Re: [PATCH v2 4/8] ext4: avoid bb_free and bb_fragments inconsistency in mb_free_blocks()

On 2024/1/4 18:42, Jan Kara wrote:

On Thu 21-12-23 23:05:54, Baokun Li wrote:

...

After updating bb_free in mb_free_blocks, it is possible to return without updating bb_fragments because the block being freed is found to have already been freed, which leads to inconsistency between bb_free and bb_fragments.

Since the group may be unlocked in ext4_grp_locked_error(), this can lead to problems such as dividing by zero when calculating the average fragment length. Hence move the update of bb_free to after the block double-free check guarantees that the corresponding statistics are updated only after the core block bitmap is modified.

Fixes: eabe0444df90 ("ext4: speed-up releasing blocks on commit") CC: stable@vger.kernel.org # 3.10 Signed-off-by: Baokun Li libaokun1@huawei.com

Just one nit below but regardless of that feel free to add:

Reviewed-by: Jan Kara jack@suse.cz

...

@@ -1941,10 +1936,16 @@ static void mb_free_blocks(struct inode *inode, struct ext4_buddy *e4b, EXT4_GROUP_INFO_BBITMAP_CORRUPT); } else { mb_regenerate_buddy(e4b);

• 	goto check;
  

  }

• goto done;
  

• return;
  

  }

I think this might be more readable when we revert the condition like:

/*
 * Fastcommit replay can free already freed blocks which
 * corrupts allocation info. Regenerate it.
 */
if (sbi->s_mount_state & EXT4_FC_REPLAY) {
              	mb_regenerate_buddy(e4b);
	goto check;
}
             ext4_grp_locked_error(sb, e4b->bd_group,
                                   inode ? inode->i_ino : 0, blocknr,
                                   "freeing already freed block (bit %u); block bitmap corrupt.",
                                   block);
             ext4_mark_group_bitmap_corrupted(sb, e4b->bd_group,
                             EXT4_GROUP_INFO_BBITMAP_CORRUPT);
return;

}

						Honza

Yes, it looks much clearer that way! I will switch to it in the next version.

Thanks a lot!