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

2 files changed, 5 insertions, 12 deletions

diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index d19c37a7abc9..677c0c1b03bd 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -4798,9 +4798,8 @@ void swap_buf_le16(u16 *buf, unsigned int buf_words)
 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))
@@ -6094,6 +6093,7 @@ void ata_host_init(struct ata_host *host, struct device *dev,
 {
         spin_lock_init(&host->lock);
         mutex_init(&host->eh_mutex);
+        host->n_tags = ATA_MAX_QUEUE - 1;
         host->dev = dev;
         host->ops = ops;
 }
@@ -6175,15 +6175,7 @@ int ata_host_register(struct ata_host *host, struct scsi_host_template *sht)
 {
         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)) {
diff --git a/include/linux/libata.h b/include/linux/libata.h
index 5ab4e3a76721..92abb497ab14 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -593,6 +593,7 @@ struct ata_host {
         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;