linux-kernel - Re: PROBLEM: null pointer dereference in cfq_dispatch

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Message-ID: <20070321190359.GD16768@leiferikson>
Date:	Wed, 21 Mar 2007 20:04:00 +0100
From:	Johannes Weiner <hannes-kernel@...urebad.de>
To:	Dale Blount <linux-kernel@...e.us>
Cc:	linux-kernel@...r.kernel.org, axboe@...nel.dk
Subject: Re: PROBLEM: null pointer dereference in cfq_dispatch_requests (2.6.21-rc2 and 2.6.20)

Hi,

I think I found where the NULL may come from.  Please, anybody, do not
apply this patch before a trustful person reviewed it... Jens? ;)

My thoughts on this are, that there are two possibilities cfqq->next_rq
could be NULL: End of list or a bug when it is set (or not set).
But why does RB_EMPTY_ROOT() as last call in this loop does not trigger?

Did I even get the right place on where the NULL pointer dereference
happens? :)

=Hannes

Signed-off-by: Johannes Weiner <hannes-kernel@...urebad.de>

View attachment "cfq-iosched-NULL-dereference.patch" of type "text/plain" (504 bytes)