Re: [PATCH 1/5] ext4: Fix reusing stale buffer heads from last failed mounting

[Jan Kara <jack@suse.cz>]

On Fri 10-03-23 20:52:02, Zhihao Cheng wrote:
> Following process makes ext4 load stale buffer heads from last failed
> mounting in a new mounting operation:
> mount_bdev
>  ext4_fill_super
>  | ext4_load_and_init_journal
>  |  ext4_load_journal
>  |   jbd2_journal_load
>  |    load_superblock
>  |     journal_get_superblock
>  |      set_buffer_verified(bh) // buffer head is verified
>  |   jbd2_journal_recover // failed caused by EIO
>  | goto failed_mount3a // skip 'sb->s_root' initialization
>  deactivate_locked_super
>   kill_block_super
>    generic_shutdown_super
>     if (sb->s_root)
>     // false, skip ext4_put_super->invalidate_bdev->
>     // invalidate_mapping_pages->mapping_evict_folio->
>     // filemap_release_folio->try_to_free_buffers, which
>     // cannot drop buffer head.
>    blkdev_put
>     blkdev_put_whole
>      if (atomic_dec_and_test(&bdev->bd_openers))
>      // false, systemd-udev happens to open the device. Then
>      // blkdev_flush_mapping->kill_bdev->truncate_inode_pages->
>      // truncate_inode_folio->truncate_cleanup_folio->
>      // folio_invalidate->block_invalidate_folio->
>      // filemap_release_folio->try_to_free_buffers will be skipped,
>      // dropping buffer head is missed again.
> 
> Second mount:
> ext4_fill_super
>  ext4_load_and_init_journal
>   ext4_load_journal
>    ext4_get_journal
>     jbd2_journal_init_inode
>      journal_init_common
>       bh = getblk_unmovable
>        bh = __find_get_block // Found stale bh in last failed mounting
>       journal->j_sb_buffer = bh
>    jbd2_journal_load
>     load_superblock
>      journal_get_superblock
>       if (buffer_verified(bh))
>       // true, skip journal->j_format_version = 2, value is 0
>     jbd2_journal_recover
>      do_one_pass
>       next_log_block += count_tags(journal, bh)
>       // According to journal_tag_bytes(), 'tag_bytes' calculating is
>       // affected by jbd2_has_feature_csum3(), jbd2_has_feature_csum3()
>       // returns false because 'j->j_format_version >= 2' is not true,
>       // then we get wrong next_log_block. The do_one_pass may exit
>       // early whenoccuring non JBD2_MAGIC_NUMBER in 'next_log_block'.
> 
> The filesystem is corrupted here, journal is partially replayed, and
> new journal sequence number actually is already used by last mounting.
> 
> The invalidate_bdev() can drop all buffer heads even racing with bare
> reading block device(eg. systemd-udev), so we can fix it by invalidating
> bdev in error handling path in __ext4_fill_super().
> 
> Fetch a reproducer in [Link].
> 
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=217171
> Cc: <stable@kernel.org>
> Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>

The fix looks good to me. Feel free to add:

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

								Honza

> ---
>  fs/ext4/super.c | 15 ++++++++-------
>  1 file changed, 8 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 88f7b8a88c76..7e990637bc48 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -1126,6 +1126,12 @@ static void ext4_blkdev_remove(struct ext4_sb_info *sbi)
>  	struct block_device *bdev;
>  	bdev = sbi->s_journal_bdev;
>  	if (bdev) {
> +		/*
> +		 * Invalidate the journal device's buffers.  We don't want them
> +		 * floating about in memory - the physical journal device may
> +		 * hotswapped, and it breaks the `ro-after' testing code.
> +		 */
> +		invalidate_bdev(bdev);
>  		ext4_blkdev_put(bdev);
>  		sbi->s_journal_bdev = NULL;
>  	}
> @@ -1271,14 +1277,8 @@ static void ext4_put_super(struct super_block *sb)
>  
>  	sync_blockdev(sb->s_bdev);
>  	invalidate_bdev(sb->s_bdev);
> -	if (sbi->s_journal_bdev && sbi->s_journal_bdev != sb->s_bdev) {
> -		/*
> -		 * Invalidate the journal device's buffers.  We don't want them
> -		 * floating about in memory - the physical journal device may
> -		 * hotswapped, and it breaks the `ro-after' testing code.
> -		 */
> +	if (sbi->s_journal_bdev) {
>  		sync_blockdev(sbi->s_journal_bdev);
> -		invalidate_bdev(sbi->s_journal_bdev);
>  		ext4_blkdev_remove(sbi);
>  	}
>  
> @@ -5610,6 +5610,7 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
>  	brelse(sbi->s_sbh);
>  	ext4_blkdev_remove(sbi);
>  out_fail:
> +	invalidate_bdev(sb->s_bdev);
>  	sb->s_fs_info = NULL;
>  	return err ? err : ret;
>  }
> -- 
> 2.31.1
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR