ext4: avoid duplicate writes of the backup bg descriptor blocks

The resize code was needlessly writing the backup block group
descriptor blocks multiple times (once per block group) during an
online resize.

Signed-off-by: Yongqiang Yang <xiaoqiangnk@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: stable@vger.kernel.org

1 files changed, 6 insertions, 4 deletions

diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
index a0ee26c23dd8..365d800ff8c1 100644
--- a/fs/ext4/resize.c
+++ b/fs/ext4/resize.c
@@ -1358,13 +1358,15 @@ exit_journal:
                 err = err2;
 
         if (!err) {
-                int i;
+                int gdb_num = group / EXT4_DESC_PER_BLOCK(sb);
+                int gdb_num_end = ((group + flex_gd->count - 1) /
+                                   EXT4_DESC_PER_BLOCK(sb));
+
                 update_backups(sb, sbi->s_sbh->b_blocknr, (char *)es,
                                sizeof(struct ext4_super_block));
-                for (i = 0; i < flex_gd->count; i++, group++) {
+                for (; gdb_num <= gdb_num_end; gdb_num++) {
                         struct buffer_head *gdb_bh;
-                        int gdb_num;
-                        gdb_num = group / EXT4_BLOCKS_PER_GROUP(sb);
+
                         gdb_bh = sbi->s_group_desc[gdb_num];
                         update_backups(sb, gdb_bh->b_blocknr, gdb_bh->b_data,
                                        gdb_bh->b_size);