1 files changed, 26 insertions, 0 deletions

diff --git a/fs/ubifs/recovery.c b/fs/ubifs/recovery.c
index 936f2cbfe6b6..3dbad6fbd1eb 100644
--- a/fs/ubifs/recovery.c
+++ b/fs/ubifs/recovery.c
@@ -317,6 +317,32 @@ int ubifs_recover_master_node(struct ubifs_info *c)
                         goto out_free;
                 }
                 memcpy(c->rcvrd_mst_node, c->mst_node, UBIFS_MST_NODE_SZ);
+
+                /*
+                 * We had to recover the master node, which means there was an
+                 * unclean reboot. However, it is possible that the master node
+                 * is clean at this point, i.e., %UBIFS_MST_DIRTY is not set.
+                 * E.g., consider the following chain of events:
+                 *
+                 * 1. UBIFS was cleanly unmounted, so the master node is clean
+                 * 2. UBIFS is being mounted R/W and starts changing the master
+                 *    node in the first (%UBIFS_MST_LNUM). A power cut happens,
+                 *    so this LEB ends up with some amount of garbage at the
+                 *    end.
+                 * 3. UBIFS is being mounted R/O. We reach this place and
+                 *    recover the master node from the second LEB
+                 *    (%UBIFS_MST_LNUM + 1). But we cannot update the media
+                 *    because we are being mounted R/O. We have to defer the
+                 *    operation.
+                 * 4. However, this master node (@c->mst_node) is marked as
+                 *    clean (since the step 1). And if we just return, the
+                 *    mount code will be confused and won't recover the master
+                 *    node when it is re-mounter R/W later.
+                 *
+                 *    Thus, to force the recovery by marking the master node as
+                 *    dirty.
+                 */
+                c->mst_node->flags |= cpu_to_le32(UBIFS_MST_DIRTY);
         } else {
                 /* Write the recovered master node */
                 c->max_sqnum = le64_to_cpu(mst->ch.sqnum) - 1;