From 0c06d546a0cff85627e5390e835d806951ee6e09 Mon Sep 17 00:00:00 2001
From: Alex Elder <elder@inktank.com>
Date: Fri, 9 Nov 2012 08:43:15 -0600
Subject: [PATCH] --- yaml --- r: 359580 b: refs/heads/master c:
 a7b4c65f4f15aa657b09d13da8f45ba0b72ec0df h: refs/heads/master v: v3

---
 [refs]                    |  2 +-
 trunk/drivers/block/rbd.c | 36 ++++++++++++++++++++----------------
 2 files changed, 21 insertions(+), 17 deletions(-)

diff --git a/[refs] b/[refs]
index 6895797c1841..dad69d344ef2 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: d78b650a595e23e5a115d332e3c37e019baf7703
+refs/heads/master: a7b4c65f4f15aa657b09d13da8f45ba0b72ec0df
diff --git a/trunk/drivers/block/rbd.c b/trunk/drivers/block/rbd.c
index 2846536d446e..0fbe9add0446 100644
--- a/trunk/drivers/block/rbd.c
+++ b/trunk/drivers/block/rbd.c
@@ -1331,7 +1331,7 @@ static int rbd_do_op(struct request *rq,
 	} else {
 		opcode = CEPH_OSD_OP_READ;
 		flags = CEPH_OSD_FLAG_READ;
-		snapc = NULL;
+		rbd_assert(!snapc);
 		snapid = rbd_dev->spec->snap_id;
 		payload_len = 0;
 	}
@@ -1662,22 +1662,25 @@ static void rbd_rq_fn(struct request_queue *q)
 		}
 		spin_unlock_irq(q->queue_lock);
 
-		/* Stop writes to a read-only device */
-
-		result = -EROFS;
-		if (read_only && rq_data_dir(rq) == WRITE)
-			goto out_end_request;
-
-		/* Grab a reference to the snapshot context */
-
-		down_read(&rbd_dev->header_rwsem);
-		if (atomic_read(&rbd_dev->exists)) {
+		/* Write requests need a reference to the snapshot context */
+
+		if (rq_data_dir(rq) == WRITE) {
+			result = -EROFS;
+			if (read_only) /* Can't write to a read-only device */
+				goto out_end_request;
+
+			/*
+			 * Note that each osd request will take its
+			 * own reference to the snapshot context
+			 * supplied.  The reference we take here
+			 * just guarantees the one we provide stays
+			 * valid.
+			 */
+			down_read(&rbd_dev->header_rwsem);
 			snapc = ceph_get_snap_context(rbd_dev->header.snapc);
+			up_read(&rbd_dev->header_rwsem);
 			rbd_assert(snapc != NULL);
-		}
-		up_read(&rbd_dev->header_rwsem);
-
-		if (!snapc) {
+		} else if (!atomic_read(&rbd_dev->exists)) {
 			rbd_assert(rbd_dev->spec->snap_id != CEPH_NOSNAP);
 			dout("request for non-existent snapshot");
 			result = -ENXIO;
@@ -1689,7 +1692,8 @@ static void rbd_rq_fn(struct request_queue *q)
 				blk_rq_pos(rq) * SECTOR_SIZE,
 				size, rq->bio);
 out_end_request:
-		ceph_put_snap_context(snapc);
+		if (snapc)
+			ceph_put_snap_context(snapc);
 		spin_lock_irq(q->queue_lock);
 		if (!size || result < 0)
 			__blk_end_request_all(rq, result);