ext4: Don't claim block from group which has corrupt bitmap

In ext4_mb_complex_scan_group, if the extent length of the newly
found extentet is greater than than the total free blocks counted
in group info, break without claiming the block.

Document different ext4_error usage, explaining the state with which we
continue if we mount with errors=continue

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Mingming Cao <cmm@us.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 15 insertions, 1 deletions

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 2121184a3fa5..6968c53e62ad 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -967,6 +967,10 @@ static void ext4_mb_generate_buddy(struct super_block *sb,
                 ext4_error(sb, __FUNCTION__,
                         "EXT4-fs: group %lu: %u blocks in bitmap, %u in gd\n",
                         group, free, grp->bb_free);
+                /*
+                 * If we intent to continue, we consider group descritor
+                 * corrupt and update bb_free using bitmap value
+                 */
                 grp->bb_free = free;
         }
 
@@ -1822,7 +1826,7 @@ static void ext4_mb_complex_scan_group(struct ext4_allocation_context *ac,
                                                 EXT4_BLOCKS_PER_GROUP(sb), i);
                 if (i >= EXT4_BLOCKS_PER_GROUP(sb)) {
                         /*
-                         * IF we corrupt the bitmap  we won't find any
+                         * IF we have corrupt bitmap, we won't find any
                          * free blocks even though group info says we
                          * we have free blocks
                          */
@@ -1838,6 +1842,12 @@ static void ext4_mb_complex_scan_group(struct ext4_allocation_context *ac,
                         ext4_error(sb, __FUNCTION__, "%d free blocks as per "
                                         "group info. But got %d blocks\n",
                                         free, ex.fe_len);
+                        /*
+                         * The number of free blocks differs. This mostly
+                         * indicate that the bitmap is corrupt. So exit
+                         * without claiming the space.
+                         */
+                        break;
                 }
 
                 ext4_mb_measure_extent(ac, &ex, e4b);
@@ -3771,6 +3781,10 @@ static int ext4_mb_release_inode_pa(struct ext4_buddy *e4b,
                         (unsigned long) pa->pa_len);
                 ext4_error(sb, __FUNCTION__, "free %u, pa_free %u\n",
                                                 free, pa->pa_free);
+                /*
+                 * pa is already deleted so we use the value obtained
+                 * from the bitmap and continue.
+                 */
         }
         atomic_add(free, &sbi->s_mb_discarded);
         if (ac)