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    Subject[PATCH 4.19 38/71] kthread_worker: prevent queuing delayed work from timer_fn when it is being canceled
    Date
    From: Zqiang <qiang.zhang@windriver.com>

    commit 6993d0fdbee0eb38bfac350aa016f65ad11ed3b1 upstream.

    There is a small race window when a delayed work is being canceled and
    the work still might be queued from the timer_fn:

    CPU0 CPU1
    kthread_cancel_delayed_work_sync()
    __kthread_cancel_work_sync()
    __kthread_cancel_work()
    work->canceling++;
    kthread_delayed_work_timer_fn()
    kthread_insert_work();

    BUG: kthread_insert_work() should not get called when work->canceling is
    set.

    Signed-off-by: Zqiang <qiang.zhang@windriver.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Reviewed-by: Petr Mladek <pmladek@suse.com>
    Acked-by: Tejun Heo <tj@kernel.org>
    Cc: <stable@vger.kernel.org>
    Link: https://lkml.kernel.org/r/20201014083030.16895-1-qiang.zhang@windriver.com
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    kernel/kthread.c | 3 ++-
    1 file changed, 2 insertions(+), 1 deletion(-)

    --- a/kernel/kthread.c
    +++ b/kernel/kthread.c
    @@ -863,7 +863,8 @@ void kthread_delayed_work_timer_fn(struc
    /* Move the work from worker->delayed_work_list. */
    WARN_ON_ONCE(list_empty(&work->node));
    list_del_init(&work->node);
    - kthread_insert_work(worker, work, &worker->work_list);
    + if (!work->canceling)
    + kthread_insert_work(worker, work, &worker->work_list);

    spin_unlock(&worker->lock);
    }

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