[2.6.20.16 review 11/28] rt-mutex: Fix chain walk early wakeup bug

[Willy Tarreau <w@1wt.eu>]

[-- Attachment #1: 0011-rt-mutex-Fix-chain-walk-early-wakeup-bug.patch --]
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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 files changed, 13 insertions(+), 0 deletions(-)

diff --git a/kernel/rtmutex.c b/kernel/rtmutex.c
index 9b08847..dd5feae 100644
--- a/kernel/rtmutex.c
+++ b/kernel/rtmutex.c
@@ -212,6 +212,19 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
 	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;
-- 
1.5.2.4

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