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jbd2: check superblock mapped prior to committing

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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.

Reported-by: Eric Ren <[email protected]>
Signed-off-by: Jiufei Xue <[email protected]>
Signed-off-by: Theodore Ts'o <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Cc: [email protected]
This commit is contained in:
Jiufei Xue authored and Theodore Ts'o committed 2019-04-06 18:57:40 -04:00
1 parent fe53cbc5a3
commit 742b06b562
1 file changed
+4
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fs/jbd2/journal.c
+4
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@@ -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);