On 12/16/20 10:00, Paul E. McKenney wrote: > 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
Oh yeah I remember this one. Yes it could be relevant. I don't see the series in the tree. If it wasn't merged (which AFAICS it isn't), it won't appear there. > I would not expect the patch below to help given what your RCU CPU stall > warning looks like, but just in case... Thanks. If I manage to find a reproducer I will give it a go. Still no luck in triggering it in my test env :( Thanks -- Qais Yousef > > (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; > } >
