linux-kernel - [PATCH] [42/99] lockdep: Fix lock_is

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Message-Id: <20110727214841.156E72403FF@tassilo.jf.intel.com>
Date:	Wed, 27 Jul 2011 14:48:41 -0700 (PDT)
From:	Andi Kleen <andi@...stfloor.org>
To:	a.p.zijlstra@...llo.nl, torvalds@...ux-foundation.org,
	ak@...ux.intel.com, mingo@...e.hu, gregkh@...e.de,
	linux-kernel@...r.kernel.org, stable@...nel.org,
	tim.bird@...sony.com
Subject: [PATCH] [42/99] lockdep: Fix lock_is_held() on recursion

2.6.35-longterm review patch.  If anyone has any objections, please let me know.

------------------
From: Peter Zijlstra <a.p.zijlstra@...llo.nl>

commit f2513cde93f0957d5dc6c09bc24b0cccd27d8e1d upstream.

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>
Signed-off-by: Andi Kleen <ak@...ux.intel.com>
Link: http://lkml.kernel.org/r/1307398759.2497.966.camel@laptop
Signed-off-by: Ingo Molnar <mingo@...e.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 kernel/lockdep.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-2.6.35.y/kernel/lockdep.c
===================================================================
--- linux-2.6.35.y.orig/kernel/lockdep.c
+++ linux-2.6.35.y/kernel/lockdep.c
@@ -3250,7 +3250,7 @@ int lock_is_held(struct lockdep_map *loc
 	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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