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From: "Paul E. McKenney" <paulmck@kernel.org>
To: Qais Yousef <qais.yousef@arm.com>
Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org,
	kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.com,
	akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
	josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
	rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
	fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org,
	Yanfei Xu <yanfei.xu@windriver.com>
Subject: Re: [PATCH rcu 02/18] rcu: Fix stall-warning deadlock due to non-release of rcu_node ->lock
Date: Wed, 4 Aug 2021 15:33:58 -0700	[thread overview]
Message-ID: <20210804223358.GZ4397@paulmck-ThinkPad-P17-Gen-1> (raw)
In-Reply-To: <20210804135017.g6tfaubvygki2osk@e107158-lin.cambridge.arm.com>

On Wed, Aug 04, 2021 at 02:50:17PM +0100, Qais Yousef wrote:
> On 08/03/21 09:28, Paul E. McKenney wrote:
> > On Tue, Aug 03, 2021 at 05:12:21PM +0100, Qais Yousef wrote:
> > > On 08/03/21 08:52, Paul E. McKenney wrote:
> > > > On Tue, Aug 03, 2021 at 03:24:58PM +0100, Qais Yousef wrote:
> > > > > Hi
> > > > > 
> > > > > On 07/21/21 13:21, Paul E. McKenney wrote:
> > > > > > From: Yanfei Xu <yanfei.xu@windriver.com>
> > > > > > 
> > > > > > If rcu_print_task_stall() is invoked on an rcu_node structure that does
> > > > > > not contain any tasks blocking the current grace period, it takes an
> > > > > > early exit that fails to release that rcu_node structure's lock.  This
> > > > > > results in a self-deadlock, which is detected by lockdep.
> > > > > > 
> > > > > > To reproduce this bug:
> > > > > > 
> > > > > > tools/testing/selftests/rcutorture/bin/kvm.sh --allcpus --duration 3 --trust-make --configs "TREE03" --kconfig "CONFIG_PROVE_LOCKING=y" --bootargs "rcutorture.stall_cpu=30 rcutorture.stall_cpu_block=1 rcutorture.fwd_progress=0 rcutorture.test_boost=0"
> > > > > > 
> > > > > > This will also result in other complaints, including RCU's scheduler
> > > > > > hook complaining about blocking rather than preemption and an rcutorture
> > > > > > writer stall.
> > > > > > 
> > > > > > Only a partial RCU CPU stall warning message will be printed because of
> > > > > > the self-deadlock.
> > > > > > 
> > > > > > This commit therefore releases the lock on the rcu_print_task_stall()
> > > > > > function's early exit path.
> > > > > > 
> > > > > > Fixes: c583bcb8f5ed ("rcu: Don't invoke try_invoke_on_locked_down_task() with irqs disabled")
> > > > > > Signed-off-by: Yanfei Xu <yanfei.xu@windriver.com>
> > > > > > Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> > > > > > ---
> > > > > 
> > > > > We are seeing similar stall/deadlock issue on android 5.10 kernel, is the fix
> > > > > relevant here? Trying to apply the patches and test, but the problem is tricky
> > > > > to reproduce so thought worth asking first.
> > > > 
> > > > Looks like the relevant symptoms to me, so I suggest trying this series
> > > > from -rcu:
> > > > 
> > > > 8baded711edc ("rcu: Fix to include first blocked task in stall warning")
> > > > f6b3995a8b56 ("rcu: Fix stall-warning deadlock due to non-release of rcu_node ->lock")
> > > 
> > > Great thanks. These are the ones we picked as the rest was a bit tricky to
> > > apply on 5.10.
> > > 
> > > While at it, we see these errors too though they look harmless. They happen
> > > all the time
> > > 
> > > 	[  595.292685] NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #02!!!"}
> > > 	[  595.301467] NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #08!!!"}
> > > 	[  595.389353] NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #08!!!"}
> > > 	[  595.397454] NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #08!!!"}
> > > 	[  595.417112] NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #08!!!"}
> > > 	[  595.425215] NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #08!!!"}
> > > 	[  595.438807] NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #08!!!"}
> > > 
> > > I used to see them on mainline a while back but seem to have been fixed.
> > > Something didn't get backported to 5.10 perhaps?
> > 
> > I believe that you need at least this one:
> > 
> > 47c218dcae65 ("tick/sched: Prevent false positive softirq pending warnings on RT")
> 
> After looking at the content of the patch, it's not related. We don't run with
> PREEMPT_RT.
> 
> I think we're hitting a genuine issue, most likely due to out-of-tree changes
> done by Android to fix RT latency problems against softirq (surprise surprise).
> 
> Thanks for your help and sorry for the noise.

No problem!

But I used to see this very frequently in non-PREEMPT_RT rcutorture runs,
and there was a patch from Thomas that made them go away.  So it might
be worth looking at has patches in this area since 5.10.  Maybe I just
got confused and picked the wrong one.

