dm snapshot: lock snapshot while supplying status
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.
Cc: stable@kernel.org
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index 9cb392b..9bc814a 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -1152,6 +1152,8 @@
unsigned sz = 0;
struct dm_snapshot *snap = ti->private;
+ down_write(&snap->lock);
+
switch (type) {
case STATUSTYPE_INFO:
if (!snap->valid)
@@ -1183,6 +1185,8 @@
break;
}
+ up_write(&snap->lock);
+
return 0;
}