Re: [PATCH 22/23] scsi_dh_alua: update 'access_state' field

[Ewan Milne <emilne@redhat.com>]

On Mon, 2016-02-08 at 15:34 +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 | 45 ++++++++++++++++++++++++++++--
>  1 file changed, 43 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/scsi/device_handler/scsi_dh_alua.c b/drivers/scsi/device_handler/scsi_dh_alua.c
> index 51126b78..7bcc075 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>
> @@ -75,6 +76,7 @@ struct alua_port_group {
>  	struct kref		kref;
>  	struct rcu_head		rcu;
>  	struct list_head	node;
> +	struct list_head	dh_list;
>  	unsigned char		device_id_str[256];
>  	int			device_id_len;
>  	int			group_id;
> @@ -92,6 +94,7 @@ struct alua_port_group {
>  };
>  
>  struct alua_dh_data {
> +	struct list_head	node;
>  	struct alua_port_group	*pg;
>  	int			group_id;
>  	spinlock_t		pg_lock;
> @@ -247,6 +250,7 @@ struct alua_port_group *alua_alloc_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);
>  
>  	spin_lock(&port_group_lock);
> @@ -328,6 +332,8 @@ static int alua_check_vpd(struct scsi_device *sdev, struct alua_dh_data *h,
>  {
>  	int rel_port = -1, group_id;
>  	struct alua_port_group *pg, *old_pg = NULL;
> +	bool pg_updated;
> +	unsigned long flags;
>  
>  	group_id = scsi_vpd_tpg_id(sdev, &rel_port);
>  	if (group_id < 0) {
> @@ -357,13 +363,25 @@ static int alua_check_vpd(struct scsi_device *sdev, struct alua_dh_data *h,
>  	old_pg = h->pg;
>  	if (old_pg != pg) {
>  		/* port group has changed. Update to new port group */
> +		if (h->pg) {
> +			spin_lock_irqsave(&old_pg->lock, flags);
> +			list_del_rcu(&h->node);
> +			spin_unlock_irqrestore(&old_pg->lock, flags);
> +		}
>  		rcu_assign_pointer(h->pg, pg);
> +		pg_updated = true;
>  	}
>  	if (sdev->synchronous_alua)
>  		pg->flags |= ALUA_SYNC_STPG;
>  	alua_rtpg_queue(h->pg, sdev, NULL, true);
>  	spin_unlock(&h->pg_lock);
>  
> +	if (pg_updated) {
> +		spin_lock_irqsave(&pg->lock, flags);
> +		list_add_rcu(&h->node, &pg->dh_list);
> +		spin_unlock_irqrestore(&pg->lock, flags);
> +	}
> +
>  	if (old_pg)
>  		kref_put(&old_pg->kref, release_port_group);
>  
> @@ -613,8 +631,18 @@ static int alua_rtpg(struct scsi_device *sdev, struct alua_port_group *pg)
>  			if (spin_trylock_irqsave(&tmp_pg->lock, flags)) {
>  				if ((tmp_pg == pg) ||
>  				    !(tmp_pg->flags & ALUA_PG_RUNNING)) {
> +					struct alua_dh_data *h;
> +
>  					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) {
> +						/* h->sdev should always be valid */
> +						BUG_ON(!h->sdev);
> +						h->sdev->access_state = desc[0];

Here you did not mask desc[0] with 0x0f like you did in other places in the code.

> +					}
> +					rcu_read_unlock();
>  				}
>  				if (tmp_pg == pg)
>  					valid_states = desc[1];
> @@ -646,10 +674,19 @@ static int alua_rtpg(struct scsi_device *sdev, struct alua_port_group *pg)
>  			pg->interval = 2;
>  			err = SCSI_DH_RETRY;
>  		} else {
> +			struct alua_dh_data *h;
> +
>  			/* Transitioning time exceeded, set port to standby */
>  			err = SCSI_DH_IO;
>  			pg->state = SCSI_ACCESS_STATE_STANDBY;
>  			pg->expiry = 0;
> +			rcu_read_lock();
> +			list_for_each_entry_rcu(h, &pg->dh_list, node) {
> +				BUG_ON(!h->sdev);
> +				h->sdev->access_state = (pg->state & 0x0f) |
> +					(pg->pref << 7);

Since SCSI_ACCESS_STATE_PREFERRED is #defined as 0x80 in scsi_proto.h you
should use | (pg->pref ? SCSI_ACCESS_STATE_PREFERRED : 0) here rather than
just shifting, otherwise you will have a hard to find bug if somebody
changes the constant.  (But I would prefer keeping them separate anyway.)

> +			}
> +			rcu_read_unlock();
>  		}
>  		break;
>  	case SCSI_ACCESS_STATE_OFFLINE:
> @@ -1053,6 +1090,7 @@ static int alua_bus_attach(struct scsi_device *sdev)
>  	rcu_assign_pointer(h->pg, NULL);
>  	h->init_error = SCSI_DH_OK;
>  	h->sdev = sdev;
> +	INIT_LIST_HEAD(&h->node);
>  
>  	mutex_init(&h->init_mutex);
>  	err = alua_initialize(sdev, h);
> @@ -1082,9 +1120,12 @@ static void alua_bus_detach(struct scsi_device *sdev)
>  	rcu_assign_pointer(h->pg, NULL);
>  	h->sdev = NULL;
>  	spin_unlock(&h->pg_lock);
> -	if (pg)
> +	if (pg) {
> +		spin_lock(&pg->lock);
> +		list_del_rcu(&h->node);
> +		spin_unlock(&pg->lock);
>  		kref_put(&pg->kref, release_port_group);
> -
> +	}
>  	sdev->handler_data = NULL;
>  	kfree(h);
>  }

Reviewed-by: Ewan D. Milne <emilne@redhat.com>