linux-kernel - [tip/urgent] Avoid deadlock in rt_mutex_start_proxy

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Message-ID: <4A79D7F1.4000405@us.ibm.com>
Date:	Wed, 05 Aug 2009 12:05:21 -0700
From:	Darren Hart <dvhltc@...ibm.com>
To:	"lkml, " <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...e.hu>,
	Dinakar Guniguntala <dino@...ibm.com>,
	John Stultz <johnstul@...ux.vnet.ibm.com>
Subject: [tip/urgent] Avoid deadlock in rt_mutex_start_proxy_lock()

From: Darren Hart <dvhltc@...ibm.com>

In the event of a lock steal or owner died, rt_mutex_start_proxy_lock() will
give the rt_mutex to the waiting task, but it fails to release the wait_lock.
This leads to subsequent deadlocks when other tasks try to acquire the
rt_mutex.

I also removed a few extra blank lines that really spaced this routine out.
I must have been high on the \n when I wrote this originally...

Note: This is the mainline version, a separate patch was sent for [RT]

Signed-off-by: Darren Hart <dvhltc@...ibm.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Ingo Molnar <mingo@...e.hu>
CC: Dinakar Guniguntala <dino@...ibm.com>
CC: John Stultz <johnstul@...ibm.com>
---

 kernel/rtmutex.c |    4 +---
 1 files changed, 1 insertions(+), 3 deletions(-)


diff --git a/kernel/rtmutex.c b/kernel/rtmutex.c
index fec77e7..0f2b9bb 100644
--- a/kernel/rtmutex.c
+++ b/kernel/rtmutex.c
@@ -1039,16 +1039,14 @@ int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
 	if (!rt_mutex_owner(lock) || try_to_steal_lock(lock, task)) {
 		/* We got the lock for task. */
 		debug_rt_mutex_lock(lock);
-
 		rt_mutex_set_owner(lock, task, 0);
-
+		spin_unlock(&lock->wait_lock);
 		rt_mutex_deadlock_account_lock(lock, task);
 		return 1;
 	}
 
 	ret = task_blocks_on_rt_mutex(lock, waiter, task, detect_deadlock);
 
-
 	if (ret && !waiter->task) {
 		/*
 		 * Reset the return value. We might have
-- 
Darren Hart
IBM Linux Technology Center
Real-Time Linux Team
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