[PATCH] robust pi futex tracing

[Darren Hart]

---
 kernel/futex.c |   24 ++++++++++++++++++++----
 1 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index e7a35f1..24ac437 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -683,6 +683,8 @@ retry:
 	 */
 	if (unlikely(ownerdied || !(curval & FUTEX_TID_MASK))) {
 		/* Keep the OWNER_DIED bit */
+		if (ownerdied)
+			trace_printk("ownerdied, taking over lock\n");
 		newval = (curval & ~FUTEX_TID_MASK) | task_pid_vnr(task);
 		ownerdied = 0;
 		lock_taken = 1;
@@ -692,14 +694,18 @@ retry:
 
 	if (unlikely(curval == -EFAULT))
 		return -EFAULT;
-	if (unlikely(curval != uval))
+	if (unlikely(curval != uval)) {
+		trace_printk("cmpxchg failed, retrying\n");
 		goto retry;
+	}
 
 	/*
 	 * We took the lock due to owner died take over.
 	 */
-	if (unlikely(lock_taken))
+	if (unlikely(lock_taken)) {
+		trace_printk("ownerdied, lock acquired, return 1\n");
 		return 1;
+	}
 
 	/*
 	 * We dont have the lock. Look up the PI state (or create it if
@@ -710,13 +716,16 @@ retry:
 	if (unlikely(ret)) {
 		switch (ret) {
 		case -ESRCH:
+			trace_printk("lookup_pi_state: -ESRCH\n");
 			/*
 			 * No owner found for this futex. Check if the
 			 * OWNER_DIED bit is set to figure out whether
 			 * this is a robust futex or not.
 			 */
-			if (get_futex_value_locked(&curval, uaddr))
+			if (get_futex_value_locked(&curval, uaddr)) {
+				trace_printk("get_futex_value_locked: -EFAULT\n");
 				return -EFAULT;
+			}
 
 			/*
 			 * We simply start over in case of a robust
@@ -724,10 +733,13 @@ retry:
 			 * and return happy.
 			 */
 			if (curval & FUTEX_OWNER_DIED) {
+				trace_printk("ownerdied, goto retry\n");
 				ownerdied = 1;
 				goto retry;
 			}
+			trace_printk("ownerdied not detected, returning -ESRCH\n");
 		default:
+			trace_printk("lookup_pi_state: %d\n", ret);
 			break;
 		}
 	}
@@ -1950,6 +1962,8 @@ retry_private:
 			put_futex_key(fshared, &q.key);
 			cond_resched();
 			goto retry;
+		case -ESRCH:
+			trace_printk("returning -ESRCH to userspace\n");
 		default:
 			goto out_unlock_put_key;
 		}
@@ -2537,8 +2551,10 @@ void exit_robust_list(struct task_struct *curr)
 		/*
 		 * Avoid excessively long or circular lists:
 		 */
-		if (!--limit)
+		if (!--limit) {
+			trace_printk("excessively long list, aborting\n");
 			break;
+		}
 
 		cond_resched();
 	}
-- 
1.7.0.4

-- 
Darren Hart
IBM Linux Technology Center
Real-Time Linux Team
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