Commit 742b06b5 authored Apr 06, 2019 by Jiufei Xue Committed by Theodore Ts'o Apr 06, 2019

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.

Reported-by: Eric Ren <renzhen@linux.alibaba.com>
Signed-off-by: Jiufei Xue <jiufei.xue@linux.alibaba.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: stable@kernel.org

parent fe53cbc5

fs/jbd2/journal.c

+4 −0

Original line number	Diff line number	Diff line
		@@ -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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