check-superblock-mapped-prior-to-committing

   1 jbd2: check superblock mapped prior to committing
   2
   3 From: Jiufei Xue <jiufei.xue@linux.alibaba.com>
   4
   5 We hit a BUG at fs/buffer.c:3057 if we detached the nbd device
   6 before unmounting ext4 filesystem.
   7
   8 The typical chain of events leading to the BUG:
   9 jbd2_write_superblock
  10   submit_bh
  11     submit_bh_wbc
  12       BUG_ON(!buffer_mapped(bh));
  13
  14 The block device is removed and all the pages are invalidated. JBD2
  15 was trying to write journal superblock to the block device which is
  16 no longer present.
  17
  18 Fix this by checking the journal superblock's buffer head prior to
  19 submitting.
  20
  21 Reported-by: Eric Ren <renzhen@linux.alibaba.com>
  22 Signed-off-by: Jiufei Xue <jiufei.xue@linux.alibaba.com>
  23 Signed-off-by: Theodore Ts'o <tytso@mit.edu>
  24 Reviewed-by: Jan Kara <jack@suse.cz>
  25 Cc: stable@kernel.org
  26 ---
  27  fs/jbd2/journal.c | 4 ++++
  28  1 file changed, 4 insertions(+)
  29
  30 diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
  31 index 382c030cc78b..37e16d969925 100644
  32 --- a/fs/jbd2/journal.c
  33 +++ b/fs/jbd2/journal.c
  34 @@ -1350,6 +1350,10 @@ static int jbd2_write_superblock(journal_t *journal, int write_flags)
  35         journal_superblock_t *sb = journal->j_superblock;
  36         int ret;
  37
  38 +       /* Buffer got discarded which means block device got invalidated */
  39 +       if (!buffer_mapped(bh))
  40 +               return -EIO;
  41 +
  42         trace_jbd2_write_superblock(journal, write_flags);
  43         if (!(journal->j_flags & JBD2_BARRIER))
  44                 write_flags &= ~(REQ_FUA | REQ_PREFLUSH);
  45 --
  46 2.19.1.856.g8858448bb
  47
  48