2019-03-28 10:08:00

by Jiufei Xue

Subject: [PATCH v2] jbd2: check superblock mapped prior to committing

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: [email protected]
Reported-by: Eric Ren <[email protected]>
Signed-off-by: Jiufei Xue <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
---
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);
--
2.19.1.856.g8858448bb

2019-04-02 04:11:40

by Jiufei Xue

Subject: Re: [PATCH v2] jbd2: check superblock mapped prior to committing

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: [email protected]
> Reported-by: Eric Ren <[email protected]>
> Signed-off-by: Jiufei Xue <[email protected]>
> Reviewed-by: Jan Kara <[email protected]>
> ---
> 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);

2019-04-02 07:43:18

by Jan Kara

Subject: Re: [PATCH v2] jbd2: check superblock mapped prior to committing

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: [email protected]
> > Reported-by: Eric Ren <[email protected]>
> > Signed-off-by: Jiufei Xue <[email protected]>
> > Reviewed-by: Jan Kara <[email protected]>
> > ---
> > 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 <[email protected]>
SUSE Labs, CR

2019-04-07 02:14:01

by Theodore Ts'o

Subject: Re: [PATCH v2] jbd2: check superblock mapped prior to committing

On Thu, Mar 28, 2019 at 06:07:50PM +0800, 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.

Thanks, applied.

- Ted