[35/89] lockdep: Fix lock_is_held() on recursion

From: Greg KH
Date: Thu Jun 16 2011 - 03:37:04 EST

2.6.39-stable review patch. If anyone has any objections, please let us know.


From: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>

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@xxxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1307398759.2497.966.camel@laptop
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

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

--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -3242,7 +3242,7 @@ 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() */


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