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    Subject[ 21/37] jbd: Fix lock ordering bug in journal_unmap_buffer()
    Date
    3.0-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Jan Kara <jack@suse.cz>

    commit 25389bb207987b5774182f763b9fb65ff08761c8 upstream.

    Commit 09e05d48 introduced a wait for transaction commit into
    journal_unmap_buffer() in the case we are truncating a buffer undergoing commit
    in the page stradding i_size on a filesystem with blocksize < pagesize. Sadly
    we forgot to drop buffer lock before waiting for transaction commit and thus
    deadlock is possible when kjournald wants to lock the buffer.

    Fix the problem by dropping the buffer lock before waiting for transaction
    commit. Since we are still holding page lock (and that is OK), buffer cannot
    disappear under us.

    Signed-off-by: Jan Kara <jack@suse.cz>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/jbd/transaction.c | 2 ++
    1 file changed, 2 insertions(+)

    --- a/fs/jbd/transaction.c
    +++ b/fs/jbd/transaction.c
    @@ -1955,7 +1955,9 @@ retry:
    spin_unlock(&journal->j_list_lock);
    jbd_unlock_bh_state(bh);
    spin_unlock(&journal->j_state_lock);
    + unlock_buffer(bh);
    log_wait_commit(journal, tid);
    + lock_buffer(bh);
    goto retry;
    }
    /*



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