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    Subject[tip:sched/core] stop_machine: Introduce __cpu_stop_queue_work() and cpu_stop_queue_two_works()
    Commit-ID:  5caa1c089aebcb83ccd5b79a3b88b0aa58288d05
    Gitweb: http://git.kernel.org/tip/5caa1c089aebcb83ccd5b79a3b88b0aa58288d05
    Author: Oleg Nesterov <oleg@redhat.com>
    AuthorDate: Thu, 8 Oct 2015 16:51:34 +0200
    Committer: Ingo Molnar <mingo@kernel.org>
    CommitDate: Tue, 20 Oct 2015 10:23:54 +0200

    stop_machine: Introduce __cpu_stop_queue_work() and cpu_stop_queue_two_works()

    Preparation to simplify the review of the next change. Add two simple
    helpers, __cpu_stop_queue_work() and cpu_stop_queue_two_works() which
    simply take a bit of code from their callers.

    Signed-off-by: Oleg Nesterov <oleg@redhat.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Mike Galbraith <efault@gmx.de>
    Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Rik van Riel <riel@redhat.com>
    Cc: Tejun Heo <tj@kernel.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: heiko.carstens@de.ibm.com
    Link: http://lkml.kernel.org/r/20151008145134.GA18146@redhat.com
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    ---
    kernel/stop_machine.c | 37 ++++++++++++++++++++++++++-----------
    1 file changed, 26 insertions(+), 11 deletions(-)

    diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
    index 6a40209..688d6b3 100644
    --- a/kernel/stop_machine.c
    +++ b/kernel/stop_machine.c
    @@ -73,21 +73,24 @@ static void cpu_stop_signal_done(struct cpu_stop_done *done, bool executed)
    }
    }

    +static void __cpu_stop_queue_work(struct cpu_stopper *stopper,
    + struct cpu_stop_work *work)
    +{
    + list_add_tail(&work->list, &stopper->works);
    + wake_up_process(stopper->thread);
    +}
    +
    /* queue @work to @stopper. if offline, @work is completed immediately */
    static void cpu_stop_queue_work(unsigned int cpu, struct cpu_stop_work *work)
    {
    struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
    -
    unsigned long flags;

    spin_lock_irqsave(&stopper->lock, flags);
    -
    - if (stopper->enabled) {
    - list_add_tail(&work->list, &stopper->works);
    - wake_up_process(stopper->thread);
    - } else
    + if (stopper->enabled)
    + __cpu_stop_queue_work(stopper, work);
    + else
    cpu_stop_signal_done(work->done, false);
    -
    spin_unlock_irqrestore(&stopper->lock, flags);
    }

    @@ -213,6 +216,16 @@ static int multi_cpu_stop(void *data)
    return err;
    }

    +static int cpu_stop_queue_two_works(int cpu1, struct cpu_stop_work *work1,
    + int cpu2, struct cpu_stop_work *work2)
    +{
    + lg_double_lock(&stop_cpus_lock, cpu1, cpu2);
    + cpu_stop_queue_work(cpu1, work1);
    + cpu_stop_queue_work(cpu2, work2);
    + lg_double_unlock(&stop_cpus_lock, cpu1, cpu2);
    +
    + return 0;
    +}
    /**
    * stop_two_cpus - stops two cpus
    * @cpu1: the cpu to stop
    @@ -260,10 +273,12 @@ int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *
    return -ENOENT;
    }

    - lg_double_lock(&stop_cpus_lock, cpu1, cpu2);
    - cpu_stop_queue_work(cpu1, &work1);
    - cpu_stop_queue_work(cpu2, &work2);
    - lg_double_unlock(&stop_cpus_lock, cpu1, cpu2);
    + if (cpu1 > cpu2)
    + swap(cpu1, cpu2);
    + if (cpu_stop_queue_two_works(cpu1, &work1, cpu2, &work2)) {
    + preempt_enable();
    + return -ENOENT;
    + }

    preempt_enable();


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