From: Mikulas Patocka <mpatocka@redhat.com>
Date: Fri, 16 Oct 2009 22:18:16 +0000 (+0100)
Subject: dm snapshot: lock snapshot while supplying status
X-Git-Tag: v2.6.31.6~77
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=651385e4bbbff823f111e4e8a68b2e1613c34c79;p=karo-tx-linux.git

dm snapshot: lock snapshot while supplying status

commit 4c6fff445d7aa753957856278d4d93bcad6e2c14 upstream.

This patch locks the snapshot when returning status.  It fixes a race
when it could return an invalid number of free chunks if someone
was simultaneously modifying it.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---

diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index 53f4063f7ea4..b9dd22ce47d4 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -1147,6 +1147,8 @@ static int snapshot_status(struct dm_target *ti, status_type_t type,
 	unsigned sz = 0;
 	struct dm_snapshot *snap = ti->private;
 
+	down_write(&snap->lock);
+
 	switch (type) {
 	case STATUSTYPE_INFO:
 		if (!snap->valid)
@@ -1178,6 +1180,8 @@ static int snapshot_status(struct dm_target *ti, status_type_t type,
 		break;
 	}
 
+	up_write(&snap->lock);
+
 	return 0;
 }