On Wed, Jan 13, 2016 at 08:02:02AM +0100, Hannes Reinecke wrote:
>>> + /* 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.
No, you don't. synchronize_rcu() just waits for all previously
started RCU grace periods to finish. If old_pg doesn't get freed
you don't need to wait for the grace period. synchronize_rcu does
not notify anyone about anything, it just waits.
>> 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.
I'm actually pretty sure I suggested that in an earlier iteratation,
but you said that's not the case. So please only run it if
sdev == rtgp_sdev only then.
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