On Sun, 01 Jun 2014 10:08:21 -0400 Sasha Levin <sasha.levin@xxxxxxxxxx> wrote: > On 05/12/2014 12:28 PM, Jan Kara wrote: > > On Wed 07-05-14 22:03:08, Sasha Levin wrote: > >> > Hi all, > >> > > >> > While fuzzing with trinity inside a KVM tools guest running the latest -next > >> > kernel I've stumbled on the following spew: > > Thanks for report. So the problem seems to be maginally valid but I'm not > > 100% sure whom to blame :). So printk() code calls up() which calls > > try_to_wake_up() under console_sem.lock spinlock. That function can take > > rq->lock which is all expected. > > > > The next part of the chain is that during CPU initialization we call > > __sched_fork() with rq->lock which calls into hrtimer_init() which can > > allocate memory which creates a dependency rq->lock => zone.lock.rlock. > > > > And memory management code calls printk() which zone.lock.rlock held which > > closes the loop. Now I suspect the second link in the chain can happen only > > while CPU is booting and might even happen only if some debug options are > > enabled. But I don't really know scheduler code well enough. Steven? > > I've cc'ed Peter and Ingo who may be able to answer that, as it still happens > on -next. > Hmm, it failed on a try lock, but on the spinlock within the trylock. I wonder if we should add this. Peter? -- Steve diff --git a/kernel/locking/semaphore.c b/kernel/locking/semaphore.c index 6815171..6579f84 100644 --- a/kernel/locking/semaphore.c +++ b/kernel/locking/semaphore.c @@ -132,7 +132,9 @@ int down_trylock(struct semaphore *sem) unsigned long flags; int count; - raw_spin_lock_irqsave(&sem->lock, flags); + if (!raw_spin_trylock_irqsave(&sem->lock, flags)) + return 1; + count = sem->count - 1; if (likely(count >= 0)) sem->count = count; -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>