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

[Boris Ostrovsky <boris.ostrovsky@oracle.com>]

On 06/23/2017 12:58 AM, Junxiao Bi wrote:
> Hi Boris & Juergen,
> 
> Could you help review this patch? This is a race and will cause the io hung.
> 
> Thanks,
> Junxiao.
> 
> On 06/22/2017 09:36 AM, 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@oracle.com>
>> Reviewed-by: Ankur Arora <ankur.a.arora@oracle.com>


Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

but I think Roger (copied) needs to Ack it.

-boris


>> ---
>>   drivers/block/xen-blkfront.c |    2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
>> index 8bb160cd00e1..4767b82b2cf6 100644
>> --- a/drivers/block/xen-blkfront.c
>> +++ b/drivers/block/xen-blkfront.c
>> @@ -912,8 +912,8 @@ out_err:
>>   	return BLK_MQ_RQ_QUEUE_ERROR;
>>   
>>   out_busy:
>> -	spin_unlock_irqrestore(&rinfo->ring_lock, flags);
>>   	blk_mq_stop_hw_queue(hctx);
>> +	spin_unlock_irqrestore(&rinfo->ring_lock, flags);
>>   	return BLK_MQ_RQ_QUEUE_BUSY;
>>   }
>>   
>>
> 

_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xen.org
https://lists.xen.org/xen-devel