[PATCH 2/2] locking: Apply contention tracepoints in the slow path

From: Namhyung Kim
Date: Wed Mar 16 2022 - 18:46:15 EST

Adding the lock contention tracepoints in various lock function slow
paths. Note that each arch can define spinlock differently, I only
added it only to the generic qspinlock for now.

Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
---
kernel/locking/mutex.c | 3 +++
kernel/locking/percpu-rwsem.c | 3 +++
kernel/locking/qrwlock.c | 9 +++++++++
kernel/locking/qspinlock.c | 5 +++++
kernel/locking/rtmutex.c | 11 +++++++++++
kernel/locking/rwbase_rt.c | 3 +++
kernel/locking/rwsem.c | 9 +++++++++
kernel/locking/semaphore.c | 14 +++++++++++++-
8 files changed, 56 insertions(+), 1 deletion(-)

diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index ee2fd7614a93..c88deda77cf2 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -644,6 +644,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
}

set_current_state(state);
+ trace_contention_begin(lock, 0);
for (;;) {
bool first;

@@ -710,6 +711,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
skip_wait:
/* got the lock - cleanup and rejoice! */
lock_acquired(&lock->dep_map, ip);
+ trace_contention_end(lock, 0);

if (ww_ctx)
ww_mutex_lock_acquired(ww, ww_ctx);
@@ -721,6 +723,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
err:
__set_current_state(TASK_RUNNING);
__mutex_remove_waiter(lock, &waiter);
+ trace_contention_end(lock, ret);
err_early_kill:
raw_spin_unlock(&lock->wait_lock);
debug_mutex_free_waiter(&waiter);
diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c
index c9fdae94e098..833043613af6 100644
--- a/kernel/locking/percpu-rwsem.c
+++ b/kernel/locking/percpu-rwsem.c
@@ -9,6 +9,7 @@
#include <linux/sched/task.h>
#include <linux/sched/debug.h>
#include <linux/errno.h>
+#include <trace/events/lock.h>

int __percpu_init_rwsem(struct percpu_rw_semaphore *sem,
const char *name, struct lock_class_key *key)
@@ -154,6 +155,7 @@ static void percpu_rwsem_wait(struct percpu_rw_semaphore *sem, bool reader)
}
spin_unlock_irq(&sem->waiters.lock);

+ trace_contention_begin(sem, LCB_F_PERCPU | (reader ? LCB_F_READ : LCB_F_WRITE));
while (wait) {
set_current_state(TASK_UNINTERRUPTIBLE);
if (!smp_load_acquire(&wq_entry.private))
@@ -161,6 +163,7 @@ static void percpu_rwsem_wait(struct percpu_rw_semaphore *sem, bool reader)
schedule();
}
__set_current_state(TASK_RUNNING);
+ trace_contention_end(sem, 0);
}

bool __sched __percpu_down_read(struct percpu_rw_semaphore *sem, bool try)
diff --git a/kernel/locking/qrwlock.c b/kernel/locking/qrwlock.c
index ec36b73f4733..b9f6f963d77f 100644
--- a/kernel/locking/qrwlock.c
+++ b/kernel/locking/qrwlock.c
@@ -12,6 +12,7 @@
#include <linux/percpu.h>
#include <linux/hardirq.h>
#include <linux/spinlock.h>
+#include <trace/events/lock.h>

/**
* queued_read_lock_slowpath - acquire read lock of a queue rwlock
@@ -34,6 +35,8 @@ void queued_read_lock_slowpath(struct qrwlock *lock)
}
atomic_sub(_QR_BIAS, &lock->cnts);

+ trace_contention_begin(lock, LCB_F_READ | LCB_F_SPIN);
+
/*
* Put the reader into the wait queue
*/
@@ -51,6 +54,8 @@ void queued_read_lock_slowpath(struct qrwlock *lock)
* Signal the next one in queue to become queue head
*/
arch_spin_unlock(&lock->wait_lock);
+
+ trace_contention_end(lock, 0);
}
EXPORT_SYMBOL(queued_read_lock_slowpath);

@@ -62,6 +67,8 @@ void queued_write_lock_slowpath(struct qrwlock *lock)
{
int cnts;

+ trace_contention_begin(lock, LCB_F_WRITE | LCB_F_SPIN);
+
/* Put the writer into the wait queue */
arch_spin_lock(&lock->wait_lock);

