linux-kernel - [PATCH sched_ext/for-6.19] sched_ext: Use SCX_TASK_READY test instead of tryget_task

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Message-ID: <31c2ba69c73dc25b022533ca00300256@kernel.org>
Date: Tue, 28 Oct 2025 11:04:18 -1000
From: Tejun Heo <tj@...nel.org>
To: David Vernet <void@...ifault.com>, Andrea Righi <arighi@...dia.com>, Changwoo Min <changwoo@...lia.com>
Cc: linux-kernel@...r.kernel.org, sched-ext@...ts.linux.dev
Subject: [PATCH sched_ext/for-6.19] sched_ext: Use SCX_TASK_READY test instead of tryget_task_struct() during class switch

ddf7233fcab6 ("sched/ext: Fix invalid task state transitions on class
switch") added tryget_task_struct() test during scx_enable()'s class
switching loop. The reason for the addition was to avoid enabling tasks which
skipped prep in the previous loop due to being dead.

While tryget_task_struct() does work for this purpose as tasks that fail
tryget always will fail it, it's a bit roundabout. A more direct way is
testing whether the task is in READY state. Switch to testing SCX_TASK_READY
directly.

Cc: Andrea Righi <arighi@...dia.com>
Signed-off-by: Tejun Heo <tj@...nel.org>
---
 kernel/sched/ext.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -4662,7 +4662,7 @@ static int scx_enable(struct sched_ext_o
 			__setscheduler_class(p->policy, p->prio);
 		struct sched_enq_and_set_ctx ctx;

-		if (!tryget_task_struct(p))
+		if (scx_get_task_state(p) != SCX_TASK_READY)
 			continue;

 		if (old_class != new_class && p->se.sched_delayed)
@@ -4677,7 +4677,6 @@ static int scx_enable(struct sched_ext_o
 		sched_enq_and_set_task(&ctx);

 		check_class_changed(task_rq(p), p, old_class, p->prio);
-		put_task_struct(p);
 	}
 	scx_task_iter_stop(&sti);
 	percpu_up_write(&scx_fork_rwsem);