Messages in this thread Patch in this message | | | Date | Wed, 16 Dec 2020 10:00:47 -0800 | From | "Paul E. McKenney" <> | Subject | Re: RCU stall leading to deadlock warning |
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On Wed, Dec 16, 2020 at 09:54:42AM -0800, Paul E. McKenney wrote: > On Wed, Dec 16, 2020 at 05:29:39PM +0000, Qais Yousef wrote: > > Hi Paul > > > > We hit the below splat a couple of days ago in our testing. Sadly I can't > > reproduce it. And it was on android-mainline branch.. > > > > It's the deadlock message that bothers me. I can't see how we could have ended > > there. We detect a stall and when trying to dump the stack LOCKDEP spits the > > warning. > > > > Maybe should take this report with a pinch of salt since it wasn't on mainline. > > I just thought it might be something worth sharing in case you can actually > > spot something obvious that I can't see. If I got more info or a reproducer > > I will share them. > > > > The failure was triggered twice on that day running 2 different tests. > > This looks like the same problem that Mark Rutland's recent patch series > was fixing. Do you have this series applied? > > lore.kernel.org/lkml/20201126123602.23454-1-mark.rutland@arm.com
I would not expect the patch below to help given what your RCU CPU stall warning looks like, but just in case...
(Full disclosure: Peter fixed a bug of mine, filenames notwithstanding.)
Thanx, Paul
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commit f355d19f94bf4361d641fb3dbb9ece0fbac766f8 Author: Peter Zijlstra <peterz@infradead.org> Date: Sat Aug 29 10:22:24 2020 -0700
sched/core: Allow try_invoke_on_locked_down_task() with irqs disabled The try_invoke_on_locked_down_task() function currently requires that interrupts be enabled, but it is called with interrupts disabled from rcu_print_task_stall(), resulting in an "IRQs not enabled as expected" diagnostic. This commit therefore updates try_invoke_on_locked_down_task() to use raw_spin_lock_irqsave() instead of raw_spin_lock_irq(), thus allowing use from either context. Link: https://lore.kernel.org/lkml/000000000000903d5805ab908fc4@google.com/ Link: https://lore.kernel.org/lkml/20200928075729.GC2611@hirez.programming.kicks-ass.net/ Reported-by: syzbot+cb3b69ae80afd6535b0e@syzkaller.appspotmail.com Signed-off-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index b2d6898..4abf041 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2989,7 +2989,7 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) /** * try_invoke_on_locked_down_task - Invoke a function on task in fixed state - * @p: Process for which the function is to be invoked. + * @p: Process for which the function is to be invoked, can be @current. * @func: Function to invoke. * @arg: Argument to function. * @@ -3007,12 +3007,11 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) */ bool try_invoke_on_locked_down_task(struct task_struct *p, bool (*func)(struct task_struct *t, void *arg), void *arg) { - bool ret = false; struct rq_flags rf; + bool ret = false; struct rq *rq; - lockdep_assert_irqs_enabled(); - raw_spin_lock_irq(&p->pi_lock); + raw_spin_lock_irqsave(&p->pi_lock, rf.flags); if (p->on_rq) { rq = __task_rq_lock(p, &rf); if (task_rq(p) == rq) @@ -3029,7 +3028,7 @@ bool try_invoke_on_locked_down_task(struct task_struct *p, bool (*func)(struct t ret = func(p, arg); } } - raw_spin_unlock_irq(&p->pi_lock); + raw_spin_unlock_irqrestore(&p->pi_lock, rf.flags); return ret; }
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