    		mark_oom_victim(current);
    		wake_oom_reaper(current);
    		return true;
    	}
    
    	/*
    	 * The OOM killer does not compensate for IO-less reclaim.
    	 * pagefault_out_of_memory lost its gfp context so we have to
    	 * make sure exclude 0 mask - all other users should have at least
    	 * ___GFP_DIRECT_RECLAIM to get here. But mem_cgroup_oom() has to
    	 * invoke the OOM killer even if it is a GFP_NOFS allocation.
    	 */
    	if (oc->gfp_mask && !(oc->gfp_mask & __GFP_FS) && !is_memcg_oom(oc))
    		return true;
    
    	/*
    	 * Check if there were limitations on the allocation (only relevant for
    	 * NUMA and memcg) that may require different handling.
    	 */
    	oc->constraint = constrained_alloc(oc);
    	if (oc->constraint != CONSTRAINT_MEMORY_POLICY)
    		oc->nodemask = NULL;
    	check_panic_on_oom(oc);
    
    	if (!is_memcg_oom(oc) && sysctl_oom_kill_allocating_task &&
    	    current->mm && !oom_unkillable_task(current) &&
    	    oom_cpuset_eligible(current, oc) &&
    	    current->signal->oom_score_adj != OOM_SCORE_ADJ_MIN) {
    		get_task_struct(current);
    		oc->chosen = current;
    		oom_kill_process(oc, "Out of memory (oom_kill_allocating_task)");
    		return true;
    	}
    
    	select_bad_process(oc);
    	/* Found nothing?!?! */
    	if (!oc->chosen) {
    		dump_header(oc, NULL);
    		pr_warn("Out of memory and no killable processes...\n");
    		/*
    		 * If we got here due to an actual allocation at the
    		 * system level, we cannot survive this and will enter
    		 * an endless loop in the allocator. Bail out now.
    		 */
    		if (!is_sysrq_oom(oc) && !is_memcg_oom(oc))
    			panic("System is deadlocked on memory\n");
    	}
    	if (oc->chosen && oc->chosen != (void *)-1UL)
    		oom_kill_process(oc, !is_memcg_oom(oc) ? "Out of memory" :
    				 "Memory cgroup out of memory");
    	return !!oc->chosen;
    }
    
    /*
     * The pagefault handler calls here because it is out of memory, so kill a
     * memory-hogging task. If oom_lock is held by somebody else, a parallel oom
     * killing is already in progress so do nothing.
     */
    void pagefault_out_of_memory(void)
    {
    	struct oom_control oc = {
    		.zonelist = NULL,
    		.nodemask = NULL,
    		.memcg = NULL,
    		.gfp_mask = 0,
    		.order = 0,
    	};
    
    	if (mem_cgroup_oom_synchronize(true))
    		return;
    
    	if (!mutex_trylock(&oom_lock))
    		return;
    	out_of_memory(&oc);
    	mutex_unlock(&oom_lock);
    }