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From: "Paul E. McKenney" <paulmck@kernel.org>
To: Marco Elver <elver@google.com>
Cc: Steven Rostedt <rostedt@goodmis.org>,
	Anders Roxell <anders.roxell@linaro.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Alexander Potapenko <glider@google.com>,
	Dmitry Vyukov <dvyukov@google.com>, Jann Horn <jannh@google.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux-MM <linux-mm@kvack.org>,
	kasan-dev <kasan-dev@googlegroups.com>,
	rcu@vger.kernel.org, peterz@infradead.org
Subject: Re: [PATCH] kfence: Avoid stalling work queue task without allocations
Date: Wed, 11 Nov 2020 16:11:29 -0800
Message-ID: <20201112001129.GD3249@paulmck-ThinkPad-P72> (raw)
In-Reply-To: <20201111202153.GT517454@elver.google.com>

On Wed, Nov 11, 2020 at 09:21:53PM +0100, Marco Elver wrote:
> On Wed, Nov 11, 2020 at 11:21AM -0800, Paul E. McKenney wrote:
> [...]
> > > >     rcu: Don't invoke try_invoke_on_locked_down_task() with irqs disabled
> > > 
> > > Sadly, no, next-20201110 already included that one, and that's what I
> > > tested and got me all those warnings above.
> > 
> > Hey, I had to ask!  The only uncertainty I seee is the acquisition of
> > the lock in rcu_iw_handler(), for which I add a lockdep check in the
> > (untested) patch below.  The other thing I could do is sprinkle such
> > checks through the stall-warning code on the assumption that something
> > RCU is calling is enabling interrupts.
> > 
> > Other thoughts?
> > 
> > 							Thanx, Paul
> > 
> > ------------------------------------------------------------------------
> > 
> > diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
> > index 70d48c5..3d67650 100644
> > --- a/kernel/rcu/tree_stall.h
> > +++ b/kernel/rcu/tree_stall.h
> > @@ -189,6 +189,7 @@ static void rcu_iw_handler(struct irq_work *iwp)
> >  
> >  	rdp = container_of(iwp, struct rcu_data, rcu_iw);
> >  	rnp = rdp->mynode;
> > +	lockdep_assert_irqs_disabled();
> >  	raw_spin_lock_rcu_node(rnp);
> >  	if (!WARN_ON_ONCE(!rdp->rcu_iw_pending)) {
> >  		rdp->rcu_iw_gp_seq = rnp->gp_seq;
> 
> This assert didn't fire yet, I just get more of the below. I'll keep
> rerunning, but am not too hopeful...

Is bisection a possibility?

Failing that, please see the updated patch below.  This adds a few more
calls to lockdep_assert_irqs_disabled(), but perhaps more helpfully dumps
the current stack of the CPU that the RCU grace-period kthread wants to
run on in the case where this kthread has been starved of CPU.

							Thanx, Paul

------------------------------------------------------------------------

diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index 70d48c5..d203ea0 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -189,6 +189,7 @@ static void rcu_iw_handler(struct irq_work *iwp)
 
 	rdp = container_of(iwp, struct rcu_data, rcu_iw);
 	rnp = rdp->mynode;
+	lockdep_assert_irqs_disabled();
 	raw_spin_lock_rcu_node(rnp);
 	if (!WARN_ON_ONCE(!rdp->rcu_iw_pending)) {
 		rdp->rcu_iw_gp_seq = rnp->gp_seq;
@@ -449,21 +450,32 @@ static void print_cpu_stall_info(int cpu)
 /* Complain about starvation of grace-period kthread.  */
 static void rcu_check_gp_kthread_starvation(void)
 {
+	int cpu;
 	struct task_struct *gpk = rcu_state.gp_kthread;
 	unsigned long j;
 
 	if (rcu_is_gp_kthread_starving(&j)) {
+		cpu = gpk ? task_cpu(gpk) : -1;
 		pr_err("%s kthread starved for %ld jiffies! g%ld f%#x %s(%d) ->state=%#lx ->cpu=%d\n",
 		       rcu_state.name, j,
 		       (long)rcu_seq_current(&rcu_state.gp_seq),
 		       data_race(rcu_state.gp_flags),
 		       gp_state_getname(rcu_state.gp_state), rcu_state.gp_state,
-		       gpk ? gpk->state : ~0, gpk ? task_cpu(gpk) : -1);
+		       gpk ? gpk->state : ~0, cpu);
 		if (gpk) {
 			pr_err("\tUnless %s kthread gets sufficient CPU time, OOM is now expected behavior.\n", rcu_state.name);
 			pr_err("RCU grace-period kthread stack dump:\n");
+			lockdep_assert_irqs_disabled();
 			sched_show_task(gpk);
+			lockdep_assert_irqs_disabled();
+			if (cpu >= 0) {
+				pr_err("Stack dump where RCU grace-period kthread last ran:\n");
+				if (!trigger_single_cpu_backtrace(cpu))
+					dump_cpu_task(cpu);
+			}
+			lockdep_assert_irqs_disabled();
 			wake_up_process(gpk);
+			lockdep_assert_irqs_disabled();
 		}
 	}
 }

