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

diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
index a0ee26c23dd83375ac74928df688da6903e57c47..365d800ff8c1aaab9929cfdaa56c72401885d4dc 100644 (file)
--- 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);