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

[Junxiao Bi <junxiao.bi@xxxxxxxxxx>]

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?

Thanks,
Junxiao.
> 
> Thanks, Roger.
> 
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> 


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