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    SubjectRe: [PATCH 15/21] workqueue: remove worker_maybe_bind_and_lock()
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    On Thu, Mar 21, 2013 at 2:10 AM, Tejun Heo <tj@kernel.org> wrote:
    > On Wed, Mar 20, 2013 at 03:28:15AM +0800, Lai Jiangshan wrote:
    >> static struct worker *alloc_worker(void)
    >> {
    >> struct worker *worker;
    >> @@ -2326,7 +2262,8 @@ repeat:
    >> spin_unlock_irq(&wq_mayday_lock);
    >>
    >> /* migrate to the target cpu if possible */
    >> - worker_maybe_bind_and_lock(pool);
    >> + set_cpus_allowed_ptr(current, pool->attrs->cpumask);
    >> + spin_lock_irq(&pool->lock);
    >> rescuer->pool = pool;
    >
    > You can't do this. The CPU might go up between set_cpus_allowed_ptr()
    > and spin_lock_irq() and the rescuer can end up executing a work item
    > which was issued while the target CPU is up on the wrong CPU.


    Why it is wrong?
    It can be allowed if the wq has rescuer. (wq of work_on_cpu() don't has rescuer,
    it does not hurt to work_on_cpu() of something else.

    Actually it was allowed by recent patches.
    If a cpu is up while a rescuer do process_scheduled_workers(),
    all the later work item will be running the wrong CPU while
    the target CPU is up.(due to for_cpu_pool_workers() don't include
    active rescuer).

    I don't want to go back to make cpuhotplug nor rescuer_theread become
    complicated.
    so I prefer to allow work item can run on wrong cpu if the wq has rescuer.
    All just needs a comments.

    I guess you will agaist me...... let me rewrite it .....

    Thanks,
    Lai

    >
    > Thanks.
    >
    > --
    > tejun
    > --
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