[patch 04/26] rt-mutex: Fix chain walk early wakeup bug

[Greg KH <gregkh@suse.de>]

[-- Attachment #1: rt-mutex-fix-chain-walk-early-wakeup-bug.patch --]
[-- Type: text/plain, Size: 1325 bytes --]


-stable review patch.  If anyone has any objections, please let us know.

------------------

Alexey Kuznetsov found some problems in the pi-futex code. 

One of the root causes is:

When a wakeup happens, we do not to stop the chain walk so we
we follow a non existing locking chain.

Drop out when this happens.

Cc: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
 kernel/rtmutex.c |   13 +++++++++++++
 1 file changed, 13 insertions(+)

--- linux-2.6.21.6.orig/kernel/rtmutex.c
+++ linux-2.6.21.6/kernel/rtmutex.c
@@ -212,6 +212,19 @@ static int rt_mutex_adjust_prio_chain(st
 	if (!waiter || !waiter->task)
 		goto out_unlock_pi;
 
+	/*
+	 * Check the orig_waiter state. After we dropped the locks,
+	 * the previous owner of the lock might have released the lock
+	 * and made us the pending owner:
+	 */
+	if (orig_waiter && !orig_waiter->task)
+		goto out_unlock_pi;
+
+	/*
+	 * Drop out, when the task has no waiters. Note,
+	 * top_waiter can be NULL, when we are in the deboosting
+	 * mode!
+	 */
 	if (top_waiter && (!task_has_pi_waiters(task) ||
 			   top_waiter != task_top_pi_waiter(task)))
 		goto out_unlock_pi;

--