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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@chello.nl>
AuthorDate: Mon, 6 Jun 2011 12:32:43 +0200
Committer: Ingo Molnar <mingo@elte.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@die-jansens.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: <stable@kernel.org>
Link: http://lkml.kernel.org/r/1307398759.2497.966.camel@laptop
Signed-off-by: Ingo Molnar <mingo@elte.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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