Date:   Tue, 2 Apr 2019 09:43:15 +0200
From:   Jan Kara <jack@suse.cz>
To:     Jiufei Xue <xuejiufei@gmail.com>
Cc:     Jiufei Xue <jiufei.xue@linux.alibaba.com>,
        linux-ext4@vger.kernel.org, tytso@mit.edu, jack@suse.cz,
        renzhen@linux.alibaba.com
Subject: Re: [PATCH v2] jbd2: check superblock mapped prior to committing
Message-ID: <20190402074315.GA12133@quack2.suse.cz>
References: <20190328100750.71045-1-jiufei.xue@linux.alibaba.com>
 <a406d83f-78a1-7f32-6ddb-9ec9df7a05ab@gmail.com>
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Hi,

On Tue 02-04-19 12:11:33, Jiufei Xue wrote:
> can I get your Acked-by?

Ted, tracks patches in patchwork and he processes less important fixes in
bigger batches when he has time. So don't be afraid, your patch is not lost
:)

								Honza

> 
> Thanks,
> Jiufei
> 
> On 2019/3/28 下午6:07, Jiufei Xue wrote:
> > We hit a BUG at fs/buffer.c:3057 if we detached the nbd device
> > before unmounting ext4 filesystem.
> >
> > The typical chain of events leading to the BUG:
> > jbd2_write_superblock
> >   submit_bh
> >     submit_bh_wbc
> >       BUG_ON(!buffer_mapped(bh));
> >
> > The block device is removed and all the pages are invalidated. JBD2
> > was trying to write journal superblock to the block device which is
> > no longer present.
> >
> > Fix this by checking the journal superblock's buffer head prior to
> > submitting.
> >
> > Cc: stable@kernel.org
> > Reported-by: Eric Ren <renzhen@linux.alibaba.com>
> > Signed-off-by: Jiufei Xue <jiufei.xue@linux.alibaba.com>
> > Reviewed-by: Jan Kara <jack@suse.cz>
> > ---
> >  fs/jbd2/journal.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
> > index 382c030cc78b..37e16d969925 100644
> > --- a/fs/jbd2/journal.c
> > +++ b/fs/jbd2/journal.c
> > @@ -1350,6 +1350,10 @@ static int jbd2_write_superblock(journal_t *journal, int write_flags)
> >  	journal_superblock_t *sb = journal->j_superblock;
> >  	int ret;
> >  
> > +	/* Buffer got discarded which means block device got invalidated */
> > +	if (!buffer_mapped(bh))
> > +		return -EIO;
> > +
> >  	trace_jbd2_write_superblock(journal, write_flags);
> >  	if (!(journal->j_flags & JBD2_BARRIER))
> >  		write_flags &= ~(REQ_FUA | REQ_PREFLUSH);
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR