On Wed 10-07-24 12:06:37, libaokun@xxxxxxxxxxxxxxx wrote:
> From: Baokun Li <libaokun1@xxxxxxxxxx>
>
> In ext4_ext_try_to_merge_up(), set path[1].p_bh to NULL after it has been
> released, otherwise it may be released twice.
>
> An example of what triggers this is as follows:
>
> split2 map split1
> |--------|-------|--------|
>
> ext4_ext_map_blocks
> ext4_ext_handle_unwritten_extents
> ext4_split_convert_extents
> // path->p_depth == 0
> ext4_split_extent
> // 1. do split1
> ext4_split_extent_at
> ext4_ext_insert_extent
> ext4_ext_create_new_leaf
> ext4_ext_grow_indepth
> le16_add_cpu(&neh->eh_depth, 1)
> ext4_find_extent
> path->p_depth = 1
> ext4_ext_try_to_merge
> ext4_ext_try_to_merge_up
> path->p_depth = 0
> brelse(path[1].p_bh) ---> not set to NULL here
> // 2. update path
> ext4_find_extent
> // 3. do split2
> ext4_split_extent_at
> ext4_ext_insert_extent
> ext4_ext_create_new_leaf
> ext4_ext_grow_indepth
> le16_add_cpu(&neh->eh_depth, 1)
> ext4_find_extent
> path[0].p_bh = NULL;
> path->p_depth = 1
> read_extent_tree_block ---> return err
> // path[1].p_bh is still the old value
> ext4_free_ext_path
> ext4_ext_drop_refs
> // path->p_depth == 1
> brelse(path[1].p_bh) ---> brelse a buffer twice
>
> Finally got the following WARRNING when removing the buffer from lru:
>
> ============================================
> VFS: brelse: Trying to free free buffer
> WARNING: CPU: 2 PID: 72 at fs/buffer.c:1241 __brelse+0x58/0x90
> CPU: 2 PID: 72 Comm: kworker/u19:1 Not tainted 6.9.0-dirty #716
> RIP: 0010:__brelse+0x58/0x90
> Call Trace:
> <TASK>
> __find_get_block+0x6e7/0x810
> bdev_getblk+0x2b/0x480
> __ext4_get_inode_loc+0x48a/0x1240
> ext4_get_inode_loc+0xb2/0x150
> ext4_reserve_inode_write+0xb7/0x230
> __ext4_mark_inode_dirty+0x144/0x6a0
> ext4_ext_insert_extent+0x9c8/0x3230
> ext4_ext_map_blocks+0xf45/0x2dc0
> ext4_map_blocks+0x724/0x1700
> ext4_do_writepages+0x12d6/0x2a70
> [...]
> ============================================
>
> Fixes: ecb94f5fdf4b ("ext4: collapse a single extent tree block into the inode if possible")
> Cc: stable@xxxxxxxxxx
> Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
Looks good. Feel free to add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Honza
> ---
> fs/ext4/extents.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index 4d589d34b30e..657baf3991c1 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -1888,6 +1888,7 @@ static void ext4_ext_try_to_merge_up(handle_t *handle,
> path[0].p_hdr->eh_max = cpu_to_le16(max_root);
>
> brelse(path[1].p_bh);
> + path[1].p_bh = NULL;
> ext4_free_blocks(handle, inode, NULL, blk, 1,
> EXT4_FREE_BLOCKS_METADATA | EXT4_FREE_BLOCKS_FORGET);
> }
> --
> 2.39.2
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
