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>

diff --git a/fs/jbd/transaction.c b/fs/jbd/transaction.c
index b0161a66d35aeb5a5a7032ec3ba7b5d7a036fe1c..d7ab0926832ed6bfaac22154563bf2a68a5fcd0d 100644 (file)
--- 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;
                }
                /*