There are a couple of blocked on type structures. One for mutexes, and one
for rtmutexes, and we also need one for futexes.

Instead of just adding another one to the task struct I combined them all into
a union. Since a waiter can only be blocked on one of the types at any given
time this should be safe.

I also usurped the pi_lock as the lock which protects all the blocked_on types.

Signed-off-by: Daniel Walker <dwalker@mvista.com>

---
 include/linux/sched.h |   36 +++++++++++++++++++++++++++++++-----
 kernel/fork.c         |    2 --
 kernel/mutex-debug.c  |   25 ++++++++++++++++++-------
 kernel/mutex-debug.h  |    4 +++-
 kernel/mutex.c        |    6 +++++-
 5 files changed, 57 insertions(+), 16 deletions(-)

Index: linux-2.6.25/include/linux/sched.h
===================================================================
--- linux-2.6.25.orig/include/linux/sched.h
+++ linux-2.6.25/include/linux/sched.h
@@ -1024,6 +1024,17 @@ struct sched_rt_entity {
 #endif
 };
 
+enum lock_waiter_type {
+	MUTEX_WAITER = 1,
+};
+
+struct lock_waiter_state {
+	enum lock_waiter_type lock_type;
+	union {
+		struct mutex_waiter *mutex_blocked_on;
+	};
+};
+
 struct task_struct {
 	volatile long state;	/* -1 unrunnable, 0 runnable, >0 stopped */
 	void *stack;
@@ -1201,7 +1212,7 @@ struct task_struct {
 /* Protection of (de-)allocation: mm, files, fs, tty, keyrings */
 	spinlock_t alloc_lock;
 
-	/* Protection of the PI data structures: */
+	/* Protects blocked_on field and PI waiters list. */
 	spinlock_t pi_lock;
 
 #ifdef CONFIG_RT_MUTEXES
@@ -1211,10 +1222,12 @@ struct task_struct {
 	struct rt_mutex_waiter *pi_blocked_on;
 #endif
 
-#ifdef CONFIG_DEBUG_MUTEXES
-	/* mutex deadlock detection */
-	struct mutex_waiter *blocked_on;
-#endif
+	/*
+	 * Deadlock detection and priority inheritance handling,
+	 * and any other out of line mutex operations
+	 */
+	struct lock_waiter_state *blocked_on;
+
 #ifdef CONFIG_TRACE_IRQFLAGS
 	unsigned int irq_events;
 	int ...
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Now you grew task_struct unconditionally, how about

#if defined CONFIG_DEBUG_MUTEX || defined CONFIG_RT_MUTEXES || defined CONFIG_FUTEX

?

--

[ message continues ]

Ok .. I didn't add it cause I wasn't convinced RT_MUTEXES was
optional .. There's a lot of PI futex related code that isn't ifdef'd
either..

Daniel

--

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