[PATCH 4/5] tracing/lock: Use TRACE_EVENT_FN() for contended_release

[Dmitry Ilvokhin <d@ilvokhin.com>]

queued_spin_unlock() gates its contended_release trace call behind a
static branch, so a NOP sits on the unlock path even while the
tracepoint is disabled. Removing that requires replacing the unlock
implementation only while contended_release is enabled, which needs a
callback when the tracepoint is toggled.

Convert contended_release to TRACE_EVENT_FN() and add weak no-op
arch_contended_release_trace_reg()/arch_contended_release_trace_unreg()
hooks.

The default hooks are empty, so this is a no-op until an architecture
overrides them.

No functional change intended.

Signed-off-by: Dmitry Ilvokhin <d@ilvokhin.com>
---
 include/trace/events/lock.h | 10 ++++++++--
 kernel/locking/mutex.c      |  4 ++++
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/include/trace/events/lock.h b/include/trace/events/lock.h
index 1ded869cd619..b1d5b18c4514 100644
--- a/include/trace/events/lock.h
+++ b/include/trace/events/lock.h
@@ -137,7 +137,11 @@ TRACE_EVENT(contention_end,
 	TP_printk("%p (ret=%d)", __entry->lock_addr, __entry->ret)
 );
 
-TRACE_EVENT(contended_release,
+/* kernel/locking/mutex.c */
+int arch_contended_release_trace_reg(void);
+void arch_contended_release_trace_unreg(void);
+
+TRACE_EVENT_FN(contended_release,
 
 	TP_PROTO(void *lock),
 
@@ -151,7 +155,9 @@ TRACE_EVENT(contended_release,
 		__entry->lock_addr = lock;
 	),
 
-	TP_printk("%p", __entry->lock_addr)
+	TP_printk("%p", __entry->lock_addr),
+
+	arch_contended_release_trace_reg, arch_contended_release_trace_unreg
 );
 
 #endif /* _TRACE_LOCK_H */
diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index 8a85912d7ee6..942a939cee95 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -1272,6 +1272,10 @@ EXPORT_TRACEPOINT_SYMBOL_GPL(contention_begin);
 EXPORT_TRACEPOINT_SYMBOL_GPL(contention_end);
 EXPORT_TRACEPOINT_SYMBOL_GPL(contended_release);
 
+__weak int arch_contended_release_trace_reg(void) { return 0; }
+
+__weak void arch_contended_release_trace_unreg(void) { }
+
 /**
  * atomic_dec_and_mutex_lock - return holding mutex if we dec to 0
  * @cnt: the atomic which we are to dec
-- 
2.53.0-Meta