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

[Gui Jianfeng <guijianfeng@cn.fujitsu.com>]

Vivek Goyal wrote:
...
> 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@redhat.com>

Hi Vivek,

I saw this oops also. This patch seems good to me, and works fine on my box.