ext4: avoid resizing to a partial cluster size

This patch avoids an attempt to resize the filesystem to an
unaligned cluster boundary.  An online resize to a size that is not
integral to cluster size results in the last iteration attempting to
grow the fs by a negative amount, which trips a BUG_ON and leaves the fs
with a corrupted in-memory superblock.

Signed-off-by: Oleg Kiselev <okiselev@amazon.com>
Link: https://lore.kernel.org/r/0E92A0AB-4F16-4F1A-94B7-702CC6504FDE@amazon.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
index 5e3a893e600e5d93dd7387d7b410a7aaa64dd807..fea2a68d067b09e2059d869eddf16cc2e004dee4 100644 (file)
--- a/fs/ext4/resize.c
+++ b/fs/ext4/resize.c
@@ -2011,6 +2011,16 @@ int ext4_resize_fs(struct super_block *sb, ext4_fsblk_t n_blocks_count)
        }
        brelse(bh);
 
+       /*
+        * For bigalloc, trim the requested size to the nearest cluster
+        * boundary to avoid creating an unusable filesystem. We do this
+        * silently, instead of returning an error, to avoid breaking
+        * callers that blindly resize the filesystem to the full size of
+        * the underlying block device.
+        */
+       if (ext4_has_feature_bigalloc(sb))
+               n_blocks_count &= ~((1 << EXT4_CLUSTER_BITS(sb)) - 1);
+
 retry:
        o_blocks_count = ext4_blocks_count(es);