[PATCH 1/4] locking: Add lock contention tracepoints

Namhyung Kim
2022-03-01T01:04:31Z

This adds two new lock contention tracepoints like below:

* lock:contention_begin
* lock:contention_end

The lock:contention_begin takes a flags argument to classify locks. I
found it useful to pass a task state it goes to and it can tell if the
given lock is busy-waiting (spinlock) or sleeping (mutex or semaphore).
Also it has info whether it's a reader-writer lock, real-time, and
per-cpu.

Move tracepoint definitions into a separate file so that we can use
some of them without lockdep. Also lock_trace.h header was added to
provide access to the tracepoints in the header file (like spinlock.h)
which cannot include the tracepoint definition directly.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
include/linux/lock_trace.h | 31 +++++++++++++++++++++++++++
include/trace/events/lock.h | 42 ++++++++++++++++++++++++++++++++++++-
kernel/locking/Makefile | 2 +-
kernel/locking/lockdep.c | 1 -
kernel/locking/tracepoint.c | 21 +++++++++++++++++++
5 files changed, 94 insertions(+), 3 deletions(-)
create mode 100644 include/linux/lock_trace.h
create mode 100644 kernel/locking/tracepoint.c

diff --git a/include/linux/lock_trace.h b/include/linux/lock_trace.h
new file mode 100644
index 000000000000..d84bcc9570a4
--- /dev/null
+++ b/include/linux/lock_trace.h
@@ -0,0 +1,31 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef __LINUX_LOCK_TRACE_H
+#define __LINUX_LOCK_TRACE_H
+
+#include <linux/tracepoint-defs.h>
+
+DECLARE_TRACEPOINT(contention_begin);
+DECLARE_TRACEPOINT(contention_end);
+
+#define LCB_F_READ (1U << 31)
+#define LCB_F_WRITE (1U << 30)
+#define LCB_F_RT (1U << 29)
+#define LCB_F_PERCPU (1U << 28)
+
+extern void lock_contention_begin(void *lock, unsigned long ip,
+ unsigned int flags);
+extern void lock_contention_end(void *lock);
+
+#define LOCK_CONTENTION_BEGIN(_lock, _flags) \
+ do { \
+ if (tracepoint_enabled(contention_begin)) \
+ lock_contention_begin(_lock, _RET_IP_, _flags); \
+ } while (0)
+
+#define LOCK_CONTENTION_END(_lock) \
+ do { \
+ if (tracepoint_enabled(contention_end)) \
+ lock_contention_end(_lock); \
+ } while (0)
+
+#endif /* __LINUX_LOCK_TRACE_H */
diff --git a/include/trace/events/lock.h b/include/trace/events/lock.h
index d7512129a324..7bca0a537dbd 100644
--- a/include/trace/events/lock.h
+++ b/include/trace/events/lock.h
@@ -5,11 +5,12 @@
#if !defined(_TRACE_LOCK_H) || defined(TRACE_HEADER_MULTI_READ)
#define _TRACE_LOCK_H

-#include <linux/lockdep.h>
#include <linux/tracepoint.h>

#ifdef CONFIG_LOCKDEP

+#include <linux/lockdep.h>
+
TRACE_EVENT(lock_acquire,

TP_PROTO(struct lockdep_map *lock, unsigned int subclass,
@@ -81,6 +82,45 @@ DEFINE_EVENT(lock, lock_acquired,
#endif
#endif

+TRACE_EVENT(contention_begin,
+
+ TP_PROTO(void *lock, unsigned long ip, unsigned int flags),
+
+ TP_ARGS(lock, ip, flags),
+
+ TP_STRUCT__entry(
+ __field(void *, lock_addr)
+ __field(unsigned long, ip)
+ __field(unsigned int, flags)
+ ),
+
+ TP_fast_assign(
+ __entry->lock_addr = lock;
+ __entry->ip = ip;
+ __entry->flags = flags;
+ ),
+
+ TP_printk("%p %pS (%x)", __entry->lock_addr, (void *) __entry->ip,
+ __entry->flags)
+);
+
+TRACE_EVENT(contention_end,
+
+ TP_PROTO(void *lock),
+
+ TP_ARGS(lock),
+
+ TP_STRUCT__entry(
+ __field(void *, lock_addr)
+ ),
+
+ TP_fast_assign(
+ __entry->lock_addr = lock;
+ ),
+
+ TP_printk("%p", __entry->lock_addr)
+);
+
#endif /* _TRACE_LOCK_H */

/* This part must be outside protection */
diff --git a/kernel/locking/Makefile b/kernel/locking/Makefile
index d51cabf28f38..d212401adcdc 100644
--- a/kernel/locking/Makefile
+++ b/kernel/locking/Makefile
@@ -3,7 +3,7 @@
# and is generally not a function of system call inputs.
KCOV_INSTRUMENT := n

-obj-y += mutex.o semaphore.o rwsem.o percpu-rwsem.o
+obj-y += mutex.o semaphore.o rwsem.o percpu-rwsem.o tracepoint.o

# Avoid recursion lockdep -> KCSAN -> ... -> lockdep.
KCSAN_SANITIZE_lockdep.o := n
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 50036c10b518..08f8fb6a2d1e 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -60,7 +60,6 @@

#include "lockdep_internals.h"

-#define CREATE_TRACE_POINTS
#include <trace/events/lock.h>

#ifdef CONFIG_PROVE_LOCKING
diff --git a/kernel/locking/tracepoint.c b/kernel/locking/tracepoint.c
new file mode 100644
index 000000000000..d6f5c6c1d7bd
--- /dev/null
+++ b/kernel/locking/tracepoint.c
@@ -0,0 +1,21 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#include <linux/lock_trace.h>
+
+#define CREATE_TRACE_POINTS
+#include <trace/events/lock.h>
+
+/* these are exported via LOCK_CONTENTION_{BEGIN,END} macro */
+EXPORT_TRACEPOINT_SYMBOL_GPL(contention_begin);
+EXPORT_TRACEPOINT_SYMBOL_GPL(contention_end);
+
+void lock_contention_begin(void *lock, unsigned long ip, unsigned int flags)
+{
+ trace_contention_begin(lock, ip, flags);
+}
+EXPORT_SYMBOL_GPL(lock_contention_begin);
+
+void lock_contention_end(void *lock)
+{
+ trace_contention_end(lock);
+}
+EXPORT_SYMBOL_GPL(lock_contention_end);
--
2.35.1.574.g5d30c73bfb-goog