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    Subject[tip:sched/core] stop_machine: Don't do for_each_cpu() twice in queue_stop_cpus_work()
    Commit-ID:  b377c2a089d4538e6e62e51fa595c896c314d83d
    Gitweb: http://git.kernel.org/tip/b377c2a089d4538e6e62e51fa595c896c314d83d
    Author: Oleg Nesterov <oleg@redhat.com>
    AuthorDate: Tue, 30 Jun 2015 03:29:48 +0200
    Committer: Ingo Molnar <mingo@kernel.org>
    CommitDate: Mon, 3 Aug 2015 12:21:26 +0200

    stop_machine: Don't do for_each_cpu() twice in queue_stop_cpus_work()

    queue_stop_cpus_work() can do everything in one for_each_cpu() loop.

    Signed-off-by: Oleg Nesterov <oleg@redhat.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Mike Galbraith <efault@gmx.de>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Tejun Heo <tj@kernel.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: dave@stgolabs.net
    Cc: der.herr@hofr.at
    Cc: paulmck@linux.vnet.ibm.com
    Cc: riel@redhat.com
    Cc: viro@ZenIV.linux.org.uk
    Link: http://lkml.kernel.org/r/20150630012948.GA23927@redhat.com
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    ---
    kernel/stop_machine.c | 17 +++++++----------
    1 file changed, 7 insertions(+), 10 deletions(-)

    diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
    index 6e677b0..6212208 100644
    --- a/kernel/stop_machine.c
    +++ b/kernel/stop_machine.c
    @@ -303,22 +303,19 @@ static void queue_stop_cpus_work(const struct cpumask *cpumask,
    struct cpu_stop_work *work;
    unsigned int cpu;

    - /* initialize works and done */
    - for_each_cpu(cpu, cpumask) {
    - work = &per_cpu(cpu_stopper.stop_work, cpu);
    - work->fn = fn;
    - work->arg = arg;
    - work->done = done;
    - }
    -
    /*
    * Disable preemption while queueing to avoid getting
    * preempted by a stopper which might wait for other stoppers
    * to enter @fn which can lead to deadlock.
    */
    lg_global_lock(&stop_cpus_lock);
    - for_each_cpu(cpu, cpumask)
    - cpu_stop_queue_work(cpu, &per_cpu(cpu_stopper.stop_work, cpu));
    + for_each_cpu(cpu, cpumask) {
    + work = &per_cpu(cpu_stopper.stop_work, cpu);
    + work->fn = fn;
    + work->arg = arg;
    + work->done = done;
    + cpu_stop_queue_work(cpu, work);
    + }
    lg_global_unlock(&stop_cpus_lock);
    }


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