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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, Peter Zijlstra <peterz@infradead.org>,
	Tejun Heo <tj@kernel.org>, Lai Jiangshan <jiangshanlai@gmail.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: linux-next: stall warnings and deadlock on Arm64 (was: [PATCH] kfence: Avoid stalling...)
Date: Thu, 19 Nov 2020 13:35:12 -0800
Message-ID: <20201119213512.GB1437@paulmck-ThinkPad-P72> (raw)
In-Reply-To: <20201119193819.GA2601289@elver.google.com>

On Thu, Nov 19, 2020 at 08:38:19PM +0100, Marco Elver wrote:
> On Thu, Nov 19, 2020 at 10:48AM -0800, Paul E. McKenney wrote:
> > On Thu, Nov 19, 2020 at 06:02:59PM +0100, Marco Elver wrote:

[ . . . ]

> > > I can try bisection again, or reverting some commits that might be
> > > suspicious? But we'd need some selection of suspicious commits.
> > 
> > The report claims that one of the rcu_node ->lock fields is held
> > with interrupts enabled, which would indeed be bad.  Except that all
> > of the stack traces that it shows have these locks held within the
> > scheduling-clock interrupt handler.  Now with the "rcu: Don't invoke
> > try_invoke_on_locked_down_task() with irqs disabled" but without the
> > "sched/core: Allow try_invoke_on_locked_down_task() with irqs disabled"
> > commit, I understand why.  With both, I don't see how this happens.
> 
> I'm at a loss, but happy to keep bisecting and trying patches. I'm also
> considering:
> 
> 	Is it the compiler? Probably not, I tried 2 versions of GCC.
> 
> 	Can we trust lockdep to precisely know IRQ state? I know there's
> 	been some recent work around this, but hopefully we're not
> 	affected here?
> 
> 	Is QEMU buggy?
> 
> > At this point, I am reduced to adding lockdep_assert_irqs_disabled()
> > calls at various points in that code, as shown in the patch below.
> > 
> > At this point, I would guess that your first priority would be the
> > initial bug rather than this following issue, but you never know, this
> > might well help diagnose the initial bug.
> 
> I don't mind either way. I'm worried deadlocking the whole system might
> be worse.

Here is another set of lockdep_assert_irqs_disabled() calls on the
off-chance that they actually find something.

							Thanx, Paul

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

commit bcca5277df3f24db15e15ccc8b05ecf346d05169
Author: Paul E. McKenney <paulmck@kernel.org>
Date:   Thu Nov 19 13:30:33 2020 -0800

    rcu: Add lockdep_assert_irqs_disabled() to raw_spin_unlock_rcu_node() macros
    
    This commit adds a lockdep_assert_irqs_disabled() call to the
    helper macros that release the rcu_node structure's ->lock, namely
    to raw_spin_unlock_rcu_node(), raw_spin_unlock_irq_rcu_node() and
    raw_spin_unlock_irqrestore_rcu_node().  The point of this is to help track
    down a situation where lockdep appears to be insisting that interrupts
    are enabled while holding an rcu_node structure's ->lock.
    
    Link: https://lore.kernel.org/lkml/20201111133813.GA81547@elver.google.com/
    Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 59ef1ae..bf0827d 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -378,7 +378,11 @@ do {									\
 	smp_mb__after_unlock_lock();					\
 } while (0)
 
-#define raw_spin_unlock_rcu_node(p) raw_spin_unlock(&ACCESS_PRIVATE(p, lock))
+#define raw_spin_unlock_rcu_node(p)					\
+do {									\
+	lockdep_assert_irqs_disabled();					\
+	raw_spin_unlock(&ACCESS_PRIVATE(p, lock));			\
+} while (0)
 
 #define raw_spin_lock_irq_rcu_node(p)					\
 do {									\
@@ -387,7 +391,10 @@ do {									\
 } while (0)
 
 #define raw_spin_unlock_irq_rcu_node(p)					\
-	raw_spin_unlock_irq(&ACCESS_PRIVATE(p, lock))
+do {									\
+	lockdep_assert_irqs_disabled();					\
+	raw_spin_unlock_irq(&ACCESS_PRIVATE(p, lock));			\
+} while (0)
 
 #define raw_spin_lock_irqsave_rcu_node(p, flags)			\
 do {									\
@@ -396,7 +403,10 @@ do {									\
 } while (0)
 
 #define raw_spin_unlock_irqrestore_rcu_node(p, flags)			\
-	raw_spin_unlock_irqrestore(&ACCESS_PRIVATE(p, lock), flags)
+do {									\
+	lockdep_assert_irqs_disabled();					\
+	raw_spin_unlock_irqrestore(&ACCESS_PRIVATE(p, lock), flags);	\
+} while (0)
 
 #define raw_spin_trylock_rcu_node(p)					\
 ({									\

  reply index

Thread overview: 63+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-10 13:53 [PATCH] kfence: Avoid stalling work queue task without allocations 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
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 [this message]
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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