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From: Peter Zijlstra <peterz@infradead.org>
To: Jason Low <jason.low2@hp.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>,
	"Michael L. Semon" <mlsemon35@gmail.com>,
	Ingo Molnar <mingo@kernel.org>,
	linux-kernel@vger.kernel.org
Subject: Re: 3.14.0+/x86: lockdep and mutexes not getting along
Date: Thu, 10 Apr 2014 16:15:59 +0200
Message-ID: <20140410141559.GE13658@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20140410091824.GL10526@twins.programming.kicks-ass.net>

On Thu, Apr 10, 2014 at 11:18:24AM +0200, Peter Zijlstra wrote:
> So I managed to reproduce, and the below makes it go away. I just don't
> understand why though. will stare more.

/me kicks himself.. bloody obvious fail there :-)

Not unlocking the lock after a lockdep trigger will make things get
stuck real fast :-)

---
 kernel/locking/mutex-debug.c | 19 +++++++++----------
 1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/kernel/locking/mutex-debug.c b/kernel/locking/mutex-debug.c
index e1191c996c59..5cf6731b98e9 100644
--- a/kernel/locking/mutex-debug.c
+++ b/kernel/locking/mutex-debug.c
@@ -71,18 +71,17 @@ void mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *waiter,
 
 void debug_mutex_unlock(struct mutex *lock)
 {
-	if (unlikely(!debug_locks))
-		return;
+	if (likely(debug_locks)) {
+		DEBUG_LOCKS_WARN_ON(lock->magic != lock);
 
-	DEBUG_LOCKS_WARN_ON(lock->magic != lock);
+		if (!lock->owner)
+			DEBUG_LOCKS_WARN_ON(!lock->owner);
+		else
+			DEBUG_LOCKS_WARN_ON(lock->owner != current);
 
-	if (!lock->owner)
-		DEBUG_LOCKS_WARN_ON(!lock->owner);
-	else
-		DEBUG_LOCKS_WARN_ON(lock->owner != current);
-
-	DEBUG_LOCKS_WARN_ON(!lock->wait_list.prev && !lock->wait_list.next);
-	mutex_clear_owner(lock);
+		DEBUG_LOCKS_WARN_ON(!lock->wait_list.prev && !lock->wait_list.next);
+		mutex_clear_owner(lock);
+	}
 
 	/*
 	 * __mutex_slowpath_needs_to_unlock() is explicitly 0 for debug

  reply index

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-04-06  5:12 Michael L. Semon
2014-04-09 12:19 ` Kirill A. Shutemov
2014-04-10  5:42   ` Jason Low
2014-04-10  8:14     ` Peter Zijlstra
2014-04-10  9:15     ` Kirill A. Shutemov
2014-04-10 11:42       ` Peter Zijlstra
2014-04-10  9:18     ` Peter Zijlstra
2014-04-10 14:15       ` Peter Zijlstra [this message]
2014-04-11 13:59         ` Valdis.Kletnieks
2014-04-14  7:22         ` [tip:core/urgent] locking/mutex: Fix debug_mutexes tip-bot for Peter Zijlstra
2014-04-10 17:14       ` 3.14.0+/x86: lockdep and mutexes not getting along Jason Low
2014-04-10 17:28         ` Peter Zijlstra
2014-04-10 19:04           ` Jason Low
2014-04-10 23:26         ` Dave Jones
2014-04-10 23:30           ` Dave Jones
2014-04-11  3:48           ` Paul E. McKenney
2014-04-11 13:41     ` Michael L. Semon
2014-04-10  8:12   ` Peter Zijlstra
2014-04-10  8:13   ` Peter Zijlstra
2014-04-10 14:29   ` cred_guard_mutex vs seq_file::lock [was: Re: 3.14.0+/x86: lockdep and mutexes not getting along] Peter Zijlstra
2014-04-11 14:50   ` David Howells
2014-04-11 15:07     ` Al Viro
2014-07-30 22:31       ` Kirill A. Shutemov
2014-07-30 23:03         ` Kirill A. Shutemov
2014-07-31  7:26         ` Cyrill Gorcunov

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