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stop_machine: Reflow cpu_stop_queue_two_works() 

The code flow in cpu_stop_queue_two_works() is a little arcane; fix this by
lifting the preempt_disable() to the top to create more natural nesting wrt
the spinlocks and make the wake_up_q() and preempt_enable() unconditional
at the end.

Furthermore, enable preemption in the -EDEADLK case, such that we spin-wait
with preemption enabled.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: isaacm@codeaurora.org
Cc: matt@codeblueprint.co.uk
Cc: psodagud@codeaurora.org
Cc: gregkh@linuxfoundation.org
Cc: pkondeti@codeaurora.org
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20180730112140.GH2494@hirez.programming.kicks-ass.net
zero-colors
Peter Zijlstra 2018-07-30 13:21:40 +02:00 committed by Thomas Gleixner
parent b6a60cf36d
commit b80a2bfce8
1 changed files with 23 additions and 18 deletions
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41
kernel/stop_machine.c
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@ -236,13 +236,24 @@ static int cpu_stop_queue_two_works(int cpu1, struct cpu_stop_work *work1,
struct cpu_stopper *stopper2 = per_cpu_ptr(&cpu_stopper, cpu2);
DEFINE_WAKE_Q(wakeq);
int err;
retry:
/*
* The waking up of stopper threads has to happen in the same
* scheduling context as the queueing. Otherwise, there is a
* possibility of one of the above stoppers being woken up by another
* CPU, and preempting us. This will cause us to not wake up the other
* stopper forever.
*/
preempt_disable();
raw_spin_lock_irq(&stopper1->lock);
raw_spin_lock_nested(&stopper2->lock, SINGLE_DEPTH_NESTING);
err = -ENOENT;
if (!stopper1->enabled || !stopper2->enabled)
if (!stopper1->enabled || !stopper2->enabled) {
err = -ENOENT;
goto unlock;
}
/*
* Ensure that if we race with __stop_cpus() the stoppers won't get
* queued up in reverse order leading to system deadlock.
@ -253,36 +264,30 @@ retry:
* It can be falsely true but it is safe to spin until it is cleared,
* queue_stop_cpus_work() does everything under preempt_disable().
*/
err = -EDEADLK;
if (unlikely(stop_cpus_in_progress))
goto unlock;
if (unlikely(stop_cpus_in_progress)) {
err = -EDEADLK;
goto unlock;
}
err = 0;
__cpu_stop_queue_work(stopper1, work1, &wakeq);
__cpu_stop_queue_work(stopper2, work2, &wakeq);
/*
* The waking up of stopper threads has to happen
* in the same scheduling context as the queueing.
* Otherwise, there is a possibility of one of the
* above stoppers being woken up by another CPU,
* and preempting us. This will cause us to n ot
* wake up the other stopper forever.
*/
preempt_disable();
unlock:
raw_spin_unlock(&stopper2->lock);
raw_spin_unlock_irq(&stopper1->lock);
if (unlikely(err == -EDEADLK)) {
preempt_enable();
while (stop_cpus_in_progress)
cpu_relax();
goto retry;
}
if (!err) {
wake_up_q(&wakeq);
preempt_enable();
}
wake_up_q(&wakeq);
preempt_enable();
return err;
}