On Thu 28-03-19 17:18:14, 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@xxxxxxxxxx > Reported-by: Eric Ren <renzhen@xxxxxxxxxxxxxxxxx> > Signed-off-by: Jiufei Xue <jiufei.xue@xxxxxxxxxxxxxxxxx> > --- > fs/jbd2/journal.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c > index 382c030cc78b..90fd3ed0a232 100644 > --- a/fs/jbd2/journal.c > +++ b/fs/jbd2/journal.c > @@ -1350,6 +1350,9 @@ static int jbd2_write_superblock(journal_t *journal, int write_flags) > journal_superblock_t *sb = journal->j_superblock; > int ret; > Can you add a comment here like: /* Buffer got discarded which means block device got invalidated */ to explain what's going on? Thanks! Otherwise the patch looks good to me so you can add: Reviewed-by: Jan Kara <jack@xxxxxxx> Honza > + 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 > -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
