[PATCH 2/2] lockdep reentrancy

[Mathieu Desnoyers]

Here is a patch to lockdep.c so it behaves correctly when a kprobe breakpoint is
put on a marker within hardirq tracing functions as long as the marker is within
the lockdep_recursion incremented boundaries. It should apply on 
2.6.20-rc4-git3.

Mathieu

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>


@@ -1841,33 +1843,36 @@ void trace_hardirqs_on(void)
 	struct task_struct *curr = current;
 	unsigned long ip;
 
 	if (unlikely(!debug_locks || current->lockdep_recursion))
 		return;
 
+	current->lockdep_recursion++;
+	barrier();
+
 	if (DEBUG_LOCKS_WARN_ON(unlikely(!early_boot_irqs_enabled)))
-		return;
+		goto end;
 
 	if (unlikely(curr->hardirqs_enabled)) {
 		debug_atomic_inc(&redundant_hardirqs_on);
-		return;
+		goto end;
 	}
 	/* we'll do an OFF -> ON transition: */
 	curr->hardirqs_enabled = 1;
 	ip = (unsigned long) __builtin_return_address(0);
 
 	if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
-		return;
+		goto end;
 	if (DEBUG_LOCKS_WARN_ON(current->hardirq_context))
-		return;
+		goto end;
 	/*
 	 * We are going to turn hardirqs on, so set the
 	 * usage bit for all held locks:
 	 */
 	if (!mark_held_locks(curr, 1, ip))
-		return;
+		goto end;
 	/*
 	 * If we have softirqs enabled, then set the usage
 	 * bit for all held locks. (disabled hardirqs prevented
@@ -1875,11 +1880,14 @@ void trace_hardirqs_on(void)
 	 */
 	if (curr->softirqs_enabled)
 		if (!mark_held_locks(curr, 0, ip))
-			return;
+			goto end;
 
 	curr->hardirq_enable_ip = ip;
 	curr->hardirq_enable_event = ++curr->irq_events;
 	debug_atomic_inc(&hardirqs_on_events);
+end:
+	barrier();
+	current->lockdep_recursion--;
 }
 
 EXPORT_SYMBOL(trace_hardirqs_on);
@@ -1888,14 +1896,17 @@ void trace_hardirqs_off(void)
 {
 	struct task_struct *curr = current;
 
 	if (unlikely(!debug_locks || current->lockdep_recursion))
 		return;
 
+	current->lockdep_recursion++;
+	barrier();
+	
 	if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
-		return;
+		goto end;
 
 	if (curr->hardirqs_enabled) {
 		/*
@@ -1910,6 +1921,9 @@ void trace_hardirqs_off(void)
 		debug_atomic_inc(&hardirqs_off_events);
 	} else
 		debug_atomic_inc(&redundant_hardirqs_off);
+end:
+	barrier();
+	current->lockdep_recursion--;
 }
 
 EXPORT_SYMBOL(trace_hardirqs_off);

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