Merge branch 'for-3.16-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/libata

Pull libata regression fix from Tejun Heo:
"The last libata/for-3.16-fixes pull contained a regression introduced
by 1871ee134b73 ("libata: support the ata host which implements a
queue depth less than 32") which in turn was a fix for a regression
introduced earlier while changing queue tag order to accomodate hard
drives which perform poorly if tags are not allocated in circular
order (ugh...).

The regression happens only for SAS controllers making use of libata
to serve ATA devices. They don't fill an ata_host field which is used
by the new tag allocation function leading to NULL dereference.

This patch adds a new intermediate field ata_host->n_tags which is
initialized for both SAS and !SAS cases to fix the issue"

* 'for-3.16-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/libata:
libata: introduce ata_host->n_tags to avoid oops on SAS controllers

drivers/ata/libata-core.c

···
 static struct ata_queued_cmd *ata_qc_new(struct ata_port *ap)
 {
 	struct ata_queued_cmd *qc = NULL;
-	unsigned int i, tag, max_queue;
-
-	max_queue = ap->scsi_host->can_queue;
+	unsigned int max_queue = ap->host->n_tags;
+	unsigned int i, tag;
 
 	/* no command while frozen */
 	if (unlikely(ap->pflags & ATA_PFLAG_FROZEN))
···
 {
 	spin_lock_init(&host->lock);
 	mutex_init(&host->eh_mutex);
+	host->n_tags = ATA_MAX_QUEUE - 1;
 	host->dev = dev;
 	host->ops = ops;
 }
···
 {
 	int i, rc;
 
-	/*
-	 * The max queue supported by hardware must not be greater than
-	 * ATA_MAX_QUEUE.
-	 */
-	if (sht->can_queue > ATA_MAX_QUEUE) {
-		dev_err(host->dev, "BUG: the hardware max queue is too large\n");
-		WARN_ON(1);
-		return -EINVAL;
-	}
+	host->n_tags = clamp(sht->can_queue, 1, ATA_MAX_QUEUE - 1);
 
 	/* host must have been started */
 	if (!(host->flags & ATA_HOST_STARTED)) {

include/linux/libata.h

···
 	struct device 		*dev;
 	void __iomem * const	*iomap;
 	unsigned int		n_ports;
+	unsigned int		n_tags;			/* nr of NCQ tags */
 	void			*private_data;
 	struct ata_port_operations *ops;
 	unsigned long		flags;