Re: [PATCH 19/20] scsi_dh_alua: update 'access_state' field

[Hannes Reinecke <hare@suse.de>]

On 12/30/2015 02:34 PM, Christoph Hellwig wrote:
> On Tue, Dec 08, 2015 at 08:37:39AM +0100, Hannes Reinecke wrote:
>> Track attached SCSI devices and update the 'access_state' field
>> whenever an ALUA state change has been detected.
>>
>> Signed-off-by: Hannes Reinecke <hare@suse.de>
>> ---
>>   drivers/scsi/device_handler/scsi_dh_alua.c | 29 +++++++++++++++++++++++++++++
>>   1 file changed, 29 insertions(+)
>>
>> diff --git a/drivers/scsi/device_handler/scsi_dh_alua.c b/drivers/scsi/device_handler/scsi_dh_alua.c
>> index 6c6ff0b..d01c86407 100644
>> --- a/drivers/scsi/device_handler/scsi_dh_alua.c
>> +++ b/drivers/scsi/device_handler/scsi_dh_alua.c
>> @@ -24,6 +24,7 @@
>>   #include <linux/module.h>
>>   #include <asm/unaligned.h>
>>   #include <scsi/scsi.h>
>> +#include <scsi/scsi_proto.h>
>>   #include <scsi/scsi_dbg.h>
>>   #include <scsi/scsi_eh.h>
>>   #include <scsi/scsi_dh.h>
>> @@ -76,6 +77,7 @@ static struct workqueue_struct *kaluad_wq;
>>   struct alua_port_group {
>>   	struct kref		kref;
>>   	struct list_head	node;
>> +	struct list_head	dh_list;
>>   	unsigned char		device_id_str[256];
>>   	int			device_id_len;
>>   	int			group_id;
>> @@ -93,6 +95,7 @@ struct alua_port_group {
>>   };
>>
>>   struct alua_dh_data {
>> +	struct list_head	node;
>>   	struct alua_port_group	*pg;
>>   	int			rel_port;
>>   	spinlock_t		pg_lock;
>> @@ -243,6 +246,7 @@ struct alua_port_group *alua_get_pg(struct scsi_device *sdev,
>>   	INIT_DELAYED_WORK(&pg->rtpg_work, alua_rtpg_work);
>>   	INIT_LIST_HEAD(&pg->rtpg_list);
>>   	INIT_LIST_HEAD(&pg->node);
>> +	INIT_LIST_HEAD(&pg->dh_list);
>>   	spin_lock_init(&pg->lock);
>>
>>   	/* Re-check list again to catch concurrent updates */
>> @@ -370,13 +374,26 @@ static int alua_check_vpd(struct scsi_device *sdev, struct alua_dh_data *h,
>>   		old_pg = pg;
>>   		/* port_group has changed. Update to new port group */
>>   		if (h->pg != pg) {
>> +			unsigned long flags;
>> +
>>   			old_pg = h->pg;
>>   			rcu_assign_pointer(h->pg, pg);
>> +			spin_lock_irqsave(&old_pg->lock, flags);
>> +			list_del_rcu(&h->node);
>> +			spin_unlock_irqrestore(&old_pg->lock, flags);
>> +			spin_lock_irqsave(&pg->lock, flags);
>> +			list_add_rcu(&h->node, &pg->dh_list);
>> +			spin_unlock_irqrestore(&pg->lock, flags);
>
> I think it makes more sense to remove it from the old list
> before assining the new h->pg pointer to stay consistant.
>
Hmm. Yes, good point.

> Also the add code is not common with the other half of the outer
> branch, it would be nice to find a way to share the code between
> those two branches.
>
Indeed, it would. But so far I haven't found a nice way for that...

>>   		list_for_each_entry(tmp_pg, &port_group_list, node) {
>> +			struct alua_dh_data *h;
>> +
>>   			if (tmp_pg->group_id != group_id)
>>   				continue;
>>   			if (tmp_pg->device_id_len != pg->device_id_len)
>> @@ -639,6 +658,12 @@ static int alua_rtpg(struct scsi_device *sdev, struct alua_port_group *pg)
>>   				continue;
>>   			tmp_pg->state = desc[0] & 0x0f;
>>   			tmp_pg->pref = desc[0] >> 7;
>> +			rcu_read_lock();
>> +			list_for_each_entry_rcu(h, &tmp_pg->dh_list, node) {
>> +				if (h->sdev)
>> +					h->sdev->access_state = desc[0];
>> +			}
>> +			rcu_read_unlock();
>
> І'd expect h->ѕdev to always be non-NULL.  With a little tweak (see below)
> that should indeed be the case.
>
>> @@ -1086,6 +1112,9 @@ static void alua_bus_detach(struct scsi_device *sdev)
>>   	h->sdev = NULL;
>>   	spin_unlock(&h->pg_lock);
>>   	if (pg) {
>> +		spin_lock(&pg->lock);
>> +		list_del_rcu(&h->node);
>> +		spin_unlock(&pg->lock);
>>   		synchronize_rcu();
>>   		if (pg->rtpg_sdev)
>>   			flush_delayed_work(&pg->rtpg_work);
>
> Here we'd just need to make sure to do the list_del before setting
> h->sdev to NULL.
>
Okay, true. Will do.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@suse.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
--
To unsubscribe from this list: send the line "unsubscribe linux-scsi" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html