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

[Christoph Hellwig <hch@lst.de>]

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.

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.

>  		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.
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