• Peter Zijlstra's avatar
    workqueue: Fix setting affinity of unbound worker threads · d945b5e9
    Peter Zijlstra authored
    With commit e9d867a6
    
     ("sched: Allow per-cpu kernel threads to
    run on online && !active"), __set_cpus_allowed_ptr() expects that only
    strict per-cpu kernel threads can have affinity to an online CPU which
    is not yet active.
    
    This assumption is currently broken in the CPU_ONLINE notification
    handler for the workqueues where restore_unbound_workers_cpumask()
    calls set_cpus_allowed_ptr() when the first cpu in the unbound
    worker's pool->attr->cpumask comes online. Since
    set_cpus_allowed_ptr() is called with pool->attr->cpumask in which
    only one CPU is online which is not yet active, we get the following
    WARN_ON during an CPU online operation.
    
    ------------[ cut here ]------------
    WARNING: CPU: 40 PID: 248 at kernel/sched/core.c:1166
    __set_cpus_allowed_ptr+0x228/0x2e0
    Modules linked in:
    CPU: 40 PID: 248 Comm: cpuhp/40 Not tainted 4.6.0-autotest+ #4
    <..snip..>
    Call Trace:
    [c000000f273ff920] [c00000000010493c] __set_cpus_allowed_ptr+0x2cc/0x2e0 (unreliable)
    [c000000f273ffac0] [c0000000000ed4b0] workqueue_cpu_up_callback+0x2c0/0x470
    [c000000f273ffb70] [c0000000000f5c58] notifier_call_chain+0x98/0x100
    [c000000f273ffbc0] [c0000000000c5ed0] __cpu_notify+0x70/0xe0
    [c000000f273ffc00] [c0000000000c6028] notify_online+0x38/0x50
    [c000000f273ffc30] [c0000000000c5214] cpuhp_invoke_callback+0x84/0x250
    [c000000f273ffc90] [c0000000000c562c] cpuhp_up_callbacks+0x5c/0x120
    [c000000f273ffce0] [c0000000000c64d4] cpuhp_thread_fun+0x184/0x1c0
    [c000000f273ffd20] [c0000000000fa050] smpboot_thread_fn+0x290/0x2a0
    [c000000f273ffd80] [c0000000000f45b0] kthread+0x110/0x130
    [c000000f273ffe30] [c000000000009570] ret_from_kernel_thread+0x5c/0x6c
    ---[ end trace 00f1456578b2a3b2 ]---
    
    This patch fixes this by limiting the mask to the intersection of
    the pool affinity and online CPUs.
    
    Changelog-cribbed-from: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
    Reported-by: default avatarAbdul Haleem <abdhalee@linux.vnet.ibm.com>
    Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
    Signed-off-by: default avatarTejun Heo <tj@kernel.org>
    d945b5e9
workqueue.c 153 KB