Re: [PATCHv2 13/22] scsi_dh_alua: Use workqueue for RTPG

[Hannes Reinecke <hare@suse.de>]

On 01/12/2016 06:14 PM, Christoph Hellwig wrote:
>> -		kref_get(&pg->kref);
>> +		if (!kref_get_unless_zero(&pg->kref))
>> +			continue;
>
> As pointed out earlier this should be done from the start.
>
Yep.

>> +	/* Check for existing port_group references */
>> +	spin_lock(&h->pg_lock);
>> +	if (h->pg) {
>> +		old_pg = pg;
>> +		/* port_group has changed. Update to new port group */
>> +		if (h->pg != pg) {
>> +			old_pg = h->pg;
>> +			rcu_assign_pointer(h->pg, pg);
>> +			pg_updated = true;
>> +		}
>> +	} else {
>> +		rcu_assign_pointer(h->pg, pg);
>> +		pg_updated = true;
>> +	}
>> +	alua_rtpg_queue(h->pg, sdev, NULL);
>> +	spin_unlock(&h->pg_lock);
>> +
>> +	if (pg_updated)
>> +		synchronize_rcu();
>> +	if (old_pg) {
>> +		if (old_pg->rtpg_sdev)
>> +			flush_delayed_work(&old_pg->rtpg_work);
>> +		kref_put(&old_pg->kref, release_port_group);
>> +	}
>
> The synchronize_rcu() needs to be done in release_port_group, or even
> better be replaced by doing a kfree_rcu there instead of a kfree.
>
Point is that we don't necessarily have an old_pg to call 
release_port_group() on, but we still need to call synchronize_rcu()
to inform everyong that h->pg now has a new value.
So while I could do that it would end with a mess of if-clauses here.

> And unless I'm mistaken the flush_delayed_work should probably be
> done in release_port_group as well.
>
_Actually_ we only need to call flush_delayed_work if sdev == 
rtgp_sdev. Otherwise the workqueue item is running off a different 
device and won't be affected.

Cheers,

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