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From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
To: Dmitry Vyukov <dvyukov@google.com>,
	paulmck@kernel.org, Petr Mladek <pmladek@suse.com>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: syzbot <syzbot+18379f2a19bc62c12565@syzkaller.appspotmail.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	avagin@gmail.com, Christian Brauner <christian@brauner.io>,
	dbueso@suse.de, LKML <linux-kernel@vger.kernel.org>,
	Oleg Nesterov <oleg@redhat.com>,
	prsood@codeaurora.org,
	syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
	Thomas Gleixner <tglx@linutronix.de>, Tejun Heo <tj@kernel.org>
Subject: Re: INFO: rcu detected stall in sys_exit_group
Date: Fri, 20 Sep 2019 19:22:10 +0900	[thread overview]
Message-ID: <46269171-ff57-8afd-f36b-40e6519b6557@i-love.sakura.ne.jp> (raw)
In-Reply-To: <CACT4Y+YdodVKL2h-Z4Svjyd6kug2ORmfiP4jripSC9PpYw4RiA@mail.gmail.com>

Calling printk() people.

On 2019/09/20 16:50, Dmitry Vyukov wrote:
>>>                                   How it runs on top of an interrupt?
>>
>> It is not running on top of an interrupt.  Its stack was dumped
>> separately.
> 
> I see. Usually the first stack is the traceback of the current stack.
> So I was confused.
> 
>>> And why one cpu tracebacks another one?
>>
>> The usual reason is because neither CPU's quiescent state was reported
>> to the RCU core, so the stall-warning code dumped both stacks.
> 
> But should the other CPU traceback _itself_? Rather than being traced
> back by another CPU?
> E.g. see this report:
> https://github.com/google/syzkaller/blob/master/pkg/report/testdata/linux/report/350#L61-L83
> Here the overall problem was detected by C2, but then C1 traces back itself.
> 
> ... however even in that case C0 and C3 are traced by C2:
> https://github.com/google/syzkaller/blob/master/pkg/report/testdata/linux/report/350#L84-L149
> I can't understand this...
> This makes understanding what happened harder because it's not easy to
> exclude things on other CPUs.

I think this should be
https://github.com/google/syzkaller/blob/master/pkg/report/testdata/linux/report/350#L84-L172
than #L84-L149 .

Is the reason these lines have "[    C2]" is that these lines were flushed (printk_caller_id()
was called) from log_output() from vprintk_store() from vprintk_emit() from vprintk_deferred()
 from printk_deferred() from printk_safe_flush_line() from __printk_safe_flush() from
printk_safe_flush() from printk_safe_flush_on_panic() from panic() ?


  parent reply	other threads:[~2019-09-20 10:22 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-18 11:19 INFO: rcu detected stall in sys_exit_group syzbot
2019-09-18 15:05 ` Dmitry Vyukov
2019-09-19 17:07   ` Paul E. McKenney
2019-09-19 17:39     ` Dmitry Vyukov
2019-09-19 20:12       ` Paul E. McKenney
2019-09-20  7:50         ` Dmitry Vyukov
2019-09-20  7:54           ` Dmitry Vyukov
2019-09-20  8:03             ` Dmitry Vyukov
2019-09-20  8:21               ` Dmitry Vyukov
2019-09-20 13:50                 ` Paul E. McKenney
2019-09-20 10:22           ` Tetsuo Handa [this message]
2019-09-24 14:02             ` Petr Mladek
2019-09-20 13:36           ` Paul E. McKenney

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