reiserfs, kill-the-BKL: fix unsafe j_flush_mutex lock

Impact: fix a deadlock

The j_flush_mutex is acquired safely in journal.c:
if we can't take it, we free the reiserfs per superblock lock
and wait a bit.

But we have a remaining place in kupdate_transactions() where
j_flush_mutex is still acquired traditionnaly. Thus the following
scenario (warned by lockdep) can happen:

A						B

mutex_lock(&write_lock)			mutex_lock(&write_lock)
	mutex_lock(&j_flush_mutex)	mutex_lock(&j_flush_mutex) //block
	mutex_unlock(&write_lock)
	sleep...
	mutex_lock(&write_lock) //deadlock

Fix this by using reiserfs_mutex_lock_safe() in kupdate_transactions().
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Cc: Alessio Igor Bogani <abogani@texware.it>
Cc: Jeff Mahoney <jeffm@suse.com>
LKML-Reference: <1239660635-12940-1-git-send-email-fweisbec@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

fs/reiserfs/journal.c

@@ -1826,7 +1826,7 @@ static int kupdate_transactions(struct super_block *s,
 	struct reiserfs_journal *journal = SB_JOURNAL(s);
 	chunk.nr = 0;
 
-	mutex_lock(&journal->j_flush_mutex);
+	reiserfs_mutex_lock_safe(&journal->j_flush_mutex, s);
 	if (!journal_list_still_alive(s, orig_trans_id)) {
 		goto done;
 	}