[SCSI] Fix hang in starved list processing

Close possible infinite loop with interrupts off when devices are
added back to the starved list.

Fixes: http://bugzilla.kernel.org/show_bug.cgi?id=11898
Reported-by: <alex.shi@intel.com>
Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index f5d3b96890dc6d9dd180eb86bb0f2b737a60e7f1..fa45a1a668676c667dbe2bc1749ad44227061d6b 100644 (file)
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -567,15 +567,18 @@ static inline int scsi_host_is_busy(struct Scsi_Host *shost)
  */
 static void scsi_run_queue(struct request_queue *q)
 {
-       struct scsi_device *starved_head = NULL, *sdev = q->queuedata;
+       struct scsi_device *sdev = q->queuedata;
        struct Scsi_Host *shost = sdev->host;
+       LIST_HEAD(starved_list);
        unsigned long flags;
 
        if (scsi_target(sdev)->single_lun)
                scsi_single_lun_run(sdev);
 
        spin_lock_irqsave(shost->host_lock, flags);
-       while (!list_empty(&shost->starved_list) && !scsi_host_is_busy(shost)) {
+       list_splice_init(&shost->starved_list, &starved_list);
+
+       while (!list_empty(&starved_list)) {
                int flagset;
 
                /*
@@ -588,24 +591,18 @@ static void scsi_run_queue(struct request_queue *q)
                 * scsi_request_fn must get the host_lock before checking
                 * or modifying starved_list or starved_entry.
                 */
-               sdev = list_entry(shost->starved_list.next,
-                                         struct scsi_device, starved_entry);
-               /*
-                * The *queue_ready functions can add a device back onto the
-                * starved list's tail, so we must check for a infinite loop.
-                */
-               if (sdev == starved_head)
+               if (scsi_host_is_busy(shost))
                        break;
-               if (!starved_head)
-                       starved_head = sdev;
 
+               sdev = list_entry(starved_list.next,
+                                 struct scsi_device, starved_entry);
+               list_del_init(&sdev->starved_entry);
                if (scsi_target_is_busy(scsi_target(sdev))) {
                        list_move_tail(&sdev->starved_entry,
                                       &shost->starved_list);
                        continue;
                }
 
-               list_del_init(&sdev->starved_entry);
                spin_unlock(shost->host_lock);
 
                spin_lock(sdev->request_queue->queue_lock);
@@ -621,6 +618,8 @@ static void scsi_run_queue(struct request_queue *q)
 
                spin_lock(shost->host_lock);
        }
+       /* put any unprocessed entries back */
+       list_splice(&starved_list, &shost->starved_list);
        spin_unlock_irqrestore(shost->host_lock, flags);
 
        blk_run_queue(q);