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Subject[PATCH] [42/99] lockdep: Fix lock_is_held() on recursion
Date
2.6.35-longterm review patch.  If anyone has any objections, please let me know.

------------------
From: Peter Zijlstra <a.p.zijlstra@chello.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@die-jansens.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Link: http://lkml.kernel.org/r/1307398759.2497.966.camel@laptop
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.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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