linux-kernel - Re: BUG: unable to handle kernel paging request from pty

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Message-ID: <56D00BFA.6060406@suse.cz>
Date:	Fri, 26 Feb 2016 09:25:30 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	Steven Rostedt <rostedt@...dmis.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Peter Hurley <peter@...leysoftware.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	stable <stable@...r.kernel.org>, lwn@....net
Subject: Re: BUG: unable to handle kernel paging request from pty_write [was:
 Linux 4.4.2]

On 02/25/2016, 08:23 PM, Steven Rostedt wrote:
> On Thu, 25 Feb 2016 11:09:35 -0800
> Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> 
> 
>> Jiri, were you messing around with tracing when this happened? Or
>> maybe shutting down CPU's? There was a RCU locking problem with CPU
>> shutdown, maybe this is one of the symptoms. The fix for that is
>> recent, and not in 4.4.2.
>>
>> Adding Steven Rostedt to the cc. Steven, does that look like a possible case?
> 
> Possible: yes. Likely: no
> 
> The recent fix would require shutting down a CPU at the same time as a
> tracepoint is enabled or disabled. Rather difficult to hit, but easier
> on a virtual machine. If Jiri was not enabling/disabling tracepoints or
> shutting down CPUs, then it would not be the bug.

As this is an automatic build, I very doubt a CPU was offlined or
tracepoints enabled. So I see it even less unlikely this to happen
concurrently.

> But as the comm of the bug is gdb and this running on a virtual
> machine, I think the bug may be elsewhere. Corrupt stack possibly?

Seems so (broken stack frame pointer link), as is indicated in other e-mail.

thanks,
-- 
js
suse labs