4.18-stable review patch. If anyone has any objections, please let me know.
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From: Peter Zijlstra peterz@infradead.org
commit b80a2bfce85e1051056d98d04ecb2d0b55cbbc1c upstream.
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.... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- kernel/stop_machine.c | 41 +++++++++++++++++++++++------------------ 1 file changed, 23 insertions(+), 18 deletions(-)
--- a/kernel/stop_machine.c +++ b/kernel/stop_machine.c @@ -236,13 +236,24 @@ static int cpu_stop_queue_two_works(int 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; }