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

From: Peter Zijlstra
Date: Fri Aug 07 2020 - 15:34:43 EST


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@xxxxxxxxxxxxx>
---
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);