linux-kernel - [tip:sched/urgent] lockdep: Fix lock_is

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Date:	Tue, 7 Jun 2011 12:02:29 GMT
From:	tip-bot for Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...hat.com,
	torvalds@...ux-foundation.org, a.p.zijlstra@...llo.nl,
	lists@...-jansens.de, stable@...nel.org, tglx@...utronix.de,
	mingo@...e.hu
Subject: [tip:sched/urgent] lockdep: Fix lock_is_held() on recursion

Commit-ID:  f2513cde93f0957d5dc6c09bc24b0cccd27d8e1d
Gitweb:     http://git.kernel.org/tip/f2513cde93f0957d5dc6c09bc24b0cccd27d8e1d
Author:     Peter Zijlstra <a.p.zijlstra@...llo.nl>
AuthorDate: Mon, 6 Jun 2011 12:32:43 +0200
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Tue, 7 Jun 2011 12:25:50 +0200

lockdep: Fix lock_is_held() on recursion

The main lock_is_held() user is lockdep_assert_held(), avoid false
assertions in lockdep_off() sections by unconditionally reporting the
lock is taken.

[ the reason this is important is a lockdep_assert_held() in ttwu()
  which triggers a warning under lockdep_off() as in printk() which
  can trigger another wakeup and lock up due to spinlock
  recursion, as reported and heroically debugged by Arne Jansen ]

Reported-and-tested-by: Arne Jansen <lists@...-jansens.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: <stable@...nel.org>
Link: http://lkml.kernel.org/r/1307398759.2497.966.camel@laptop
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 kernel/lockdep.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index 63437d0..298c927 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -3426,7 +3426,7 @@ int lock_is_held(struct lockdep_map *lock)
 	int ret = 0;
 
 	if (unlikely(current->lockdep_recursion))
-		return ret;
+		return 1; /* avoid false negative lockdep_assert_held() */
 
 	raw_local_irq_save(flags);
 	check_flags(flags);
--
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