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From: Mark Rutland <mark.rutland@arm.com>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Marco Elver <elver@google.com>,
	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
Subject: Re: linux-next: stall warnings and deadlock on Arm64 (was: [PATCH] kfence: Avoid stalling...)
Date: Fri, 20 Nov 2020 18:02:06 +0000
Message-ID: <20201120180206.GF2328@C02TD0UTHF1T.local> (raw)
In-Reply-To: <20201120173824.GJ1437@paulmck-ThinkPad-P72>

On Fri, Nov 20, 2020 at 09:38:24AM -0800, Paul E. McKenney wrote:
> On Fri, Nov 20, 2020 at 03:22:00PM +0000, Mark Rutland wrote:
> > On Fri, Nov 20, 2020 at 06:39:28AM -0800, Paul E. McKenney wrote:
> > > On Fri, Nov 20, 2020 at 03:19:28PM +0100, Marco Elver wrote:
> > > > I found that disabling ftrace for some of kernel/rcu (see below) solved
> > > > the stalls (and any mention of deadlocks as a side-effect I assume),
> > > > resulting in successful boot.
> > > > 
> > > > Does that provide any additional clues? I tried to narrow it down to 1-2
> > > > files, but that doesn't seem to work.
> > > 
> > > There were similar issues during the x86/entry work.  Are the ARM guys
> > > doing arm64/entry work now?
> > 
> > I'm currently looking at it. I had been trying to shift things to C for
> > a while, and right now I'm trying to fix the lockdep state tracking,
> > which is requiring untangling lockdep/rcu/tracing.
> > 
> > The main issue I see remaining atm is that we don't save/restore the
> > lockdep state over exceptions taken from kernel to kernel. That could
> > result in lockdep thinking IRQs are disabled when they're actually
> > enabled (because code in the nested context might do a save/restore
> > while IRQs are disabled, then return to a context where IRQs are
> > enabled), but AFAICT shouldn't result in the inverse in most cases since
> > the non-NMI handlers all call lockdep_hardirqs_disabled().
> > 
> > I'm at a loss to explaim the rcu vs ftrace bits, so if you have any
> > pointers to the issuies ween with the x86 rework that'd be quite handy.
> 
> There were several over a number of months.  I especially recall issues
> with the direct-from-idle execution of smp_call_function*() handlers,
> and also with some of the special cases in the entry code, for example,
> reentering the kernel from the kernel.  This latter could cause RCU to
> not be watching when it should have been or vice versa.

Ah; those are precisely the cases I'm currently fixing, so if we're
lucky this is an indirect result of one of those rather than a novel
source of pain...

> I would of course be most aware of the issues that impinged on RCU
> and that were located by rcutorture.  This is actually not hard to run,
> especially if the ARM bits in the scripting have managed to avoid bitrot.
> The "modprobe rcutorture" approach has fewer dependencies.  Either way:
> https://paulmck.livejournal.com/57769.html and later posts.

That is a very good idea. I'd been relying on Syzkaller to tickle the
issue, but the torture infrastructure is a much better fit for this
problem. I hadn't realise how comprehensive the scripting was, thanks
for this!

I'll see about giving that a go once I have the irq-from-idle cases
sorted, as those are very obviously broken if you hack
trace_hardirqs_{on,off}() to check that RCU is watching.

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
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 [this message]
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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