linux-kernel - [PATCH -rt] rtmutex: enable deadlock detection in ww_mutex

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Message-ID: <20150127155642.GA21058@gbitten>
Date:	Tue, 27 Jan 2015 13:56:42 -0200
From:	Gustavo Bittencourt <gbitten@...il.com>
To:	linux-kernel@...r.kernel.org
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH -rt] rtmutex: enable deadlock detection in ww_mutex_lock
 functions

According the ww-mutex-design.txt documentation, the 
ww_mutex_lock_interruptible and ww_mutex_lock functions should return -EDEADLK
when faced with a deadlock. To do so, the detect_deadlock flag in the
rt_mutex_slowlock calls should be enabled. This patch corrects potential
deadlocks when running PREEMPT_RT with nouveau driver.

PS: Sorry to post again, CC'ing -rt maintainers now.

Signed-off-by: Gustavo Bittencourt <gbitten@...il.com>
---
 kernel/locking/rtmutex.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 6c40660..3f6ef91 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -1965,7 +1965,7 @@ __ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ww_c
 	might_sleep();
 
 	mutex_acquire(&lock->base.dep_map, 0, 0, _RET_IP_);
-	ret = rt_mutex_slowlock(&lock->base.lock, TASK_INTERRUPTIBLE, NULL, 0, ww_ctx);
+	ret = rt_mutex_slowlock(&lock->base.lock, TASK_INTERRUPTIBLE, NULL, 1, ww_ctx);
 	if (ret)
 		mutex_release(&lock->base.dep_map, 1, _RET_IP_);
 	else if (!ret && ww_ctx->acquired > 1)
@@ -1984,7 +1984,7 @@ __ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ww_ctx)
 
 	mutex_acquire_nest(&lock->base.dep_map, 0, 0, &ww_ctx->dep_map,
 			_RET_IP_);
-	ret = rt_mutex_slowlock(&lock->base.lock, TASK_UNINTERRUPTIBLE, NULL, 0, ww_ctx);
+	ret = rt_mutex_slowlock(&lock->base.lock, TASK_UNINTERRUPTIBLE, NULL, 1, ww_ctx);
 	if (ret)
 		mutex_release(&lock->base.dep_map, 1, _RET_IP_);
 	else if (!ret && ww_ctx->acquired > 1)
-- 
1.9.1

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