Re: 2.6.13-rt3

[Steven Rostedt <rostedt@goodmis.org>]

Ingo,

I just found a __MAJOR__ bug in my code.  Below is the patch that fixes
this bug,  zaps the WARN_ON in check_pi_list_present, and changes
ALL_TASKS_PI to a booleon instead of just a define.

The major bug was in __down_trylock.  See anything wrong with this
code :-)  I'm surprised that this worked as well as it did!


	if (likely(!old_owner) || __grab_lock(lock, task, old_owner->task)) {
		/* granted */
		TRACE_WARN_ON_LOCKED(!plist_empty(&lock->wait_list) && !old_owner);
		if (old_owner) {
			__raw_spin_lock(&old_owner->task->pi_lock);
			set_new_owner(lock, old_owner, ti __EIP__);
			__raw_spin_unlock(&old_owner->task->pi_lock);
		} else
			set_new_owner(lock, old_owner, ti __EIP__);
		__raw_spin_unlock(&lock->wait_lock);
		__raw_spin_unlock(&task->pi_lock);
		ret = 1;
	}
	__raw_spin_unlock(&lock->wait_lock);
	__raw_spin_unlock(&task->pi_lock);


Here's the patch:

-- Steve

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

Index: linux_realtime_goliath/kernel/rt.c
===================================================================
--- linux_realtime_goliath/kernel/rt.c	(revision 314)
+++ linux_realtime_goliath/kernel/rt.c	(working copy)
@@ -104,7 +104,7 @@
  * in the system fall under PI handling. Normally only SCHED_FIFO/RR
  * tasks are PI-handled:
  */
-#define ALL_TASKS_PI
+#define ALL_TASKS_PI 1
 
 #ifdef CONFIG_RT_DEADLOCK_DETECT
 # define __EIP_DECL__ , unsigned long eip
@@ -663,7 +663,7 @@
 
 #endif
 
-#if defined(ALL_TASKS_PI) && defined(CONFIG_RT_DEADLOCK_DETECT)
+#if ALL_TASKS_PI && defined(CONFIG_RT_DEADLOCK_DETECT)
 
 static void
 check_pi_list_present(struct rt_mutex *lock, struct rt_mutex_waiter *waiter,
@@ -674,7 +674,6 @@
 
 	__raw_spin_lock(&old_owner->task->pi_lock);
 	TRACE_WARN_ON_LOCKED(plist_empty(&waiter->pi_list));
-	TRACE_WARN_ON_LOCKED(lock_owner(lock));
 
 	plist_for_each(curr1, &old_owner->task->pi_waiters) {
 		w = plist_entry(curr1, struct rt_mutex_waiter, pi_list);
@@ -851,7 +850,7 @@
 			__raw_spin_lock(&l->wait_lock);
 
 		TRACE_BUG_ON_LOCKED(!lock_owner(l));
-		if (rt_task(p) && plist_empty(&w->pi_list)) {
+		if ((ALL_TASKS_PI || rt_task(p)) && plist_empty(&w->pi_list)) {
 			TRACE_BUG_ON_LOCKED(was_rt);
 			plist_init(&w->pi_list, prio);
 			plist_add(&w->pi_list, &lock_owner(l)->task->pi_waiters);
@@ -868,7 +867,7 @@
 		 * (TODO: this can be unfair to SCHED_NORMAL tasks if they
 		 *        get PI handled.)
 		 */
-		if (!rt_task(p) && !plist_empty(&w->pi_list)) {
+		if (!ALL_TASKS_PI && !rt_task(p) && !plist_empty(&w->pi_list)) {
 			TRACE_BUG_ON_LOCKED(!was_rt);
 			plist_del(&w->pi_list, &lock_owner(l)->task->pi_waiters);
 			plist_del(&w->list, &l->wait_list);
@@ -970,7 +969,7 @@
 	 */
 	TRACE_BUG_ON_LOCKED(!spin_is_locked(&task->pi_lock));
 	TRACE_BUG_ON_LOCKED(!spin_is_locked(&lock->wait_lock));
-#ifndef ALL_TASKS_PI
+#if !ALL_TASKS_PI
 	if (!rt_task(task)) {
 		plist_add(&waiter->list, &lock->wait_list);
 		set_lock_owner_pending(lock);
@@ -1071,6 +1070,7 @@
 	struct rt_mutex_waiter *waiter = NULL;
 	struct thread_info *new_owner;
 
+	TRACE_BUG_ON_LOCKED(!spin_is_locked(&lock->wait_lock));
 	/*
 	 * Get the highest prio one:
 	 *
@@ -1083,7 +1083,7 @@
 #endif
 	trace_special_pid(waiter->ti->task->pid, waiter->ti->task->prio, 0);
 
-#ifdef ALL_TASKS_PI
+#if ALL_TASKS_PI
 	check_pi_list_present(lock, waiter, old_owner);
 #endif
 	new_owner = waiter->ti;
@@ -1543,7 +1543,7 @@
 	list_del_init(&lock->held_list);
 #endif
 
-#ifdef ALL_TASKS_PI
+#if ALL_TASKS_PI
 	if (plist_empty(&lock->wait_list))
 		check_pi_list_empty(lock, lock_owner(lock));
 #endif
@@ -1906,8 +1906,6 @@
 			__raw_spin_unlock(&old_owner->task->pi_lock);
 		} else
 			set_new_owner(lock, old_owner, ti __EIP__);
-		__raw_spin_unlock(&lock->wait_lock);
-		__raw_spin_unlock(&task->pi_lock);
 		ret = 1;
 	}
 	__raw_spin_unlock(&lock->wait_lock);