[PATCH v11 1/7] locking/mutex: Remove wakeups from under mutex::wait_lock

From: John Stultz
Date: Tue Jul 09 2024 - 16:32:44 EST

From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>

In preparation to nest mutex::wait_lock under rq::lock we need to remove
wakeups from under it.

Cc: Joel Fernandes <joelaf@xxxxxxxxxx>
Cc: Qais Yousef <qyousef@xxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Juri Lelli <juri.lelli@xxxxxxxxxx>
Cc: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Cc: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
Cc: Valentin Schneider <vschneid@xxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Ben Segall <bsegall@xxxxxxxxxx>
Cc: Zimuzo Ezeozue <zezeozue@xxxxxxxxxx>
Cc: Youssef Esmat <youssefesmat@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Waiman Long <longman@xxxxxxxxxx>
Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
Cc: Metin Kaya <Metin.Kaya@xxxxxxx>
Cc: Xuewen Yan <xuewen.yan94@xxxxxxxxx>
Cc: K Prateek Nayak <kprateek.nayak@xxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
Cc: kernel-team@xxxxxxxxxxx
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
[Heavily changed after 55f036ca7e74 ("locking: WW mutex cleanup") and
08295b3b5bee ("locking: Implement an algorithm choice for Wound-Wait
mutexes")]
Signed-off-by: Juri Lelli <juri.lelli@xxxxxxxxxx>
[jstultz: rebased to mainline, added extra wake_up_q & init
to avoid hangs, similar to Connor's rework of this patch]
Signed-off-by: John Stultz <jstultz@xxxxxxxxxx>
Tested-by: K Prateek Nayak <kprateek.nayak@xxxxxxx>
Tested-by: Metin Kaya <metin.kaya@xxxxxxx>
Acked-by: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Reviewed-by: Metin Kaya <metin.kaya@xxxxxxx>
---
v5:
* Reverted back to an earlier version of this patch to undo
the change that kept the wake_q in the ctx structure, as
that broke the rule that the wake_q must always be on the
stack, as its not safe for concurrency.
v6:
* Made tweaks suggested by Waiman Long
v7:
* Fixups to pass wake_qs down for PREEMPT_RT logic
v10:
* Switched preempt_enable to be lower close to the unlock as
suggested by Valentin
* Added additional preempt_disable coverage around the wake_q
calls as again noted by Valentin
---
kernel/locking/mutex.c | 17 +++++++++++++----
kernel/locking/rtmutex.c | 30 +++++++++++++++++++++---------
kernel/locking/rwbase_rt.c | 8 +++++++-
kernel/locking/rwsem.c | 4 ++--
kernel/locking/spinlock_rt.c | 3 ++-
kernel/locking/ww_mutex.h | 29 ++++++++++++++++++-----------
6 files changed, 63 insertions(+), 28 deletions(-)

diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index cbae8c0b89ab..4269da1f3ef5 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -575,6 +575,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
struct lockdep_map *nest_lock, unsigned long ip,
struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx)
{
+ DEFINE_WAKE_Q(wake_q);
struct mutex_waiter waiter;
struct ww_mutex *ww;
int ret;
@@ -625,7 +626,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
*/
if (__mutex_trylock(lock)) {
if (ww_ctx)
- __ww_mutex_check_waiters(lock, ww_ctx);
+ __ww_mutex_check_waiters(lock, ww_ctx, &wake_q);

goto skip_wait;
}
@@ -645,7 +646,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
* Add in stamp order, waking up waiters that must kill
* themselves.
*/
- ret = __ww_mutex_add_waiter(&waiter, lock, ww_ctx);
+ ret = __ww_mutex_add_waiter(&waiter, lock, ww_ctx, &wake_q);
if (ret)
goto err_early_kill;
}
@@ -681,6 +682,11 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
}

raw_spin_unlock(&lock->wait_lock);
+ /* Make sure we do wakeups before calling schedule */
+ if (!wake_q_empty(&wake_q)) {
+ wake_up_q(&wake_q);
+ wake_q_init(&wake_q);
+ }
schedule_preempt_disabled();

first = __mutex_waiter_is_first(lock, &waiter);
@@ -714,7 +720,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
*/
if (!ww_ctx->is_wait_die &&
!__mutex_waiter_is_first(lock, &waiter))
- __ww_mutex_check_waiters(lock, ww_ctx);
+ __ww_mutex_check_waiters(lock, ww_ctx, &wake_q);
}

