Re: [PATCH v3 1/6] ext4: Fix reusing stale buffer heads from last failed mounting

Jan Kara
2023-03-15T08:43:49Z

On Wed 15-03-23 09:31:23, 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
> Fixes: 25ed6e8a54df ("jbd2: enable journal clients to enable v2 checksumming")
> Cc: stable@vger.kernel.org # v3.5
> Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>

Looks good. Feel free to add:

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

Honza

> ---
> fs/ext4/super.c | 13 +++++++------
> 1 file changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index f43e526112ae..61511b7ba017 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;
> }
> @@ -1272,13 +1278,7 @@ 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.
> - */
> 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