linux-kernel - Re: [PATCH 3/8] cfq-iosched: fix oom cfq_queue ref leak in cfq_set

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Message-ID: <x49mw0ahw3o.fsf@segfault.boston.devel.redhat.com>
Date:	Mon, 08 Jun 2015 14:51:39 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	axboe@...nel.dk, linux-kernel@...r.kernel.org,
	cgroups@...r.kernel.org, vgoyal@...hat.com,
	avanzini.arianna@...il.com
Subject: Re: [PATCH 3/8] cfq-iosched: fix oom cfq_queue ref leak in cfq_set_request()

Tejun Heo <tj@...nel.org> writes:

> If the cfq_queue cached in cfq_io_cq is the oom one, cfq_set_request()
> replaces it by invoking cfq_get_queue() again without putting the oom
> queue leaking the reference it was holding.  While oom queues are not
> released through reference counting, they're still reference counted
> and this can theoretically lead to the reference count overflowing and
> incorrectly invoke the usual release path on it.
>
> Fix it by making cfq_set_request() put the ref it was holding.
>
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Cc: Vivek Goyal <vgoyal@...hat.com>
> Cc: Arianna Avanzini <avanzini.arianna@...il.com>

Reviewed-by: Jeff Moyer <jmoyer@...hat.com>
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