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Date:   Thu, 9 Jul 2020 17:15:53 +0200
From:   Jan Kara <jack@...e.cz>
To:     Lukas Czerner <lczerner@...hat.com>
Cc:     Jan Kara <jack@...e.cz>, Ted Tso <tytso@....edu>,
        linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: don't BUG on inconsistent journal feature

On Thu 09-07-20 14:36:55, Lukas Czerner wrote:
> 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@...e.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 Lukas!

> 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 ?

Hum, you're right we should probably fail the mount... In fact looking into
this now, we should probably also handle this situation with ext4_error() so
that filesystem gets marked as corrupted and all that. Thanks for feedback.
I'll rework the patch.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR

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