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Re: [Xen-devel] [PATCH] xen-blkfront: fix mq start/stop race

On 07/19/2017 10:08 PM, Konrad Rzeszutek Wilk wrote:
> On Wed, Jul 19, 2017 at 03:51:48PM +0800, Junxiao Bi wrote:
>> Hi Konrad,
>> On 07/19/2017 03:37 PM, Roger Pau Monné wrote:
>>> On Wed, Jul 19, 2017 at 09:19:49AM +0800, Junxiao Bi wrote:
>>>> Hi Roger,
>>>> On 06/23/2017 08:57 PM, Roger Pau Monné wrote:
>>>>> On Thu, Jun 22, 2017 at 09:36:52AM +0800, Junxiao Bi wrote:
>>>>>> When ring buf full, hw queue will be stopped. While blkif interrupt 
>>>>>> consume
>>>>>> request and make free space in ring buf, hw queue will be started again.
>>>>>> But since start queue is protected by spin lock while stop not, that will
>>>>>> cause a race.
>>>>>> interrupt:                                      process:
>>>>>> blkif_interrupt()                               blkif_queue_rq()
>>>>>>  kick_pending_request_queues_locked()
>>>>>>   blk_mq_start_stopped_hw_queues()
>>>>>>    clear_bit(BLK_MQ_S_STOPPED, &hctx->state)
>>>>>> blk_mq_stop_hw_queue(hctx)
>>>>>>    blk_mq_run_hw_queue(hctx, async)
>>>>>> If ring buf is made empty in this case, interrupt will never come, then 
>>>>>> the
>>>>>> hw queue will be stopped forever, all processes waiting for the pending 
>>>>>> io
>>>>>> in the queue will hung.
>>>>>> Signed-off-by: Junxiao Bi <junxiao.bi@xxxxxxxxxx>
>>>>>> Reviewed-by: Ankur Arora <ankur.a.arora@xxxxxxxxxx>
>>>>> Acked-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>>>> Looks patch not in mainline. Can you please help merge it?
>>> I'm afraid this needs to be done by Konrad or one of the Linux
>>> maintainers, I don't have an account on kernel.org in order to send
>>> pull requests to Jens.
>> Can you pls help merge it?
> Could you kindly repost it with the updated tags _and_ against Linus's latest
> branch?
Sure, v2 sent. Please check.

> I get:
> [konrad@char linux]$ git am -s < /tmp/a
> Applying: xen-blkfront: fix mq start/stop race
> error: patch failed: drivers/block/xen-blkfront.c:912
> error: drivers/block/xen-blkfront.c: patch does not apply
> Patch failed at 0001 xen-blkfront: fix mq start/stop race
> The copy of the patch that failed is found in: .git/rebase-apply/patch
> When you have resolved this problem, run "git am --continue".
> If you prefer to skip this patch, run "git am --skip" instead.
> To restore the original branch and stop patching, run "git am --abort".
>> Thanks,
>> Junxiao.
>>> Roger.

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