#From oleg@tv-sign.ru Mon Jan  7 18:30:05 2008
#Date: Mon, 7 Jan 2008 20:22:39 +0300
#From: Oleg Nesterov <oleg@tv-sign.ru>
#To: Peter Zijlstra <a.p.zijlstra@chello.nl>
#Cc: Herbert Xu <herbert@gondor.apana.org.au>, Ingo Molnar <mingo@elte.hu>, Rafael J. Wysocki <rjw@sisk.pl>, Christian Kujau <lists@nerdbynature.de>, linux-kernel@vger.kernel.org, jfs-discussion@lists.sourceforge.net, Davide Libenzi <davidel@xmailserver.org>, Johannes Berg <johannes@sipsolutions.net>
#Subject: Re: 2.6.24-rc6: possible recursive locking detected
#
#On 01/05, Peter Zijlstra wrote:
#>
#> Since EP_MAX_POLLWAKE_NESTS < MAX_LOCKDEP_SUBCLASSES we could perhaps do
#> something like:
#>
#>   wake_up_nested(..., wake_nests);
#
#I think this would be the most correct change. But I wonder if it is possible
#to do something more generic (but otoh more stupid/hackish and less safe).
#
#Consider this "just for illustration" patch,
#
--- t/kernel/lockdep.c	2007-11-09 12:57:31.000000000 +0300
+++ t/kernel/lockdep.c	2008-01-07 19:43:50.000000000 +0300
@@ -1266,10 +1266,13 @@ check_deadlock(struct task_struct *curr,
 	struct held_lock *prev;
 	int i;
 
-	for (i = 0; i < curr->lockdep_depth; i++) {
+	for (i = curr->lockdep_depth; --i >= 0; ) {
 		prev = curr->held_locks + i;
 		if (prev->class != next->class)
 			continue;
+
+		if (prev->trylock == -1)
+			return 2;
 		/*
 		 * Allow read-after-read recursion of the same
 		 * lock class (i.e. read_lock(lock)+read_lock(lock)):