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    sched: adjust when cpu_active and cpuset configurations are updated during cpu on/offlining · 3a101d05
    Tejun Heo 提交于
    Currently, when a cpu goes down, cpu_active is cleared before
    CPU_DOWN_PREPARE starts and cpuset configuration is updated from a
    default priority cpu notifier.  When a cpu is coming up, it's set
    before CPU_ONLINE but cpuset configuration again is updated from the
    same cpu notifier.
    
    For cpu notifiers, this presents an inconsistent state.  Threads which
    a CPU_DOWN_PREPARE notifier expects to be bound to the CPU can be
    migrated to other cpus because the cpu is no more inactive.
    
    Fix it by updating cpu_active in the highest priority cpu notifier and
    cpuset configuration in the second highest when a cpu is coming up.
    Down path is updated similarly.  This guarantees that all other cpu
    notifiers see consistent cpu_active and cpuset configuration.
    
    cpuset_track_online_cpus() notifier is converted to
    cpuset_update_active_cpus() which just updates the configuration and
    now called from cpuset_cpu_[in]active() notifiers registered from
    sched_init_smp().  If cpuset is disabled, cpuset_update_active_cpus()
    degenerates into partition_sched_domains() making separate notifier
    for !CONFIG_CPUSETS unnecessary.
    
    This problem is triggered by cmwq.  During CPU_DOWN_PREPARE, hotplug
    callback creates a kthread and kthread_bind()s it to the target cpu,
    and the thread is expected to run on that cpu.
    
    * Ingo's test discovered __cpuinit/exit markups were incorrect.
      Fixed.
    Signed-off-by: NTejun Heo <tj@kernel.org>
    Acked-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: Rusty Russell <rusty@rustcorp.com.au>
    Cc: Ingo Molnar <mingo@elte.hu>
    Cc: Paul Menage <menage@google.com>
    3a101d05
cpu.h 5.0 KB