[PATCH RT 17/39] rtmutex.c: Fix incorrect waiter check

[Steven Rostedt]

3.14.34-rt32-rc1 stable review patch.
If anyone has any objections, please let me know.

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

From: Brad Mouring <bmouring@xxxxxx>

In task_blocks_on_lock, there's a null check on pi_blocked_on
of the task_struct. This pointer can encode the fact that the
task that contains the pointer is waking (preventing requeuing)
and therefore is non-null. Use the inline function to avoid
dereferencing an invalid "pointer"

Signed-off-by: Brad Mouring <brad.mouring@xxxxxx>
Reported-by: Ben Shelton <ben.shelton@xxxxxx>
Reviewed-by: T Makphaibulchoke <tmac@xxxxxx>
Tested-by: T Makphaibulchoke <tmac@xxxxxx>
Cc: stable-rt@xxxxxxxxxxxxxxx
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
---
 kernel/locking/rtmutex.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index ec72272ab73a..74a824523d3a 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -361,7 +361,8 @@ int max_lock_depth = 1024;
 
 static inline struct rt_mutex *task_blocked_on_lock(struct task_struct *p)
 {
-	return p->pi_blocked_on ? p->pi_blocked_on->lock : NULL;
+	return rt_mutex_real_waiter(p->pi_blocked_on) ?
+		p->pi_blocked_on->lock : NULL;
 }
 
 /*
-- 
2.1.4


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