__mutex_remove_waiter(lock, &waiter);
@@ -730,6 +736,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
ww_mutex_lock_acquired(ww, ww_ctx);

raw_spin_unlock(&lock->wait_lock);
+ wake_up_q(&wake_q);
preempt_enable();
return 0;

@@ -741,6 +748,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
raw_spin_unlock(&lock->wait_lock);
debug_mutex_free_waiter(&waiter);
mutex_release(&lock->dep_map, ip);
+ wake_up_q(&wake_q);
preempt_enable();
return ret;
}
@@ -951,9 +959,10 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
if (owner & MUTEX_FLAG_HANDOFF)
__mutex_handoff(lock, next);

+ preempt_disable();
raw_spin_unlock(&lock->wait_lock);
-
wake_up_q(&wake_q);
+ preempt_enable();
}

#ifndef CONFIG_DEBUG_LOCK_ALLOC
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 88d08eeb8bc0..7a85d9bfa972 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -34,13 +34,15 @@

static inline int __ww_mutex_add_waiter(struct rt_mutex_waiter *waiter,
struct rt_mutex *lock,
- struct ww_acquire_ctx *ww_ctx)
+ struct ww_acquire_ctx *ww_ctx,
+ struct wake_q_head *wake_q)
{
return 0;
}

static inline void __ww_mutex_check_waiters(struct rt_mutex *lock,
- struct ww_acquire_ctx *ww_ctx)
+ struct ww_acquire_ctx *ww_ctx,
+ struct wake_q_head *wake_q)
{
}

@@ -1207,6 +1209,7 @@ static int __sched task_blocks_on_rt_mutex(struct rt_mutex_base *lock,
struct rt_mutex_waiter *top_waiter = waiter;
struct rt_mutex_base *next_lock;
int chain_walk = 0, res;
+ DEFINE_WAKE_Q(wake_q);

lockdep_assert_held(&lock->wait_lock);

@@ -1245,7 +1248,10 @@ static int __sched task_blocks_on_rt_mutex(struct rt_mutex_base *lock,

/* Check whether the waiter should back out immediately */
rtm = container_of(lock, struct rt_mutex, rtmutex);
- res = __ww_mutex_add_waiter(waiter, rtm, ww_ctx);
+ preempt_disable();
+ res = __ww_mutex_add_waiter(waiter, rtm, ww_ctx, &wake_q);
+ wake_up_q(&wake_q);
+ preempt_enable();
if (res) {
raw_spin_lock(&task->pi_lock);
rt_mutex_dequeue(lock, waiter);
@@ -1678,7 +1684,8 @@ static int __sched __rt_mutex_slowlock(struct rt_mutex_base *lock,
struct ww_acquire_ctx *ww_ctx,
unsigned int state,
enum rtmutex_chainwalk chwalk,
- struct rt_mutex_waiter *waiter)
+ struct rt_mutex_waiter *waiter,
+ struct wake_q_head *wake_q)
{
struct rt_mutex *rtm = container_of(lock, struct rt_mutex, rtmutex);
struct ww_mutex *ww = ww_container_of(rtm);
@@ -1689,7 +1696,7 @@ static int __sched __rt_mutex_slowlock(struct rt_mutex_base *lock,
/* Try to acquire the lock again: */
if (try_to_take_rt_mutex(lock, current, NULL)) {
if (build_ww_mutex() && ww_ctx) {
- __ww_mutex_check_waiters(rtm, ww_ctx);
+ __ww_mutex_check_waiters(rtm, ww_ctx, wake_q);
ww_mutex_lock_acquired(ww, ww_ctx);
}
return 0;
@@ -1707,7 +1714,7 @@ static int __sched __rt_mutex_slowlock(struct rt_mutex_base *lock,
/* acquired the lock */
if (build_ww_mutex() && ww_ctx) {
if (!ww_ctx->is_wait_die)
- __ww_mutex_check_waiters(rtm, ww_ctx);
+ __ww_mutex_check_waiters(rtm, ww_ctx, wake_q);
ww_mutex_lock_acquired(ww, ww_ctx);
}
} else {
@@ -1729,7 +1736,8 @@ static int __sched __rt_mutex_slowlock(struct rt_mutex_base *lock,

static inline int __rt_mutex_slowlock_locked(struct rt_mutex_base *lock,
struct ww_acquire_ctx *ww_ctx,
- unsigned int state)
+ unsigned int state,
+ struct wake_q_head *wake_q)
{
struct rt_mutex_waiter waiter;
int ret;
@@ -1738,7 +1746,7 @@ static inline int __rt_mutex_slowlock_locked(struct rt_mutex_base *lock,
waiter.ww_ctx = ww_ctx;

ret = __rt_mutex_slowlock(lock, ww_ctx, state, RT_MUTEX_MIN_CHAINWALK,
- &waiter);
+ &waiter, wake_q);

debug_rt_mutex_free_waiter(&waiter);
return ret;
@@ -1754,6 +1762,7 @@ static int __sched rt_mutex_slowlock(struct rt_mutex_base *lock,
struct ww_acquire_ctx *ww_ctx,
unsigned int state)
{
+ DEFINE_WAKE_Q(wake_q);
unsigned long flags;
int ret;

