linux-kernel - [PATCH] lockdep: Fix lock_is

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Date:	Tue, 07 Jun 2011 00:19:19 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Arne Jansen <lists@...-jansens.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	efault@....de, npiggin@...nel.dk, akpm@...ux-foundation.org,
	frank.rowand@...sony.com, tglx <tglx@...utronix.de>
Subject: [PATCH] lockdep: Fix lock_is_held on recursion

Subject: lockdep: Fix lock_is_held on recursion
From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Date: Mon Jun 06 12:32:43 CEST 2011

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 ]

Reported-and-tested-by: Arne Jansen <lists@...-jansens.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
---
Index: linux-2.6/kernel/lockdep.c
===================================================================
--- linux-2.6.orig/kernel/lockdep.c
+++ linux-2.6/kernel/lockdep.c
@@ -3426,7 +3426,7 @@ 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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