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    Subject[PATCH 1/9 V3] workqueue: ensure the wq_worker_sleeping() see the right flags
    Date
    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 use one write/modify instruction explicitly instead.

    This bug will not occur on idle workers, because they have another
    WORKER_NOT_RUNNING flags.

    Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
    ---
    kernel/workqueue.c | 7 +++++--
    1 files changed, 5 insertions(+), 2 deletions(-)

    diff --git a/kernel/workqueue.c b/kernel/workqueue.c
    index 692d976..4f252d0 100644
    --- a/kernel/workqueue.c
    +++ b/kernel/workqueue.c
    @@ -1434,10 +1434,13 @@ retry:
    /* rebind busy workers */
    for_each_busy_worker(worker, i, pos, gcwq) {
    struct work_struct *rebind_work = &worker->rebind_work;
    + unsigned long worker_flags = worker->flags;

    /* morph UNBOUND to REBIND */
    - worker->flags &= ~WORKER_UNBOUND;
    - worker->flags |= WORKER_REBIND;
    + worker_flags &= ~WORKER_UNBOUND;
    + worker_flags |= WORKER_REBIND;
    + /* ensure the wq_worker_sleeping() see the right flags */
    + ACCESS_ONCE(worker->flags) = worker_flags;

    if (test_and_set_bit(WORK_STRUCT_PENDING_BIT,
    work_data_bits(rebind_work)))
    --
    1.7.4.4


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