  reply index

Thread overview: 63+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-10 13:53 Marco Elver
2020-11-10 14:25 ` Dmitry Vyukov
2020-11-10 14:53   ` Marco Elver
2020-11-10 23:23 ` Anders Roxell
2020-11-11  8:29   ` Marco Elver
2020-11-11 13:38     ` Marco Elver
2020-11-11 18:05       ` Steven Rostedt
2020-11-11 18:23         ` Paul E. McKenney
2020-11-11 18:34           ` Marco Elver
2020-11-11 19:21             ` Paul E. McKenney
2020-11-11 20:21               ` Marco Elver
2020-11-12  0:11                 ` Paul E. McKenney [this message]
2020-11-12 12:49                   ` Marco Elver
2020-11-12 16:14                     ` Marco Elver
2020-11-12 17:54                       ` Paul E. McKenney
2020-11-12 18:12                         ` Marco Elver
2020-11-12 20:00                           ` Paul E. McKenney
2020-11-13 11:06                             ` Marco Elver
2020-11-13 17:20                               ` Paul E. McKenney
2020-11-13 17:57                         ` Paul E. McKenney
2020-11-17 10:52                           ` Marco Elver
2020-11-17 18:29                             ` Paul E. McKenney
2020-11-18 22:56                               ` Marco Elver
2020-11-18 23:38                                 ` Paul E. McKenney
2020-11-19 12:53                                   ` Marco Elver
2020-11-19 15:14                                     ` Paul E. McKenney
2020-11-19 17:02                                       ` Marco Elver
2020-11-19 18:48                                         ` Paul E. McKenney
2020-11-19 19:38                                           ` linux-next: stall warnings and deadlock on Arm64 (was: [PATCH] kfence: Avoid stalling...) Marco Elver
2020-11-19 21:35                                             ` Paul E. McKenney
2020-11-19 22:53                                               ` Will Deacon
2020-11-20 10:30                                                 ` Mark Rutland
2020-11-20 14:03                                                   ` Marco Elver
2020-11-23 19:32                                                     ` Mark Rutland
2020-11-24 14:03                                                       ` Marco Elver
2020-11-24 15:01                                                         ` Paul E. McKenney
2020-11-24 19:43                                                           ` Mark Rutland
2020-11-24 20:32                                                             ` Steven Rostedt
2020-11-24 19:30                                                         ` Mark Rutland
2020-11-25  9:45                                                           ` Marco Elver
2020-11-25 10:28                                                             ` Mark Rutland
2020-11-20 14:19                                               ` Marco Elver
2020-11-20 14:39                                                 ` Paul E. McKenney
2020-11-20 15:22                                                   ` Mark Rutland
2020-11-20 17:38                                                     ` Paul E. McKenney
2020-11-20 18:02                                                       ` Mark Rutland
2020-11-20 18:57                                                         ` Paul E. McKenney
2020-11-20 15:26                                                 ` Steven Rostedt
2020-11-20 18:17                                                   ` Marco Elver
2020-11-20 18:57                                                     ` Steven Rostedt
2020-11-20 19:16                                                     ` Steven Rostedt
2020-11-20 19:22                                                       ` Marco Elver
2020-11-20 19:27                                     ` [PATCH] kfence: Avoid stalling work queue task without allocations Steven Rostedt
2020-11-23 15:27                                       ` Marco Elver
2020-11-23 16:28                                         ` Steven Rostedt
2020-11-23 16:36                                           ` Steven Rostedt
2020-11-23 18:53                                             ` Marco Elver
2020-11-23 18:42                                           ` Steven Rostedt
2020-11-24  2:59                                             ` Boqun Feng
2020-11-24  3:44                                               ` Paul E. McKenney
2020-11-11 18:21       ` Paul E. McKenney
2020-11-11 15:01     ` Anders Roxell
2020-11-11 15:22       ` Marco Elver

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