Re: [PATCH v3 1/8] ext4: only update i_reserved_data_blocks on successful block allocation

Jan Kara
2023-04-12T18:46:49Z

On Wed 12-04-23 20:41:19, Baokun Li wrote:
> In our fault injection test, we create an ext4 file, migrate it to
> non-extent based file, then punch a hole and finally trigger a WARN_ON
> in the ext4_da_update_reserve_space():
>
> EXT4-fs warning (device sda): ext4_da_update_reserve_space:369:
> ino 14, used 11 with only 10 reserved data blocks
>
> When writing back a non-extent based file, if we enable delalloc, the
> number of reserved blocks will be subtracted from the number of blocks
> mapped by ext4_ind_map_blocks(), and the extent status tree will be
> updated. We update the extent status tree by first removing the old
> extent_status and then inserting the new extent_status. If the block range
> we remove happens to be in an extent, then we need to allocate another
> extent_status with ext4_es_alloc_extent().
>
> use old to remove to add new
> |----------|------------|------------|
> old extent_status
>
> The problem is that the allocation of a new extent_status failed due to a
> fault injection, and __es_shrink() did not get free memory, resulting in
> a return of -ENOMEM. Then do_writepages() retries after receiving -ENOMEM,
> we map to the same extent again, and the number of reserved blocks is again
> subtracted from the number of blocks in that extent. Since the blocks in
> the same extent are subtracted twice, we end up triggering WARN_ON at
> ext4_da_update_reserve_space() because used > ei->i_reserved_data_blocks.
>
> For non-extent based file, we update the number of reserved blocks after
> ext4_ind_map_blocks() is executed, which causes a problem that when we call
> ext4_ind_map_blocks() to create a block, it doesn't always create a block,
> but we always reduce the number of reserved blocks. So we move the logic
> for updating reserved blocks to ext4_ind_map_blocks() to ensure that the
> number of reserved blocks is updated only after we do succeed in allocating
> some new blocks.
>
> Fixes: 5f634d064c70 ("ext4: Fix quota accounting error with fallocate")
> Signed-off-by: Baokun Li <libaokun1@huawei.com>

Looks good to me. Feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

Honza

> ---
> V1->V2:
> Modify the patch description and add the Fixes tag.
> V2->V3:
> Remove the redundant judgment of count.
>
> fs/ext4/indirect.c | 8 ++++++++
> fs/ext4/inode.c | 10 ----------
> 2 files changed, 8 insertions(+), 10 deletions(-)
>
> diff --git a/fs/ext4/indirect.c b/fs/ext4/indirect.c
> index c68bebe7ff4b..a9f3716119d3 100644
> --- a/fs/ext4/indirect.c
> +++ b/fs/ext4/indirect.c
> @@ -651,6 +651,14 @@ int ext4_ind_map_blocks(handle_t *handle, struct inode *inode,
>
> ext4_update_inode_fsync_trans(handle, inode, 1);
> count = ar.len;
> +
> + /*
> + * Update reserved blocks/metadata blocks after successful block
> + * allocation which had been deferred till now.
> + */
> + if (flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE)
> + ext4_da_update_reserve_space(inode, count, 1);
> +
> got_it:
> map->m_flags |= EXT4_MAP_MAPPED;
> map->m_pblk = le32_to_cpu(chain[depth-1].key);
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 97eb728cb958..33ae92f0ddfb 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -659,16 +659,6 @@ int ext4_map_blocks(handle_t *handle, struct inode *inode,
> */
> ext4_clear_inode_state(inode, EXT4_STATE_EXT_MIGRATE);
> }
> -
> - /*
> - * Update reserved blocks/metadata blocks after successful
> - * block allocation which had been deferred till now. We don't
> - * support fallocate for non extent files. So we can update
> - * reserve space here.
> - */
> - if ((retval > 0) &&
> - (flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE))
> - ext4_da_update_reserve_space(inode, retval, 1);
> }
>
> if (retval > 0) {
> --
> 2.31.1
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR