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From: Mark Rutland <mark.rutland@arm.com>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Marco Elver <elver@google.com>, Will Deacon <will@kernel.org>,
	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>,
	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, boqun.feng@gmail.com,
	tglx@linutronix.de
Subject: Re: linux-next: stall warnings and deadlock on Arm64 (was: [PATCH] kfence: Avoid stalling...)
Date: Tue, 24 Nov 2020 19:43:08 +0000
Message-ID: <20201124194308.GC8957@C02TD0UTHF1T.local> (raw)
In-Reply-To: <20201124150146.GH1437@paulmck-ThinkPad-P72>

On Tue, Nov 24, 2020 at 07:01:46AM -0800, Paul E. McKenney wrote:
> On Tue, Nov 24, 2020 at 03:03:10PM +0100, Marco Elver wrote:
> > [   91.184432] =============================
> > [   91.188301] WARNING: suspicious RCU usage
> > [   91.192316] 5.10.0-rc4-next-20201119-00002-g51c2bf0ac853 #25 Tainted: G        W        
> > [   91.197536] -----------------------------
> > [   91.201431] kernel/trace/trace_preemptirq.c:78 RCU not watching trace_hardirqs_off()!
> > [   91.206546] 
> > [   91.206546] other info that might help us debug this:
> > [   91.206546] 
> > [   91.211790] 
> > [   91.211790] rcu_scheduler_active = 2, debug_locks = 0
> > [   91.216454] RCU used illegally from extended quiescent state!
> > [   91.220890] no locks held by swapper/0/0.
> > [   91.224712] 
> > [   91.224712] stack backtrace:
> > [   91.228794] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G        W         5.10.0-rc4-next-20201119-00002-g51c2bf0ac853 #25
> > [   91.234877] Hardware name: linux,dummy-virt (DT)
> > [   91.239032] Call trace:
> > [   91.242587]  dump_backtrace+0x0/0x240
> > [   91.246500]  show_stack+0x34/0x88
> > [   91.250295]  dump_stack+0x140/0x1bc
> > [   91.254159]  lockdep_rcu_suspicious+0xe4/0xf8
> > [   91.258332]  trace_hardirqs_off+0x214/0x330
> > [   91.262462]  trace_graph_return+0x1ac/0x1d8
> > [   91.266564]  ftrace_return_to_handler+0xa4/0x170
> > [   91.270809]  return_to_handler+0x1c/0x38
> > [   91.274826]  default_idle_call+0x94/0x38c
> > [   91.278869]  do_idle+0x240/0x290
> > [   91.282633]  rest_init+0x1e8/0x2dc
> > [   91.286529]  arch_call_rest_init+0x1c/0x28
> > [   91.290585]  start_kernel+0x638/0x670

> This looks like tracing in the idle loop in a place where RCU is not
> watching.  Historically, this has been addressed by using _rcuidle()
> trace events, but the portion of the idle loop that RCU is watching has
> recently increased.  Last I checked, there were still a few holdouts (that
> would splat like this) in x86, though perhaps those have since been fixed.

Yup! I think this is a latent issue my debug hacks revealed (in addition
to a couple of other issues in the idle path), and still affects x86 and
others. It's only noticeable if you hack trace_hardirqs_{on,off}() to
check rcu_is_watching(), which I had at the tip of my tree.

AFAICT, the issue is that arch_cpu_idle() can be dynamically traced with
ftrace, and hence the tracing code can unexpectedly run without RCU
watching. Since that's dynamic tracing, we can avoid it by marking
arch_cpu_idle() and friends as noinstr.

I'll see about getting this fixed before we upstream the debug hack.

Thanks,
Mark.

  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
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 [this message]
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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