dm snapshot: fix metadata corruption
authorMikulas Patocka <mpatocka@redhat.com>
Mon, 3 Mar 2014 22:19:22 +0000 (17:19 -0500)
committerMike Snitzer <snitzer@redhat.com>
Mon, 3 Mar 2014 22:58:13 +0000 (17:58 -0500)
Commit 55494bf2947dccdf2 ("dm snapshot: use dm-bufio") broke snapshots.
Before that 3.14-rc1 commit, loading a snapshot's list of exceptions
involved reading exception areas one by one into ps->area and inserting
those exceptions into the hash table.  Commit 55494bf2947dccdf2 changed
it so that dm-bufio with prefetch is used to load exceptions in batchs.
Exceptions are loaded correctly, but ps->area is left uninitialized.
When a new exception is allocated, it is stored in this uninitialized
ps->area which will be written to the disk.  This causes metadata
corruption.

Fix this corruption by copying the last area that was read via dm-bufio
into ps->area.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
drivers/md/dm-snap-persistent.c

index afc3d01..d6e8817 100644 (file)
@@ -546,6 +546,9 @@ static int read_exceptions(struct pstore *ps,
                r = insert_exceptions(ps, area, callback, callback_context,
                                      &full);
 
+               if (!full)
+                       memcpy(ps->area, area, ps->store->chunk_size << SECTOR_SHIFT);
+
                dm_bufio_release(bp);
 
                dm_bufio_forget(client, chunk);