[dm-devel] [PATCH 02/13] dm-mpath: Avoid that path removal can trigger an infinite loop

[Hannes Reinecke]

On 04/27/2017 05:11 PM, Bart Van Assche wrote:
> On Thu, 2017-04-27 at 07:46 +0200, Hannes Reinecke wrote:
>> On 04/26/2017 08:37 PM, Bart Van Assche wrote:
>>> +	clone = blk_get_request(q, rq->cmd_flags | REQ_NOMERGE, GFP_ATOMIC);
>>>  	if (IS_ERR(clone)) {
>>>  		/* EBUSY, ENODEV or EWOULDBLOCK: requeue */
>>> -		return r;
>>> +		pr_debug("blk_get_request() returned %ld%s - requeuing\n",
>>> +			 PTR_ERR(clone), blk_queue_dying(q) ?
>>> +			 " (path offline)" : "");
>>> +		if (blk_queue_dying(q)) {
>>> +			atomic_inc(&m->pg_init_in_progress);
>>> +			activate_path(pgpath);
>>> +			return DM_MAPIO_REQUEUE;
>>> +		}
>>> +		return DM_MAPIO_DELAY_REQUEUE;
>>>  	}
>>>  	clone->bio = clone->biotail = NULL;
>>>  	clone->rq_disk = bdev->bd_disk;
>>
>> At the very least this does warrant some inline comments.
>> Why do we call activate_path() here, seeing that the queue is dying?
> 
> Hello Hannes,
> 
> activate_path() is not only able to activate a path but can also change
> the state of a path to offline. The body of the activate_path() function
> makes that clear and that is why I had not added a comment above the
> activate_path() call:
> 
> static void activate_path(struct pgpath *pgpath)
> {
> 	struct request_queue *q = bdev_get_queue(pgpath->path.dev->bdev);
> 
> 	if (pgpath->is_active && !blk_queue_dying(q))
> 		scsi_dh_activate(q, pg_init_done, pgpath);
> 	else
> 		pg_init_done(pgpath, SCSI_DH_DEV_OFFLINED);
> }
> 
So why not call 'pg_init_done()' directly and avoid the confusion?

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
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