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    Subject[PATCH 2/3 V2] workqueue: ensure the wq_worker_sleeping() see the right flags
    The compiler may compile this code into TWO write/modify instructions.
    worker->flags &= ~WORKER_UNBOUND;
    worker->flags |= WORKER_REBIND;

    so the other CPU may see the temporary of worker->flags which has
    not WORKER_UNBOUND nor WORKER_REBIND, it will wrongly do local wake up.

    So we simply change the code that WORKER_UNBOUND is cleared in
    busy_worker_rebind_fn(), not in rebind_workers(). And REBIND is not
    used for busy_worker, busy_worker_rebind_fn() knows itself need
    to do rebind when it is called.

    Because the rebind_workers() will wait busy_worker_rebind_fn() to
    finish rebinding and clearing, the CPU can't be offline,
    busy_worker_rebind_fn() will not clear the wrong WORKER_UNBOUND.

    Signed-off-by: Lai Jiangshan <>
    kernel/workqueue.c | 6 +-----
    1 files changed, 1 insertions(+), 5 deletions(-)

    diff --git a/kernel/workqueue.c b/kernel/workqueue.c
    index 5f63883..3e0bd20 100644
    --- a/kernel/workqueue.c
    +++ b/kernel/workqueue.c
    @@ -1354,7 +1354,7 @@ static void busy_worker_rebind_fn(struct work_struct *work)

    /* CPU must be online at this point */
    - worker_clr_flags(worker, WORKER_REBIND);
    + worker_clr_flags(worker, WORKER_UNBOUND);

    /* all_cnt is only accessed by the bound CPU, don't need any lock */
    @@ -1420,10 +1420,6 @@ static void rebind_workers(struct global_cwq *gcwq)
    for_each_busy_worker(worker, i, pos, gcwq) {
    struct work_struct *rebind_work = &worker->rebind_work;

    - /* morph UNBOUND to REBIND */
    - worker->flags &= ~WORKER_UNBOUND;
    - worker->flags |= WORKER_REBIND;
    if (test_and_set_bit(WORK_STRUCT_PENDING_BIT,

     \ /
      Last update: 2012-08-28 14:21    [W:0.022 / U:1.048 seconds]
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