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    Subject[PATCH 1/3] work_on_cpu: dont try to get_online_cpus() in work_on_cpu.
    From: Rusty Russell <rusty@rustcorp.com.au>

    Impact: remove potential circular lock dependency with cpu hotplug lock

    This has caused more problems than it solved, with a pile of cpu
    hotplug locking issues.

    Followup patches will get_online_cpus() in callers that need it, but
    if they don't do it they're no worse than before when they were using
    set_cpus_allowed without locking.

    Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
    Signed-off-by: Mike Travis <travis@sgi.com>
    ---
    kernel/workqueue.c | 14 ++++----------
    1 file changed, 4 insertions(+), 10 deletions(-)

    --- linux-2.6-for-ingo.orig/kernel/workqueue.c
    +++ linux-2.6-for-ingo/kernel/workqueue.c
    @@ -991,8 +991,8 @@ static void do_work_for_cpu(struct work_
    * @fn: the function to run
    * @arg: the function arg
    *
    - * This will return -EINVAL in the cpu is not online, or the return value
    - * of @fn otherwise.
    + * This will return the value @fn returns.
    + * It is up to the caller to ensure that the cpu doesn't go offline.
    */
    long work_on_cpu(unsigned int cpu, long (*fn)(void *), void *arg)
    {
    @@ -1001,14 +1001,8 @@ long work_on_cpu(unsigned int cpu, long
    INIT_WORK(&wfc.work, do_work_for_cpu);
    wfc.fn = fn;
    wfc.arg = arg;
    - get_online_cpus();
    - if (unlikely(!cpu_online(cpu)))
    - wfc.ret = -EINVAL;
    - else {
    - schedule_work_on(cpu, &wfc.work);
    - flush_work(&wfc.work);
    - }
    - put_online_cpus();
    + schedule_work_on(cpu, &wfc.work);
    + flush_work(&wfc.work);

    return wfc.ret;
    }
    --


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