linux-kernel - Re: [PATCH] Fix a CFQ crash in "for-2.6.33" branch of block tree

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Message-ID: <x49ljhalmto.fsf@segfault.boston.devel.redhat.com>
Date:	Thu, 10 Dec 2009 13:13:07 -0500
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Jens Axboe <jens.axboe@...cle.com>,
	linux kernel mailing list <linux-kernel@...r.kernel.org>,
	Gui Jianfeng <guijianfeng@...fujitsu.com>
Subject: Re: [PATCH] Fix a CFQ crash in "for-2.6.33" branch of block tree

Vivek Goyal <vgoyal@...hat.com> writes:

> I think I have hit following BUG_ON() in cfq_dispatch_request().
>
> BUG_ON(RB_EMPTY_ROOT(&cfqq->sort_list));
>
> Please find attached the patch to fix it. I have done some stress testing
> with it and have not seen it happening again.
>
>
> o We should wait on a queue even after slice expiry only if it is empty. If
>   queue is not empty then continue to expire it.
>
> o If we decide to keep the queue then make cfqq=NULL. Otherwise select_queue()
>   will return a valid cfqq and cfq_dispatch_request() can hit following
>   BUG_ON().
>
>   BUG_ON(RB_EMPTY_ROOT(&cfqq->sort_list))
>
> Signed-off-by: Vivek Goyal <vgoyal@...hat.com>
Reviewed-by: Jeff Moyer <jmoyer@...hat.com>
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