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    Subject[PATCH 5.5 083/151] workqueue: dont use wq_select_unbound_cpu() for bound works
    Date
    From: Hillf Danton <hdanton@sina.com>

    commit aa202f1f56960c60e7befaa0f49c72b8fa11b0a8 upstream.

    wq_select_unbound_cpu() is designed for unbound workqueues only, but
    it's wrongly called when using a bound workqueue too.

    Fixing this ensures work queued to a bound workqueue with
    cpu=WORK_CPU_UNBOUND always runs on the local CPU.

    Before, that would happen only if wq_unbound_cpumask happened to include
    it (likely almost always the case), or was empty, or we got lucky with
    forced round-robin placement. So restricting
    /sys/devices/virtual/workqueue/cpumask to a small subset of a machine's
    CPUs would cause some bound work items to run unexpectedly there.

    Fixes: ef557180447f ("workqueue: schedule WORK_CPU_UNBOUND work on wq_unbound_cpumask CPUs")
    Cc: stable@vger.kernel.org # v4.5+
    Signed-off-by: Hillf Danton <hdanton@sina.com>
    [dj: massage changelog]
    Signed-off-by: Daniel Jordan <daniel.m.jordan@oracle.com>
    Cc: Tejun Heo <tj@kernel.org>
    Cc: Lai Jiangshan <jiangshanlai@gmail.com>
    Cc: linux-kernel@vger.kernel.org
    Signed-off-by: Tejun Heo <tj@kernel.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    kernel/workqueue.c | 14 ++++++++------
    1 file changed, 8 insertions(+), 6 deletions(-)

    --- a/kernel/workqueue.c
    +++ b/kernel/workqueue.c
    @@ -1411,14 +1411,16 @@ static void __queue_work(int cpu, struct
    return;
    rcu_read_lock();
    retry:
    - if (req_cpu == WORK_CPU_UNBOUND)
    - cpu = wq_select_unbound_cpu(raw_smp_processor_id());
    -
    /* pwq which will be used unless @work is executing elsewhere */
    - if (!(wq->flags & WQ_UNBOUND))
    - pwq = per_cpu_ptr(wq->cpu_pwqs, cpu);
    - else
    + if (wq->flags & WQ_UNBOUND) {
    + if (req_cpu == WORK_CPU_UNBOUND)
    + cpu = wq_select_unbound_cpu(raw_smp_processor_id());
    pwq = unbound_pwq_by_node(wq, cpu_to_node(cpu));
    + } else {
    + if (req_cpu == WORK_CPU_UNBOUND)
    + cpu = raw_smp_processor_id();
    + pwq = per_cpu_ptr(wq->cpu_pwqs, cpu);
    + }

    /*
    * If @work was previously on a different pool, it might still be

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