linux-kernel - Re: [PATCH] fs: Fix mod_timer crash when removing USB sticks

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Message-ID: <CA+5PVA7Yffs3-qdq6pSqDKLLngU7kBsdE92e31NnAM0=wrwp4w@mail.gmail.com>
Date:	Fri, 13 Jan 2012 00:42:07 -0500
From:	Josh Boyer <jwboyer@...il.com>
To:	Paul Taysom <taysom@...omium.org>
Cc:	Paul Taysom <taysom@...gle.com>, Mandeep Baines <msb@...omium.org>,
	Olof Johansson <olofj@...omium.org>, Greg KH <greg@...ah.com>,
	Jens Axboe <axboe@...nel.dk>, Theodore Tso <tytso@...gle.com>,
	Andrew Morton <akpm@...gle.com>, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] fs: Fix mod_timer crash when removing USB sticks

On Thu, Jan 12, 2012 at 4:15 PM, Paul Taysom <taysom@...omium.org> wrote:
> From: Paul Taysom <taysom@...gle.com>
>
> A USB stick with a ext file system on it, would occasionally crash
> when the stick was pulled.
>
> The problem was a timer was being set on the Backing Device Interface,
> bdi, after the USB device had been removed and the bdi had been
> unregistered. The bdi would then be later reinitialized by zeroing
> the timer without removing from the timer from the timer queue.
> This would eventually result in a kernel crash (NULL ptr dereference).

What backtrace did you see when it crashed?  There have been a number of
reports where sd_revalidate_disk is at the top of the backtrace and this sounds
like it might be related.

josh
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