Re: [PATCH] ext4: don't BUG on inconsistent journal feature

[Lukas Czerner <lczerner@redhat.com>]

On Thu, Jul 09, 2020 at 11:58:54AM +0200, Jan Kara wrote:
> A customer has reported a BUG_ON in ext4_clear_journal_err() hitting
> during an LTP testing. Either this has been caused by a test setup
> issue where the filesystem was being overwritten while LTP was mounting
> it or the journal replay has overwritten the superblock with invalid
> data. In either case it is preferable we don't take the machine down
> with a BUG_ON. So handle the situation of unexpectedly missing
> has_journal feature more gracefully by a WARN_ON_ONCE and bailing out
> with error.
> 
> Signed-off-by: Jan Kara <jack@suse.cz>
> ---
>  fs/ext4/super.c | 35 ++++++++++++++++++++++++-----------
>  1 file changed, 24 insertions(+), 11 deletions(-)
> 
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 330957ed1f05..d8b7222cb86c 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -68,8 +68,8 @@ static int ext4_show_options(struct seq_file *seq, struct dentry *root);
>  static int ext4_commit_super(struct super_block *sb, int sync);
>  static void ext4_mark_recovery_complete(struct super_block *sb,
>  					struct ext4_super_block *es);
> -static void ext4_clear_journal_err(struct super_block *sb,
> -				   struct ext4_super_block *es);
> +static int ext4_clear_journal_err(struct super_block *sb,
> +				  struct ext4_super_block *es);
>  static int ext4_sync_fs(struct super_block *sb, int wait);
>  static int ext4_remount(struct super_block *sb, int *flags, char *data);
>  static int ext4_statfs(struct dentry *dentry, struct kstatfs *buf);
> @@ -4956,7 +4956,8 @@ static journal_t *ext4_get_journal(struct super_block *sb,
>  	struct inode *journal_inode;
>  	journal_t *journal;
>  
> -	BUG_ON(!ext4_has_feature_journal(sb));
> +	if (WARN_ON_ONCE(!ext4_has_feature_journal(sb)))
> +		return NULL;
>  
>  	journal_inode = ext4_get_journal_inode(sb, journal_inum);
>  	if (!journal_inode)
> @@ -4986,7 +4987,8 @@ static journal_t *ext4_get_dev_journal(struct super_block *sb,
>  	struct ext4_super_block *es;
>  	struct block_device *bdev;
>  
> -	BUG_ON(!ext4_has_feature_journal(sb));
> +	if (WARN_ON_ONCE(!ext4_has_feature_journal(sb)))
> +		return NULL;
>  
>  	bdev = ext4_blkdev_get(j_dev, sb);
>  	if (bdev == NULL)
> @@ -5078,7 +5080,8 @@ static int ext4_load_journal(struct super_block *sb,
>  	int err = 0;
>  	int really_read_only;
>  
> -	BUG_ON(!ext4_has_feature_journal(sb));
> +	if (WARN_ON_ONCE(!ext4_has_feature_journal(sb)))
> +		return -EFSCORRUPTED;
>  
>  	if (journal_devnum &&
>  	    journal_devnum != le32_to_cpu(es->s_journal_dev)) {
> @@ -5148,7 +5151,12 @@ static int ext4_load_journal(struct super_block *sb,
>  	}
>  
>  	EXT4_SB(sb)->s_journal = journal;
> -	ext4_clear_journal_err(sb, es);
> +	err = ext4_clear_journal_err(sb, es);
> +	if (err) {
> +		EXT4_SB(sb)->s_journal = NULL;
> +		jbd2_journal_destroy(journal);
> +		return err;
> +	}
>  
>  	if (!really_read_only && journal_devnum &&
>  	    journal_devnum != le32_to_cpu(es->s_journal_dev)) {
> @@ -5250,7 +5258,7 @@ static void ext4_mark_recovery_complete(struct super_block *sb,
>  	journal_t *journal = EXT4_SB(sb)->s_journal;
>  
>  	if (!ext4_has_feature_journal(sb)) {
> -		BUG_ON(journal != NULL);
> +		WARN_ON_ONCE(journal != NULL);

Hi Jan,

If this ever happens we will hapily continue with fs operation after
mount, or remount (remount is ro, so that is probably ok ?) without
journal feature, but with s_journal set ? I am not quite sure what the
consequences might be, are you sure this is ok ?

-Lukas

>  		return;
>  	}
>  	jbd2_journal_lock_updates(journal);
> @@ -5271,14 +5279,15 @@ static void ext4_mark_recovery_complete(struct super_block *sb,
>   * has recorded an error from a previous lifetime, move that error to the
>   * main filesystem now.
>   */
> -static void ext4_clear_journal_err(struct super_block *sb,
> +static int ext4_clear_journal_err(struct super_block *sb,
>  				   struct ext4_super_block *es)
>  {
>  	journal_t *journal;
>  	int j_errno;
>  	const char *errstr;
>  
> -	BUG_ON(!ext4_has_feature_journal(sb));
> +	if (WARN_ON_ONCE(!ext4_has_feature_journal(sb)))
> +		return -EFSCORRUPTED;
>  
>  	journal = EXT4_SB(sb)->s_journal;
>  
> @@ -5303,6 +5312,7 @@ static void ext4_clear_journal_err(struct super_block *sb,
>  		jbd2_journal_clear_err(journal);
>  		jbd2_journal_update_sb_errno(journal);
>  	}
> +	return 0;
>  }
>  
>  /*
> @@ -5622,8 +5632,11 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data)
>  			 * been changed by e2fsck since we originally mounted
>  			 * the partition.)
>  			 */
> -			if (sbi->s_journal)
> -				ext4_clear_journal_err(sb, es);
> +			if (sbi->s_journal) {
> +				err = ext4_clear_journal_err(sb, es);
> +				if (err)
> +					goto restore_opts;
> +			}
>  			sbi->s_mount_state = le16_to_cpu(es->s_state);
>  
>  			err = ext4_setup_super(sb, es, 0);
> -- 
> 2.16.4
>