@@ -1775,8 +1784,11 @@ static int __sched rt_mutex_slowlock(struct rt_mutex_base *lock,
* irqsave/restore variants.
*/
raw_spin_lock_irqsave(&lock->wait_lock, flags);
- ret = __rt_mutex_slowlock_locked(lock, ww_ctx, state);
+ ret = __rt_mutex_slowlock_locked(lock, ww_ctx, state, &wake_q);
+ preempt_disable();
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
+ wake_up_q(&wake_q);
+ preempt_enable();
rt_mutex_post_schedule();

return ret;
diff --git a/kernel/locking/rwbase_rt.c b/kernel/locking/rwbase_rt.c
index 34a59569db6b..9f4322c07486 100644
--- a/kernel/locking/rwbase_rt.c
+++ b/kernel/locking/rwbase_rt.c
@@ -69,6 +69,7 @@ static int __sched __rwbase_read_lock(struct rwbase_rt *rwb,
unsigned int state)
{
struct rt_mutex_base *rtm = &rwb->rtmutex;
+ DEFINE_WAKE_Q(wake_q);
int ret;

rwbase_pre_schedule();
@@ -110,7 +111,7 @@ static int __sched __rwbase_read_lock(struct rwbase_rt *rwb,
* For rwlocks this returns 0 unconditionally, so the below
* !ret conditionals are optimized out.
*/
- ret = rwbase_rtmutex_slowlock_locked(rtm, state);
+ ret = rwbase_rtmutex_slowlock_locked(rtm, state, &wake_q);

/*
* On success the rtmutex is held, so there can't be a writer
@@ -121,7 +122,12 @@ static int __sched __rwbase_read_lock(struct rwbase_rt *rwb,
*/
if (!ret)
atomic_inc(&rwb->readers);
+
+ preempt_disable();
raw_spin_unlock_irq(&rtm->wait_lock);
+ wake_up_q(&wake_q);
+ preempt_enable();
+
if (!ret)
rwbase_rtmutex_unlock(rtm);

diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index c6d17aee4209..79ab7b8df5c1 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -1415,8 +1415,8 @@ static inline void __downgrade_write(struct rw_semaphore *sem)
#define rwbase_rtmutex_lock_state(rtm, state) \
__rt_mutex_lock(rtm, state)

-#define rwbase_rtmutex_slowlock_locked(rtm, state) \
- __rt_mutex_slowlock_locked(rtm, NULL, state)
+#define rwbase_rtmutex_slowlock_locked(rtm, state, wq) \
+ __rt_mutex_slowlock_locked(rtm, NULL, state, wq)

#define rwbase_rtmutex_unlock(rtm) \
__rt_mutex_unlock(rtm)
diff --git a/kernel/locking/spinlock_rt.c b/kernel/locking/spinlock_rt.c
index 38e292454fcc..fb1810a14c9d 100644
--- a/kernel/locking/spinlock_rt.c
+++ b/kernel/locking/spinlock_rt.c
@@ -162,7 +162,8 @@ rwbase_rtmutex_lock_state(struct rt_mutex_base *rtm, unsigned int state)
}

static __always_inline int
-rwbase_rtmutex_slowlock_locked(struct rt_mutex_base *rtm, unsigned int state)
+rwbase_rtmutex_slowlock_locked(struct rt_mutex_base *rtm, unsigned int state,
+ struct wake_q_head *wake_q)
{
rtlock_slowlock_locked(rtm);
return 0;
diff --git a/kernel/locking/ww_mutex.h b/kernel/locking/ww_mutex.h
index 3ad2cc4823e5..7189c6631d90 100644
--- a/kernel/locking/ww_mutex.h
+++ b/kernel/locking/ww_mutex.h
@@ -275,7 +275,7 @@ __ww_ctx_less(struct ww_acquire_ctx *a, struct ww_acquire_ctx *b)
*/
static bool
__ww_mutex_die(struct MUTEX *lock, struct MUTEX_WAITER *waiter,
- struct ww_acquire_ctx *ww_ctx)
+ struct ww_acquire_ctx *ww_ctx, struct wake_q_head *wake_q)
{
if (!ww_ctx->is_wait_die)
return false;
@@ -284,7 +284,7 @@ __ww_mutex_die(struct MUTEX *lock, struct MUTEX_WAITER *waiter,
#ifndef WW_RT
debug_mutex_wake_waiter(lock, waiter);
#endif
- wake_up_process(waiter->task);
+ wake_q_add(wake_q, waiter->task);
}

