linux-kernel - Re: [peterz-queue:sched/lazy] [sched, x86] 74d850cd4c: WARNING:at_kernel/rcu/rcutorture.c:#rcu_torture_stats

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Message-ID: <20241016154048.sdiJ85Zc@linutronix.de>
Date: Wed, 16 Oct 2024 17:40:48 +0200
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: kernel test robot <oliver.sang@...el.com>
Cc: Peter Zijlstra <peterz@...radead.org>, oe-lkp@...ts.linux.dev,
	lkp@...el.com, linux-kernel@...r.kernel.org, rcu@...r.kernel.org
Subject: Re: [peterz-queue:sched/lazy] [sched, x86]  74d850cd4c:
 WARNING:at_kernel/rcu/rcutorture.c:#rcu_torture_stats_print[rcutorture]

On 2024-10-15 15:47:20 [+0800], kernel test robot wrote:
> Hello,
Hi,

it took me a while to reproduce this because it does not trigger without
the ltp userland and this is not downloaded properly so I had to
workaround it. However…

> [   98.006999][  T543] busted-torture: rtc: 00000000639e821e ver: 6796 tfle: 0 rta: 6796 rtaf: 0 rtf: 6787 rtmbe: 1 rtmbkf: 0/0 rtbe: 0 rtbke: 0 rtbf: 0 rtb: 0 nt: 89 barrier: 0/0:0 read-exits: 64 nocb-toggles: 0:0
> [   98.017386][  T543] busted-torture: !!! 
> [   98.017662][  T543] ------------[ cut here ]------------
> [   98.019330][  T543] WARNING: CPU: 0 PID: 543 at kernel/rcu/rcutorture.c:2258 rcu_torture_stats_print+0x24c/0x610 [rcutorture]
> [   98.021831][  T543] Modules linked in: rcutorture torture
…
> [   98.237025][  T543] ------------[ cut here ]------------
> [   98.238052][  T543] WARNING: CPU: 0 PID: 543 at kernel/rcu/rcutorture.c:2263 rcu_torture_stats_print+0x373/0x610 [rcutorture]
> [   98.240000][  T543] Modules linked in: rcutorture torture
…

It took me a while to figure out that this test is using
rcu_busted_torture_deferred_free() which in turn invokes the callback
before the grace period. Buh.
So it looks like LAZY preempt triggers this more reliably than the
normal preempt version…

Sebastian