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Subject[RFC PATCH 01/11] locking/ww_mutex: Remove wakeups from under mutex::wait_lock
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From: Peter Zijlstra <peterz@infradead.org>

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

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Connor O'Brien <connoro@google.com>
---
include/linux/ww_mutex.h | 3 +++
kernel/locking/mutex.c | 8 ++++++++
kernel/locking/ww_mutex.h | 9 +++++++--
kernel/sched/core.c | 7 +++++++
4 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/include/linux/ww_mutex.h b/include/linux/ww_mutex.h
index bb763085479a..9335b2202017 100644
--- a/include/linux/ww_mutex.h
+++ b/include/linux/ww_mutex.h
@@ -19,6 +19,7 @@

#include <linux/mutex.h>
#include <linux/rtmutex.h>
+#include <linux/sched/wake_q.h>

#if defined(CONFIG_DEBUG_MUTEXES) || \
(defined(CONFIG_PREEMPT_RT) && defined(CONFIG_DEBUG_RT_MUTEXES))
@@ -58,6 +59,7 @@ struct ww_acquire_ctx {
unsigned int acquired;
unsigned short wounded;
unsigned short is_wait_die;
+ struct wake_q_head wake_q;
#ifdef DEBUG_WW_MUTEXES
unsigned int done_acquire;
struct ww_class *ww_class;
@@ -137,6 +139,7 @@ static inline void ww_acquire_init(struct ww_acquire_ctx *ctx,
ctx->acquired = 0;
ctx->wounded = false;
ctx->is_wait_die = ww_class->is_wait_die;
+ wake_q_init(&ctx->wake_q);
#ifdef DEBUG_WW_MUTEXES
ctx->ww_class = ww_class;
ctx->done_acquire = 0;
diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index d973fe6041bf..1582756914df 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -676,6 +676,8 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
}

raw_spin_unlock(&lock->wait_lock);
+ if (ww_ctx)
+ ww_ctx_wake(ww_ctx);
schedule_preempt_disabled();

first = __mutex_waiter_is_first(lock, &waiter);
@@ -725,6 +727,8 @@ __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);
+ if (ww_ctx)
+ ww_ctx_wake(ww_ctx);
preempt_enable();
return 0;

@@ -736,6 +740,8 @@ __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);
+ if (ww_ctx)
+ ww_ctx_wake(ww_ctx);
preempt_enable();
return ret;
}
@@ -946,9 +952,11 @@ 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/ww_mutex.h b/kernel/locking/ww_mutex.h
index 56f139201f24..dfc174cd96c6 100644
--- a/kernel/locking/ww_mutex.h
+++ b/kernel/locking/ww_mutex.h
@@ -161,6 +161,11 @@ static inline void lockdep_assert_wait_lock_held(struct rt_mutex *lock)

#endif /* WW_RT */

+void ww_ctx_wake(struct ww_acquire_ctx *ww_ctx)
+{
+ wake_up_q(&ww_ctx->wake_q);
+}
+
/*
* Wait-Die:
* The newer transactions are killed when:
@@ -284,7 +289,7 @@ __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(&ww_ctx->wake_q, waiter->task);
}

return true;
@@ -331,7 +336,7 @@ 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(&ww_ctx->wake_q, owner);

return true;
}
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ee28253c9ac0..617e737392be 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1013,6 +1013,13 @@ void wake_up_q(struct wake_q_head *head)
wake_up_process(task);
put_task_struct(task);
}
+ /*
+ * XXX connoro: seems this is needed now that ww_ctx_wake() passes in a
+ * wake_q_head that is embedded in struct ww_acquire_ctx rather than
+ * declared locally.
+ */
+ head->first = node;
+ head->lastp = &head->first;
}

/*
--
2.38.0.rc1.362.ged0d419d3c-goog
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