@@ -79,5 +86,7 @@ void queued_write_lock_slowpath(struct qrwlock *lock)
} while (!atomic_try_cmpxchg_acquire(&lock->cnts, &cnts, _QW_LOCKED));
unlock:
arch_spin_unlock(&lock->wait_lock);
+
+ trace_contention_end(lock, 0);
}
EXPORT_SYMBOL(queued_write_lock_slowpath);
diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
index cbff6ba53d56..65a9a10caa6f 100644
--- a/kernel/locking/qspinlock.c
+++ b/kernel/locking/qspinlock.c
@@ -22,6 +22,7 @@
#include <linux/prefetch.h>
#include <asm/byteorder.h>
#include <asm/qspinlock.h>
+#include <trace/events/lock.h>

/*
* Include queued spinlock statistics code
@@ -401,6 +402,8 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
idx = node->count++;
tail = encode_tail(smp_processor_id(), idx);

+ trace_contention_begin(lock, LCB_F_SPIN);
+
/*
* 4 nodes are allocated based on the assumption that there will
* not be nested NMIs taking spinlocks. That may not be true in
@@ -554,6 +557,8 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
pv_kick_node(lock, next);

release:
+ trace_contention_end(lock, 0);
+
/*
* release the node
*/
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 8555c4efe97c..7779ee8abc2a 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -24,6 +24,8 @@
#include <linux/sched/wake_q.h>
#include <linux/ww_mutex.h>

+#include <trace/events/lock.h>
+
#include "rtmutex_common.h"

#ifndef WW_RT
@@ -1579,6 +1581,8 @@ static int __sched __rt_mutex_slowlock(struct rt_mutex_base *lock,

set_current_state(state);

+ trace_contention_begin(lock, LCB_F_RT);
+
ret = task_blocks_on_rt_mutex(lock, waiter, current, ww_ctx, chwalk);
if (likely(!ret))
ret = rt_mutex_slowlock_block(lock, ww_ctx, state, NULL, waiter);
@@ -1601,6 +1605,9 @@ static int __sched __rt_mutex_slowlock(struct rt_mutex_base *lock,
* unconditionally. We might have to fix that up.
*/
fixup_rt_mutex_waiters(lock);
+
+ trace_contention_end(lock, ret);
+
return ret;
}

@@ -1683,6 +1690,8 @@ static void __sched rtlock_slowlock_locked(struct rt_mutex_base *lock)
/* Save current state and set state to TASK_RTLOCK_WAIT */
current_save_and_set_rtlock_wait_state();

+ trace_contention_begin(lock, LCB_F_RT);
+
task_blocks_on_rt_mutex(lock, &waiter, current, NULL, RT_MUTEX_MIN_CHAINWALK);

for (;;) {
@@ -1712,6 +1721,8 @@ static void __sched rtlock_slowlock_locked(struct rt_mutex_base *lock)
*/
fixup_rt_mutex_waiters(lock);
debug_rt_mutex_free_waiter(&waiter);
+
+ trace_contention_end(lock, 0);
}

static __always_inline void __sched rtlock_slowlock(struct rt_mutex_base *lock)
diff --git a/kernel/locking/rwbase_rt.c b/kernel/locking/rwbase_rt.c
index 6fd3162e4098..ec7b1fda7982 100644
--- a/kernel/locking/rwbase_rt.c
+++ b/kernel/locking/rwbase_rt.c
@@ -247,11 +247,13 @@ static int __sched rwbase_write_lock(struct rwbase_rt *rwb,
goto out_unlock;

rwbase_set_and_save_current_state(state);
+ trace_contention_begin(rwb, LCB_F_WRITE | LCB_F_RT);
for (;;) {
/* Optimized out for rwlocks */
if (rwbase_signal_pending_state(state, current)) {
rwbase_restore_current_state();
__rwbase_write_unlock(rwb, 0, flags);
+ trace_contention_end(rwb, -EINTR);
return -EINTR;
}

