Merge branch 'dcache-cleanup'

[firefly-linux-kernel-4.4.55.git] / fs / ubifs / recovery.c

diff --git a/fs/ubifs/recovery.c b/fs/ubifs/recovery.c
index 936f2cbfe6b672437aec08219ad017f0fc6f3074..3dbad6fbd1eba528661e458ae56e97c03c43b609 100644 (file)
--- 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;