							Thanx, Paul

  reply	other threads:[~2021-08-04 22:34 UTC|newest]

Thread overview: 66+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-21 20:20 [PATCH rcu 0/18] Miscellaneous fixes for v5.15 Paul E. McKenney
2021-07-21 20:21 ` [PATCH rcu 01/18] rcu: Fix to include first blocked task in stall warning Paul E. McKenney
2021-07-21 20:21 ` [PATCH rcu 02/18] rcu: Fix stall-warning deadlock due to non-release of rcu_node ->lock Paul E. McKenney
2021-08-03 14:24   ` Qais Yousef
2021-08-03 15:52     ` Paul E. McKenney
2021-08-03 16:12       ` Qais Yousef
2021-08-03 16:28         ` Paul E. McKenney
2021-08-03 16:33           ` Qais Yousef
2021-08-04 13:50           ` Qais Yousef
2021-08-04 22:33             ` Paul E. McKenney [this message]
2021-08-06  9:56               ` Qais Yousef
2021-08-06  9:57   ` Qais Yousef
2021-08-06 11:43     ` Paul E. McKenney
2021-08-06 12:33       ` Qais Yousef
2021-07-21 20:21 ` [PATCH rcu 03/18] rcu: Remove special bit at the bottom of the ->dynticks counter Paul E. McKenney
2021-07-21 20:21 ` [PATCH rcu 04/18] rcu: Weaken ->dynticks accesses and updates Paul E. McKenney
2021-07-21 20:41   ` Linus Torvalds
2021-07-21 21:25     ` Paul E. McKenney
2021-07-28 17:37   ` [PATCH v2 " Paul E. McKenney
2021-07-28 17:58     ` Linus Torvalds
2021-07-28 18:12       ` Mathieu Desnoyers
2021-07-28 18:32         ` Linus Torvalds
2021-07-28 18:39           ` Mathieu Desnoyers
2021-07-28 18:46         ` Paul E. McKenney
2021-07-28 18:46       ` Paul E. McKenney
2021-07-28 18:57         ` Linus Torvalds
2021-07-28 18:23     ` Mathieu Desnoyers
2021-07-28 18:58       ` Paul E. McKenney
2021-07-28 19:45         ` Paul E. McKenney
2021-07-28 20:03           ` Mathieu Desnoyers
2021-07-28 20:28             ` Paul E. McKenney
2021-07-29 14:41               ` Mathieu Desnoyers
2021-07-29 15:57                 ` Paul E. McKenney
2021-07-29 17:41                   ` Mathieu Desnoyers
2021-07-29 18:05                     ` Paul E. McKenney
2021-07-29 18:42                       ` Mathieu Desnoyers
2021-07-28 20:37     ` Josh Triplett
2021-07-28 20:47       ` Paul E. McKenney
2021-07-28 22:23         ` Frederic Weisbecker
2021-07-29  1:07           ` Paul E. McKenney
2021-07-29  7:58   ` [PATCH " Boqun Feng
2021-07-29 10:53     ` Frederic Weisbecker
2021-07-30  5:56       ` Boqun Feng
2021-07-30 17:18         ` Paul E. McKenney
2021-07-21 20:21 ` [PATCH rcu 05/18] rcu: Mark accesses to ->rcu_read_lock_nesting Paul E. McKenney
2021-07-21 20:21 ` [PATCH rcu 06/18] rculist: Unify documentation about missing list_empty_rcu() Paul E. McKenney
2021-07-21 20:21 ` [PATCH rcu 07/18] rcu/tree: Handle VM stoppage in stall detection Paul E. McKenney
2021-07-21 20:21 ` [PATCH rcu 08/18] rcu: Do not disable GP stall detection in rcu_cpu_stall_reset() Paul E. McKenney
2021-07-21 20:21 ` [PATCH rcu 09/18] rcu: Start timing stall repetitions after warning complete Paul E. McKenney
2021-07-21 20:21 ` [PATCH rcu 10/18] srcutiny: Mark read-side data races Paul E. McKenney
2021-07-29  8:23   ` Boqun Feng
2021-07-29 13:36     ` Paul E. McKenney
2021-07-21 20:21 ` [PATCH rcu 11/18] rcu: Mark lockless ->qsmask read in rcu_check_boost_fail() Paul E. McKenney
2021-07-29  8:54   ` Boqun Feng
2021-07-29 14:03     ` Paul E. McKenney
2021-07-30  2:28       ` Boqun Feng
2021-07-30  3:26         ` Paul E. McKenney
2021-07-21 20:21 ` [PATCH rcu 12/18] rcu: Make rcu_gp_init() and rcu_gp_fqs_loop noinline to conserve stack Paul E. McKenney
2021-07-21 20:21 ` [PATCH rcu 13/18] rcu: Remove trailing spaces and tabs Paul E. McKenney
2021-07-21 20:21 ` [PATCH rcu 14/18] rcu: Mark accesses in tree_stall.h Paul E. McKenney
2021-07-21 20:21 ` [PATCH rcu 15/18] rcu: Remove useless "ret" update in rcu_gp_fqs_loop() Paul E. McKenney
2021-08-03 16:48   ` Joe Perches
2021-08-03 17:10     ` Paul E. McKenney
2021-07-21 20:21 ` [PATCH rcu 16/18] rcu: Use per_cpu_ptr to get the pointer of per_cpu variable Paul E. McKenney
2021-07-21 20:21 ` [PATCH rcu 17/18] rcu: Explain why rcu_all_qs() is a stub in preemptible TREE RCU Paul E. McKenney
2021-07-21 20:21 ` [PATCH rcu 18/18] rcu: Print human-readable message for schedule() in RCU reader Paul E. McKenney

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