@@ -265,6 +267,7 @@ static int __sched rwbase_write_lock(struct rwbase_rt *rwb,
set_current_state(state);
}
rwbase_restore_current_state();
+ trace_contention_end(rwb, 0);

out_unlock:
raw_spin_unlock_irqrestore(&rtm->wait_lock, flags);
diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index acde5d6f1254..465db7bd84f8 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -27,6 +27,7 @@
#include <linux/export.h>
#include <linux/rwsem.h>
#include <linux/atomic.h>
+#include <trace/events/lock.h>

#ifndef CONFIG_PREEMPT_RT
#include "lock_events.h"
@@ -1014,6 +1015,8 @@ rwsem_down_read_slowpath(struct rw_semaphore *sem, long count, unsigned int stat
raw_spin_unlock_irq(&sem->wait_lock);
wake_up_q(&wake_q);

+ trace_contention_begin(sem, LCB_F_READ);
+
/* wait to be given the lock */
for (;;) {
set_current_state(state);
@@ -1035,6 +1038,7 @@ rwsem_down_read_slowpath(struct rw_semaphore *sem, long count, unsigned int stat

__set_current_state(TASK_RUNNING);
lockevent_inc(rwsem_rlock);
+ trace_contention_end(sem, 0);
return sem;

out_nolock:
@@ -1042,6 +1046,7 @@ rwsem_down_read_slowpath(struct rw_semaphore *sem, long count, unsigned int stat
raw_spin_unlock_irq(&sem->wait_lock);
__set_current_state(TASK_RUNNING);
lockevent_inc(rwsem_rlock_fail);
+ trace_contention_end(sem, -EINTR);
return ERR_PTR(-EINTR);
}

@@ -1109,6 +1114,8 @@ rwsem_down_write_slowpath(struct rw_semaphore *sem, int state)
wait:
/* wait until we successfully acquire the lock */
set_current_state(state);
+ trace_contention_begin(sem, LCB_F_WRITE);
+
for (;;) {
if (rwsem_try_write_lock(sem, &waiter)) {
/* rwsem_try_write_lock() implies ACQUIRE on success */
@@ -1148,6 +1155,7 @@ rwsem_down_write_slowpath(struct rw_semaphore *sem, int state)
__set_current_state(TASK_RUNNING);
raw_spin_unlock_irq(&sem->wait_lock);
lockevent_inc(rwsem_wlock);
+ trace_contention_end(sem, 0);
return sem;

out_nolock:
@@ -1159,6 +1167,7 @@ rwsem_down_write_slowpath(struct rw_semaphore *sem, int state)
raw_spin_unlock_irq(&sem->wait_lock);
wake_up_q(&wake_q);
lockevent_inc(rwsem_wlock_fail);
+ trace_contention_end(sem, -EINTR);
return ERR_PTR(-EINTR);
}

diff --git a/kernel/locking/semaphore.c b/kernel/locking/semaphore.c
index 9ee381e4d2a4..e3c19668dfee 100644
--- a/kernel/locking/semaphore.c
+++ b/kernel/locking/semaphore.c
@@ -32,6 +32,7 @@
#include <linux/semaphore.h>
#include <linux/spinlock.h>
#include <linux/ftrace.h>
+#include <trace/events/lock.h>

static noinline void __down(struct semaphore *sem);
static noinline int __down_interruptible(struct semaphore *sem);
@@ -209,6 +210,7 @@ static inline int __sched __down_common(struct semaphore *sem, long state,
long timeout)
{
struct semaphore_waiter waiter;
+ bool tracing = false;

list_add_tail(&waiter.list, &sem->wait_list);
waiter.task = current;
@@ -220,18 +222,28 @@ static inline int __sched __down_common(struct semaphore *sem, long state,
if (unlikely(timeout <= 0))
goto timed_out;
__set_current_state(state);
+ if (!tracing) {
+ trace_contention_begin(sem, 0);
+ tracing = true;
+ }
raw_spin_unlock_irq(&sem->lock);
timeout = schedule_timeout(timeout);
raw_spin_lock_irq(&sem->lock);
- if (waiter.up)
+ if (waiter.up) {
+ trace_contention_end(sem, 0);
return 0;
+ }
}

timed_out:
+ if (tracing)
+ trace_contention_end(sem, -ETIME);
list_del(&waiter.list);
return -ETIME;

interrupted:
+ if (tracing)
+ trace_contention_end(sem, -EINTR);
list_del(&waiter.list);
return -EINTR;
}
--
2.35.1.894.gb6a874cedc-goog