[RFC PATCH 09/12] futex: Wake up donor in PING futex unlock.

[Suleiman Souhlal]

Now that PING blockers can act as donors, it makes sense to wake up
the donor instead of the top_waiter when unlocking.

Signed-off-by: Suleiman Souhlal <suleiman@xxxxxxxxxx>
---
 kernel/futex/ping.c | 56 +++++++++++++++++++++++++++++++++++++--------
 1 file changed, 46 insertions(+), 10 deletions(-)

diff --git a/kernel/futex/ping.c b/kernel/futex/ping.c
index 5bf2293bf582..df701b437f16 100644
--- a/kernel/futex/ping.c
+++ b/kernel/futex/ping.c
@@ -478,10 +478,46 @@ int futex_lock_ping(u32 __user *uaddr, unsigned int flags, ktime_t *time,
 	return ret;
 }
 
+#ifdef CONFIG_SCHED_PROXY_EXEC
+static inline
+struct task_struct *ping_current_proxy_donor(struct futex_pi_state *ping_state)
+{
+	struct task_struct *ret = NULL;
+
+	if (sched_proxy_exec()) {
+		struct task_struct *donor;
+
+		raw_spin_lock(&current->blocked_lock);
+		donor = current->blocked_donor;
+		if (donor) {
+			void *ping_lock = (void *)&ping_state->ping_mutex;
+
+			raw_spin_lock_nested(&donor->blocked_lock,
+					     SINGLE_DEPTH_NESTING);
+			if (__get_task_blocked_on(donor) == ping_lock) {
+				ret = get_task_struct(donor);
+				__clear_task_blocked_on(donor, ping_lock);
+				current->blocked_donor = NULL;
+			}
+			raw_spin_unlock(&donor->blocked_lock);
+		}
+		raw_spin_unlock(&current->blocked_lock);
+	}
+	return ret;
+}
+#else
+static inline
+struct task_struct *ping_current_proxy_donor(struct futex_pi_state *ping_state)
+{
+	return NULL;
+}
+#endif
+
 int futex_unlock_ping(u32 __user *uaddr, unsigned int flags)
 {
 	struct futex_pi_state *ping_state;
 	u32 new, uval, vpid = task_pid_vnr(current);
+	struct task_struct *next;
 	union futex_key key = FUTEX_KEY_INIT;
 	struct futex_q *top_waiter;
 	DEFINE_WAKE_Q(wake_q);
@@ -528,15 +564,15 @@ int futex_unlock_ping(u32 __user *uaddr, unsigned int flags)
 	if (!ping_state)
 		goto out_unlock;
 	raw_spin_lock_irq(&ping_state->ping_mutex.wait_lock);
-	if (ping_state->owner != current) {
-		raw_spin_unlock_irq(&ping_state->ping_mutex.wait_lock);
-		goto out_unlock;
-	}
+
+	next = ping_current_proxy_donor(ping_state);
 	get_ping_state(ping_state);
 	/* Leave it queued, it gets unqueued on the lock side */
-	get_task_struct(top_waiter->task);
-	wake_q_add_safe(&wake_q, top_waiter->task);
-	clear_task_blocked_on(top_waiter->task, &ping_state->ping_mutex);
+	if (next == NULL) {
+		next = get_task_struct(top_waiter->task);
+		clear_task_blocked_on(next, &ping_state->ping_mutex);
+	}
+	wake_q_add_safe(&wake_q, next);
 	spin_unlock(&hb->lock);
 
 	/*
@@ -546,10 +582,10 @@ int futex_unlock_ping(u32 __user *uaddr, unsigned int flags)
 	 */
 	new = FUTEX_WAITERS;
 	if (ping_state->handoff) {
-		new |= task_pid_vnr(top_waiter->task);
+		new |= task_pid_vnr(next);
 		ping_state->handoff = 0;
 		ping_state->pickup = 1;
-		WRITE_ONCE(ping_state->ping_mutex.owner, top_waiter->task);
+		WRITE_ONCE(ping_state->ping_mutex.owner, next);
 	} else
 		WRITE_ONCE(ping_state->ping_mutex.owner, NULL);
 	ret = lock_pi_update_atomic(uaddr, uval, new);
@@ -568,7 +604,7 @@ int futex_unlock_ping(u32 __user *uaddr, unsigned int flags)
 		}
 	}
 
-	ping_state_update_owner(ping_state, top_waiter->task);
+	ping_state_update_owner(ping_state, next);
 	raw_spin_unlock_irq_wake(&ping_state->ping_mutex.wait_lock, &wake_q);
 	put_ping_state(ping_state);
 	return 0;
-- 
2.55.0.1082.g2b9226bbc0-goog