return true;
@@ -299,7 +299,8 @@ __ww_mutex_die(struct MUTEX *lock, struct MUTEX_WAITER *waiter,
*/
static bool __ww_mutex_wound(struct MUTEX *lock,
struct ww_acquire_ctx *ww_ctx,
- struct ww_acquire_ctx *hold_ctx)
+ struct ww_acquire_ctx *hold_ctx,
+ struct wake_q_head *wake_q)
{
struct task_struct *owner = __ww_mutex_owner(lock);

@@ -331,7 +332,7 @@ static bool __ww_mutex_wound(struct MUTEX *lock,
* wakeup pending to re-read the wounded state.
*/
if (owner != current)
- wake_up_process(owner);
+ wake_q_add(wake_q, owner);

return true;
}
@@ -352,7 +353,8 @@ static bool __ww_mutex_wound(struct MUTEX *lock,
* The current task must not be on the wait list.
*/
static void
-__ww_mutex_check_waiters(struct MUTEX *lock, struct ww_acquire_ctx *ww_ctx)
+__ww_mutex_check_waiters(struct MUTEX *lock, struct ww_acquire_ctx *ww_ctx,
+ struct wake_q_head *wake_q)
{
struct MUTEX_WAITER *cur;

@@ -364,8 +366,8 @@ __ww_mutex_check_waiters(struct MUTEX *lock, struct ww_acquire_ctx *ww_ctx)
if (!cur->ww_ctx)
continue;

- if (__ww_mutex_die(lock, cur, ww_ctx) ||
- __ww_mutex_wound(lock, cur->ww_ctx, ww_ctx))
+ if (__ww_mutex_die(lock, cur, ww_ctx, wake_q) ||
+ __ww_mutex_wound(lock, cur->ww_ctx, ww_ctx, wake_q))
break;
}
}
@@ -377,6 +379,8 @@ __ww_mutex_check_waiters(struct MUTEX *lock, struct ww_acquire_ctx *ww_ctx)
static __always_inline void
ww_mutex_set_context_fastpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
{
+ DEFINE_WAKE_Q(wake_q);
+
ww_mutex_lock_acquired(lock, ctx);

/*
@@ -405,8 +409,10 @@ ww_mutex_set_context_fastpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
* die or wound us.
*/
lock_wait_lock(&lock->base);
- __ww_mutex_check_waiters(&lock->base, ctx);
+ __ww_mutex_check_waiters(&lock->base, ctx, &wake_q);
unlock_wait_lock(&lock->base);
+
+ wake_up_q(&wake_q);
}

static __always_inline int
@@ -488,7 +494,8 @@ __ww_mutex_check_kill(struct MUTEX *lock, struct MUTEX_WAITER *waiter,
static inline int
__ww_mutex_add_waiter(struct MUTEX_WAITER *waiter,
struct MUTEX *lock,
- struct ww_acquire_ctx *ww_ctx)
+ struct ww_acquire_ctx *ww_ctx,
+ struct wake_q_head *wake_q)
{
struct MUTEX_WAITER *cur, *pos = NULL;
bool is_wait_die;
@@ -532,7 +539,7 @@ __ww_mutex_add_waiter(struct MUTEX_WAITER *waiter,
pos = cur;

/* Wait-Die: ensure younger waiters die. */
- __ww_mutex_die(lock, cur, ww_ctx);
+ __ww_mutex_die(lock, cur, ww_ctx, wake_q);
}

__ww_waiter_add(lock, waiter, pos);
@@ -550,7 +557,7 @@ __ww_mutex_add_waiter(struct MUTEX_WAITER *waiter,
* such that either we or the fastpath will wound @ww->ctx.
*/
smp_mb();
- __ww_mutex_wound(lock, ww_ctx, ww->ctx);
+ __ww_mutex_wound(lock, ww_ctx, ww->ctx, wake_q);
}

return 0;
--
2.45.2.993.g49e7a77208-goog