linux-kernel - [PATCH 5/6] locking/rwsem: Unify wait loop

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Date:   Thu, 23 Feb 2023 13:26:47 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     longman@...hat.com, mingo@...hat.com, will@...nel.org
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        boqun.feng@...il.com
Subject: [PATCH 5/6] locking/rwsem: Unify wait loop

Now that the reader and writer wait loops are identical, share the
code.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 kernel/locking/rwsem.c |  117 +++++++++++++++++++------------------------------
 1 file changed, 47 insertions(+), 70 deletions(-)

--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -650,13 +650,11 @@ static void rwsem_mark_wake(struct rw_se
  * optionally wake up waiters before it returns.
  */
 static inline void
-rwsem_del_wake_waiter(struct rw_semaphore *sem, struct rwsem_waiter *waiter,
-		      struct wake_q_head *wake_q)
+rwsem_del_wake_waiter(struct rw_semaphore *sem, struct rwsem_waiter *waiter)
 		      __releases(&sem->wait_lock)
 {
 	bool first = rwsem_first_waiter(sem) == waiter;
-
-	wake_q_init(wake_q);
+	DEFINE_WAKE_Q(wake_q);
 
 	/*
 	 * If the wait_list isn't empty and the waiter to be deleted is
@@ -664,10 +662,10 @@ rwsem_del_wake_waiter(struct rw_semaphor
 	 * be eligible to acquire or spin on the lock.
 	 */
 	if (rwsem_del_waiter(sem, waiter) && first)
-		rwsem_mark_wake(sem, RWSEM_WAKE_ANY, wake_q);
+		rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
 	raw_spin_unlock_irq(&sem->wait_lock);
-	if (!wake_q_empty(wake_q))
-		wake_up_q(wake_q);
+	if (!wake_q_empty(&wake_q))
+		wake_up_q(&wake_q);
 }
 
 /*
@@ -993,6 +991,46 @@ static inline void rwsem_cond_wake_waite
 	rwsem_mark_wake(sem, wake_type, wake_q);
 }
 
+#define waiter_type(_waiter, _r, _w)	\
+	((_waiter)->type == RWSEM_WAITING_FOR_READ ? (_r) : (_w))
+
+static __always_inline struct rw_semaphore *
+rwsem_waiter_wait(struct rw_semaphore *sem, struct rwsem_waiter *waiter, int state)
+{
+	trace_contention_begin(sem, waiter_type(waiter, LCB_F_READ, LCB_F_WRITE));
+
+	/* wait to be given the lock */
+	for (;;) {
+		set_current_state(state);
+		if (!smp_load_acquire(&waiter->task)) {
+			/* Matches rwsem_waiter_wake()'s smp_store_release(). */
+			break;
+		}
+		if (signal_pending_state(state, current)) {
+			raw_spin_lock_irq(&sem->wait_lock);
+			if (waiter->task)
+				goto out_nolock;
+			raw_spin_unlock_irq(&sem->wait_lock);
+			/* Ordered by sem->wait_lock against rwsem_mark_wake(). */
+			break;
+		}
+		schedule_preempt_disabled();
+		lockevent_inc(waiter_type(waiter, rwsem_sleep_reader, rwsem_sleep_writer));
+	}
+
+	__set_current_state(TASK_RUNNING);
+	lockevent_inc(waiter_type(waiter, rwsem_rlock, rwsem_wlock));
+	trace_contention_end(sem, 0);
+	return sem;
+
+out_nolock:
+	rwsem_del_wake_waiter(sem, waiter);
+	__set_current_state(TASK_RUNNING);
+	lockevent_inc(waiter_type(waiter, rwsem_rlock_fail, rwsem_wlock_fail));
+	trace_contention_end(sem, -EINTR);
+	return ERR_PTR(-EINTR);
+}
+
 /*
  * Wait for the read lock to be granted
  */
@@ -1071,38 +1109,7 @@ rwsem_down_read_slowpath(struct rw_semap
 	if (!wake_q_empty(&wake_q))
 		wake_up_q(&wake_q);
 
-	trace_contention_begin(sem, LCB_F_READ);
-
-	/* wait to be given the lock */
-	for (;;) {
-		set_current_state(state);
-		if (!smp_load_acquire(&waiter.task)) {
-			/* Matches rwsem_waiter_wake()'s smp_store_release(). */
-			break;
-		}
-		if (signal_pending_state(state, current)) {
-			raw_spin_lock_irq(&sem->wait_lock);
-			if (waiter.task)
-				goto out_nolock;
-			raw_spin_unlock_irq(&sem->wait_lock);
-			/* Ordered by sem->wait_lock against rwsem_mark_wake(). */
-			break;
-		}
-		schedule_preempt_disabled();
-		lockevent_inc(rwsem_sleep_reader);
-	}
-
-	__set_current_state(TASK_RUNNING);
-	lockevent_inc(rwsem_rlock);
-	trace_contention_end(sem, 0);
-	return sem;
-
-out_nolock:
-	rwsem_del_wake_waiter(sem, &waiter, &wake_q);
-	__set_current_state(TASK_RUNNING);
-	lockevent_inc(rwsem_rlock_fail);
-	trace_contention_end(sem, -EINTR);
-	return ERR_PTR(-EINTR);
+	return rwsem_waiter_wait(sem, &waiter, state);
 }
 
 /*
@@ -1150,37 +1157,7 @@ rwsem_down_write_slowpath(struct rw_sema
 	}
 	raw_spin_unlock_irq(&sem->wait_lock);
 
-	/* wait until we successfully acquire the lock */
-	trace_contention_begin(sem, LCB_F_WRITE);
-
-	for (;;) {
-		set_current_state(state);
-		if (!smp_load_acquire(&waiter.task)) {
-			/* Matches rwsem_waiter_wake()'s smp_store_release(). */
-			break;
-		}
-		if (signal_pending_state(state, current)) {
-			raw_spin_lock_irq(&sem->wait_lock);
-			if (waiter.task)
-				goto out_nolock;
-			raw_spin_unlock_irq(&sem->wait_lock);
-			/* Ordered by sem->wait_lock against rwsem_mark_wake(). */
-			break;
-		}
-		schedule_preempt_disabled();
-		lockevent_inc(rwsem_sleep_writer);
-	}
-	__set_current_state(TASK_RUNNING);
-	lockevent_inc(rwsem_wlock);
-	trace_contention_end(sem, 0);
-	return sem;
-
-out_nolock:
-	rwsem_del_wake_waiter(sem, &waiter, &wake_q);
-	__set_current_state(TASK_RUNNING);
-	lockevent_inc(rwsem_wlock_fail);
-	trace_contention_end(sem, -EINTR);
-	return ERR_PTR(-EINTR);
+	return rwsem_waiter_wait(sem, &waiter, state);
 }
 
 /*