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

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Message-ID: <20160225142338.42e46f2c@gandalf.local.home>
Date:	Thu, 25 Feb 2016 14:23:38 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Peter Hurley <peter@...leysoftware.com>,
	Jiri Slaby <jslaby@...e.cz>,
	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 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.

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?

-- Steve