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.rutl...@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
------------------------------------------------------------------------
commit f355d19f94bf4361d641fb3dbb9ece0fbac766f8
Author: Peter Zijlstra <pet...@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/000000000000903d5805ab908...@google.com/
Link:
https://lore.kernel.org/lkml/20200928075729.gc2...@hirez.programming.kicks-ass.net/
Reported-by: syzbot+cb3b69ae80afd6535...@syzkaller.appspotmail.com
Signed-off-by: Peter Zijlstra <pet...@infradead.org>
Signed-off-by: Paul E. McKenney <paul...@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;
}
