futex: Pull futex_hash() out of futex_q_lock()

Getting the hash bucket and queuing it are two distinct actions. In
light of wanting to add a put hash bucket function later, untangle
them.

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

Author: Peter Zijlstra

kernel/futex/core.c

@@ -502,13 +502,9 @@ void __futex_unqueue(struct futex_q *q)
 }
 
 /* The key must be already stored in q->key. */
-struct futex_hash_bucket *futex_q_lock(struct futex_q *q)
+void futex_q_lock(struct futex_q *q, struct futex_hash_bucket *hb)
 	__acquires(&hb->lock)
 {
-	struct futex_hash_bucket *hb;
-
-	hb = futex_hash(&q->key);
-
 	/*
 	 * Increment the counter before taking the lock so that
 	 * a potential waker won't miss a to-be-slept task that is
@@ -522,7 +518,6 @@ struct futex_hash_bucket *futex_q_lock(struct futex_q *q)
 	q->lock_ptr = &hb->lock;
 
 	spin_lock(&hb->lock);
-	return hb;
 }
 
 void futex_q_unlock(struct futex_hash_bucket *hb)

kernel/futex/futex.h

@@ -354,7 +354,7 @@ static inline int futex_hb_waiters_pending(struct futex_hash_bucket *hb)
 #endif
 }
 
-extern struct futex_hash_bucket *futex_q_lock(struct futex_q *q);
+extern void futex_q_lock(struct futex_q *q, struct futex_hash_bucket *hb);
 extern void futex_q_unlock(struct futex_hash_bucket *hb);
 
 

kernel/futex/pi.c

@@ -939,7 +939,8 @@ int futex_lock_pi(u32 __user *uaddr, unsigned int flags, ktime_t *time, int tryl
 		goto out;
 
 retry_private:
-	hb = futex_q_lock(&q);
+	hb = futex_hash(&q.key);
+	futex_q_lock(&q, hb);
 
 	ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current,
 				   &exiting, 0);

kernel/futex/waitwake.c

@@ -441,7 +441,8 @@ int futex_wait_multiple_setup(struct futex_vector *vs, int count, int *woken)
 		struct futex_q *q = &vs[i].q;
 		u32 val = vs[i].w.val;
 
-		hb = futex_q_lock(q);
+		hb = futex_hash(&q->key);
+		futex_q_lock(q, hb);
 		ret = futex_get_value_locked(&uval, uaddr);
 
 		if (!ret && uval == val) {
@@ -611,7 +612,8 @@ int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
 		return ret;
 
 retry_private:
-	hb = futex_q_lock(q);
+	hb = futex_hash(&q->key);
+	futex_q_lock(q, hb);
 
 	ret = futex_get_value_locked(&uval, uaddr);