[PATCH] lockdep: Fix lock_is_held on recursion

[PATCH] lockdep: Fix lock_is_held on recursion

[Peter Zijlstra]

Subject: lockdep: Fix lock_is_held on recursion
From: Peter Zijlstra <a.p.zijlstra@chello.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@die-jansens.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.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);

[tip:sched/urgent] lockdep: Fix lock_is_held() on recursion

[tip-bot for Peter Zijlstra]

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);

Re: [tip:sched/urgent] lockdep: Fix lock_is_held() on recursion

[Peter Zijlstra]

On Tue, 2011-06-07 at 12:02 +0000, tip-bot for Peter Zijlstra wrote:
> 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>

Not _that_ critical for stable since the offending lockdep_assert_held()
doesn't exist in .39, still definitely won't hurt.

Re: [tip:sched/urgent] lockdep: Fix lock_is_held() on recursion

[Ingo Molnar]

* Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:

> On Tue, 2011-06-07 at 12:02 +0000, tip-bot for Peter Zijlstra wrote:
> > 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>
> 
> Not _that_ critical for stable since the offending lockdep_assert_held()
> doesn't exist in .39, still definitely won't hurt.

Correct, the bug was hard enough to find, i didnt want someone else 
to trigger a similar one. There's numerous lockdep_assert_held() 
instances all around the tree.

Thanks,

	Ingo