[SCSI] make blk layer set REQ_SOFTBARRIER on defer and requeue

This is the reworked version of the patch.  It sets REQ_SOFTBARRIER
in two places - in elv_next_request() on BLKPREP_DEFER and in
blk_requeue_request().

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/drivers/block/elevator.c b/drivers/block/elevator.c
index 6b79b4314622..8c51d1ccebbd 100644
--- a/drivers/block/elevator.c
+++ b/drivers/block/elevator.c
@@ -291,6 +291,13 @@ void elv_requeue_request(request_queue_t *q, struct request *rq)
         }
 
         /*
+         * the request is prepped and may have some resources allocated.
+         * allowing unprepped requests to pass this one may cause resource
+         * deadlock.  turn on softbarrier.
+         */
+        rq->flags |= REQ_SOFTBARRIER;
+
+        /*
          * if iosched has an explicit requeue hook, then use that. otherwise
          * just put the request at the front of the queue
          */
@@ -386,6 +393,12 @@ struct request *elv_next_request(request_queue_t *q)
                 if (ret == BLKPREP_OK) {
                         break;
                 } else if (ret == BLKPREP_DEFER) {
+                        /*
+                         * the request may have been (partially) prepped.
+                         * we need to keep this request in the front to
+                         * avoid resource deadlock.  turn on softbarrier.
+                         */
+                        rq->flags |= REQ_SOFTBARRIER;
                         rq = NULL;
                         break;
                 } else if (ret == BLKPREP_KILL) {