[RFC][PATCH v1.1 3/3] lockdep,trace: Expose tracepoints

From: peterz
Date: Mon Aug 10 2020 - 08:26:52 EST


Subject: lockdep,trace: Expose tracepoints
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Fri Aug 7 20:53:16 CEST 2020

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

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

Pull the trace_lock_*() tracepoints completely out from under the
lockdep recursion handling and completely rely on the trace level
recusion handling -- also, tracing *SHOULD* not be taking locks in any
case.

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
kernel/locking/lockdep.c | 14 +++++++++-----
1 file changed, 9 insertions(+), 5 deletions(-)

--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -4977,6 +4977,8 @@ void lock_acquire(struct lockdep_map *lo
{
unsigned long flags;

+ trace_lock_acquire(lock, subclass, trylock, read, check, nest_lock, ip);
+
if (unlikely(current->lockdep_recursion)) {
/* XXX allow trylock from NMI ?!? */
if (lockdep_nmi() && !trylock) {
@@ -5001,7 +5003,6 @@ void lock_acquire(struct lockdep_map *lo
check_flags(flags);

current->lockdep_recursion++;
- trace_lock_acquire(lock, subclass, trylock, read, check, nest_lock, ip);
__lock_acquire(lock, subclass, trylock, read, check,
irqs_disabled_flags(flags), nest_lock, ip, 0, 0);
lockdep_recursion_finish();
@@ -5013,13 +5014,15 @@ void lock_release(struct lockdep_map *lo
{
unsigned long flags;

+ trace_lock_release(lock, ip);
+
if (unlikely(current->lockdep_recursion))
return;

raw_local_irq_save(flags);
check_flags(flags);
+
current->lockdep_recursion++;
- trace_lock_release(lock, ip);
if (__lock_release(lock, ip))
check_chain_key(current);
lockdep_recursion_finish();
@@ -5205,8 +5208,6 @@ __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)
@@ -5225,6 +5226,8 @@ void lock_contended(struct lockdep_map *
{
unsigned long flags;

+ trace_lock_contended(lock, ip);
+
if (unlikely(!lock_stat || !debug_locks))
return;

@@ -5234,7 +5237,6 @@ void lock_contended(struct lockdep_map *
raw_local_irq_save(flags);
check_flags(flags);
current->lockdep_recursion++;
- trace_lock_contended(lock, ip);
__lock_contended(lock, ip);
lockdep_recursion_finish();
raw_local_irq_restore(flags);
@@ -5245,6 +5247,8 @@ void lock_acquired(struct lockdep_map *l
{
unsigned long flags;

+ trace_lock_acquired(lock, ip);
+
if (unlikely(!lock_stat || !debug_locks))
return;