sched/proxy: Switch proxy to use p->is_blocked

Rather than gate the proxy paths with p->blocked_on, use p->is_blocked.

This opens up the state: '->is_blocked && !->blocked_on' for future use.

Notably, only proxy and delayed tasks can be ->on_rq && ->is_blocked, and it is
guaranteed that sched_class::pick_task() will never return a delayed task.
Therefore any task returned from pick_next_task() that has ->is_blocked set,
must be a proxy task.

Suggested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260526113322.477954312%40infradead.org

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index b007b65d9c88fc5078e72e1e09eb4ac18f1b0020..9b710313dfb34b5999ab7e0eee251b1dd93b5e15 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3764,7 +3764,7 @@ static inline void proxy_reset_donor(struct rq *rq)
  */
 static inline bool proxy_needs_return(struct rq *rq, struct task_struct *p)
 {
-       if (!task_is_blocked(p))
+       if (!p->is_blocked)
                return false;
 
        /*
@@ -6866,14 +6866,14 @@ find_proxy_task(struct rq *rq, struct task_struct *donor, struct rq_flags *rf)
        bool curr_in_chain = false;
        int this_cpu = cpu_of(rq);
        struct task_struct *p;
-       struct mutex *mutex;
        int owner_cpu;
 
        /* Follow blocked_on chain. */
-       for (p = donor; (mutex = p->blocked_on); p = owner) {
+       for (p = donor; p->is_blocked; p = owner) {
                /* if its PROXY_WAKING, do return migration or run if current */
-               if (mutex == PROXY_WAKING) {
-                       clear_task_blocked_on(p, PROXY_WAKING);
+               struct mutex *mutex = p->blocked_on;
+               if (!mutex || mutex == PROXY_WAKING) {
+                       clear_task_blocked_on(p, mutex);
                        if (task_current(rq, p)) {
                                p->is_blocked = 0;
                                return p;
@@ -7147,7 +7147,7 @@ pick_again:
 
                rq_set_donor(rq, next);
                next->blocked_donor = NULL;
-               if (unlikely(next->is_blocked && next->blocked_on)) {
+               if (unlikely(next->is_blocked)) {
                        next = find_proxy_task(rq, next, &rf);
                        if (!next) {
                                zap_balance_callbacks(rq);