Commit c2a50e04 authored by Jiufei Xue's avatar Jiufei Xue Committed by Greg Kroah-Hartman

jbd2: check superblock mapped prior to committing

commit 742b06b5 upstream.

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: default avatarEric Ren <renzhen@linux.alibaba.com>
Signed-off-by: default avatarJiufei Xue <jiufei.xue@linux.alibaba.com>
Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
Reviewed-by: default avatarJan Kara <jack@suse.cz>
Cc: stable@kernel.org
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent ed1d236d
......@@ -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);
......
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