jbd: Fix lock ordering bug in journal_unmap_buffer()

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>
Signed-off-by: Willy Tarreau <w@1wt.eu>

diff --git a/fs/jbd/transaction.c b/fs/jbd/transaction.c
index 4eff79cc575187d2e91fa5e6a66f6883f060b558..1352e60bd234e553064bf58a81c9580b0b37b97d 100644 (file)
--- a/fs/jbd/transaction.c
+++ b/fs/jbd/transaction.c
@@ -1956,7 +1956,9 @@ 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;
                }
                /*