linux-kernel - [RFC][PATCH 3/3] lockdep,trace: Expose tracepoints

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Date:   Fri, 07 Aug 2020 21:23:39 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     tglx@...utronix.de, mingo@...nel.org, will@...nel.org
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, elver@...gle.com,
        paulmck@...nel.org, rostedt@...dmis.org, rjw@...ysocki.net,
        peterz@...radead.org
Subject: [RFC][PATCH 3/3] lockdep,trace: Expose tracepoints

The lockdep tracepoints are under the lockdep recursion counter, this
has a bunch of nasty side effects:

 - TRACE_IRQFLAGS doesn't work across the entire tracepoint, leading to
   all sorts of dodgy complaints.

 - RCU-lockdep doesn't see the tracepoints either, hiding numerous
   "suspicious RCU usage" warnings.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 kernel/locking/lockdep.c |   27 ++++++++++++++++++---------
 1 file changed, 18 insertions(+), 9 deletions(-)

--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -5000,8 +5000,9 @@ void lock_acquire(struct lockdep_map *lo
 	raw_local_irq_save(flags);
 	check_flags(flags);
 
-	current->lockdep_recursion++;
 	trace_lock_acquire(lock, subclass, trylock, read, check, nest_lock, ip);
+
+	current->lockdep_recursion++;
 	__lock_acquire(lock, subclass, trylock, read, check,
 		       irqs_disabled_flags(flags), nest_lock, ip, 0, 0);
 	lockdep_recursion_finish();
@@ -5016,10 +5017,13 @@ void lock_release(struct lockdep_map *lo
 	if (unlikely(current->lockdep_recursion))
 		return;
 
+
 	raw_local_irq_save(flags);
 	check_flags(flags);
-	current->lockdep_recursion++;
+
 	trace_lock_release(lock, ip);
+
+	current->lockdep_recursion++;
 	if (__lock_release(lock, ip))
 		check_chain_key(current);
 	lockdep_recursion_finish();
@@ -5171,7 +5175,7 @@ __lock_contended(struct lockdep_map *loc
 		stats->bounces[bounce_contended + !!hlock->read]++;
 }
 
-static void
+static bool
 __lock_acquired(struct lockdep_map *lock, unsigned long ip)
 {
 	struct task_struct *curr = current;
@@ -5187,16 +5191,16 @@ __lock_acquired(struct lockdep_map *lock
 	 * acquire, how the heck did that happen?
 	 */
 	if (DEBUG_LOCKS_WARN_ON(!depth))
-		return;
+		return false;
 
 	hlock = find_held_lock(curr, lock, depth, &i);
 	if (!hlock) {
 		print_lock_contention_bug(curr, lock, _RET_IP_);
-		return;
+		return false;
 	}
 
 	if (hlock->instance != lock)
-		return;
+		return false;
 
 	cpu = smp_processor_id();
 	if (hlock->waittime_stamp) {
@@ -5205,8 +5209,6 @@ __lock_acquired(struct lockdep_map *lock
 		hlock->holdtime_stamp = now;
 	}
 
-	trace_lock_acquired(lock, ip);
-
 	stats = get_lock_stats(hlock_class(hlock));
 	if (waittime) {
 		if (hlock->read)
@@ -5219,6 +5221,8 @@ __lock_acquired(struct lockdep_map *lock
 
 	lock->cpu = cpu;
 	lock->ip = ip;
+
+	return true;
 }
 
 void lock_contended(struct lockdep_map *lock, unsigned long ip)
@@ -5244,6 +5248,7 @@ EXPORT_SYMBOL_GPL(lock_contended);
 void lock_acquired(struct lockdep_map *lock, unsigned long ip)
 {
 	unsigned long flags;
+	bool trace;
 
 	if (unlikely(!lock_stat || !debug_locks))
 		return;
@@ -5254,8 +5259,12 @@ void lock_acquired(struct lockdep_map *l
 	raw_local_irq_save(flags);
 	check_flags(flags);
 	current->lockdep_recursion++;
-	__lock_acquired(lock, ip);
+	trace = __lock_acquired(lock, ip);
 	lockdep_recursion_finish();
+
+	if (trace)
+		trace_lock_acquired(lock, ip);
+
 	raw_local_irq_restore(flags);
 }
 EXPORT_SYMBOL_GPL(lock_acquired);