Subject: Re: [PATCH v2] jbd2: check superblock mapped prior to committing
To:     Jiufei Xue <jiufei.xue@linux.alibaba.com>,
        linux-ext4@vger.kernel.org
Cc:     tytso@mit.edu, jack@suse.cz, renzhen@linux.alibaba.com
References: <20190328100750.71045-1-jiufei.xue@linux.alibaba.com>
From:   Jiufei Xue <xuejiufei@gmail.com>
Message-ID: <a406d83f-78a1-7f32-6ddb-9ec9df7a05ab@gmail.com>
Date:   Tue, 2 Apr 2019 12:11:33 +0800
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Hi Ted,

can I get your Acked-by?

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);