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Re: [dm-devel] [PATCH 4/7] dm mpath: remove process_queued_ios()



On 02/04/2014 04:24 AM, Junichi Nomura wrote:
> On 02/04/14 05:28, Mike Snitzer wrote:
>> @@ -1216,9 +1185,12 @@ static void pg_init_done(void *data, int errors)
>>  
>>  	if (!m->pg_init_required)
>>  		m->queue_io = 0;
>> -
>> -	m->pg_init_delay_retry = delay_retry;
>> -	queue_work(kmultipathd, &m->process_queued_ios);
>> +	else if (m->current_pg) {
>> +		m->pg_init_delay_retry = delay_retry;
>> +		/* Use a small delay to force the use of workqueue context */
>> +		__pg_init_all_paths(m, 50/HZ);
>> +		goto out;
>> +	}
> 
> I think the patch is still broken.
> 
> When "m->pg_init_required && !m->current_pg",
> it ends up with !pg_ready() and no pg_init running.
> So map_io() will not be called and IO will stall.
> 
> What do you think about my suggestion here:
> https://www.redhat.com/archives/dm-devel/2014-February/msg00013.html
> 
Sigh. pg_init_required again...

> Also it's not yet clear why the second parameter of __pg_init_all_paths()
> is needed. (At least, "50/HZ" is typo or something.)
> 
>> @@ -1591,8 +1563,17 @@ static int multipath_ioctl(struct dm_target *ti, unsigned int cmd,
> ...
>> +		if (m->current_pg && m->pg_init_required)
>> +			__pg_init_all_paths(m, 0);
>> +		spin_unlock_irqrestore(&m->lock, flags);
>> +		dm_table_run_md_queue_async(m->ti->table);
>> +	}
> 
> What happens if "!m->current_pg && m->pg_init_required"?
> 
>From the current logic it means that no valid pg was found, so
calling pg_init would be pointless.
We're calling __choose_pgpath() before that, so if that returns
with current_pg == NULL all paths are down, and calling
pg_init would be pointless.

But I think I see to have pg_init_required handling cleared up;
I'll be doing a patch to unset it at the start of __choose_pgpath(),
this we we can be sure that it'll be set correctly.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare suse de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
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