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Message-ID: <20201125094517.GA1359135@elver.google.com>
Date: Wed, 25 Nov 2020 10:45:17 +0100
From: Marco Elver <elver@...gle.com>
To: Mark Rutland <mark.rutland@....com>
Cc: Will Deacon <will@...nel.org>,
"Paul E. McKenney" <paulmck@...nel.org>,
Steven Rostedt <rostedt@...dmis.org>,
Anders Roxell <anders.roxell@...aro.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Alexander Potapenko <glider@...gle.com>,
Dmitry Vyukov <dvyukov@...gle.com>,
Jann Horn <jannh@...gle.com>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Linux-MM <linux-mm@...ck.org>,
kasan-dev <kasan-dev@...glegroups.com>, rcu@...r.kernel.org,
Peter Zijlstra <peterz@...radead.org>,
Tejun Heo <tj@...nel.org>,
Lai Jiangshan <jiangshanlai@...il.com>,
linux-arm-kernel@...ts.infradead.org, boqun.feng@...il.com,
tglx@...utronix.de
Subject: Re: linux-next: stall warnings and deadlock on Arm64 (was: [PATCH]
kfence: Avoid stalling...)
On Tue, Nov 24, 2020 at 07:30PM +0000, Mark Rutland wrote:
[...]
> > > I've just updated that branch with a new version which I hope covers
> > > kernel<->kernel transitions too. If you get a chance, would you mind
> > > giving that a spin?
> > >
> > > The HEAD commit should be:
> > >
> > > a51334f033f8ee88 ("HACK: check IRQ tracing has RCU watching")
> >
> > Thank you! Your series appears to work and fixes the stalls and
> > deadlocks (3 trials)!
>
> Thanks for testing! I'm glad that appears to work, as it suggests
> there's not another massive problem lurking in this area.
>
> While cleaning/splitting that up today, I spotted a couple of new
> problems I introduced, and I'm part-way through sorting that out, but
> it's not quite ready today after all. :/
>
> Fingers crossed for tomorrow...
>
> > I noticed there are a bunch of warnings in the log
> > that might be relevant (see attached).
>
> > [ 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
>
> Hmm... I suspect that arch_cpu_idle() is being traced here, and I reckon
> we have to mark that and its callees as noinstr, since it doesn't seem
> sane to have ftrace check whether RCU is watching for every function
> call. Maybe Paul or Steve can correct me. ;)
Yes, it's arch_cpu_idle().
> If you still have the binary lying around, can you check whether
> default_idle_call+0x94/0x38c is just after the call to arch_cpu_idle()?
> If you could dump the asm around that, along with whatever faddr2line
> tells you, that'd be a great help.
I reran to be sure, with similar results. I've attached a
syz-symbolize'd version of the warnings.
Thanks,
-- Marco
View attachment "dmesg-symbolized" of type "text/plain" (19738 bytes)
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