Merge branch 'for-7.1-fixes' into for-7.2

Pull to receive:

 39e25a210060 ("sched_ext: Drop NONE early return in scx_disable_and_exit_task()")
 b273b75b8d67 ("sched_ext: INIT_LIST_HEAD() &sch->all in scx_alloc_and_add_sched()")
 cceb874eee46 ("sched_ext: Defer sub_kset base put to scx_sched_free_rcu_work")
 6ae315d37924 ("sched_ext: Use HK_TYPE_DOMAIN_BOOT to detect isolcpus= domain isolation")
 515e3996a4c2 ("sched_ext: Fix deadlock between scx_root_disable() and concurrent forks")

to prepare for-7.2 for further sub-sched changes.

Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 29 insertions, 15 deletions

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 64f8a096f133..9c458552d14f 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -3816,22 +3816,14 @@ static void scx_sub_init_cancel_task(struct scx_sched *sch, struct task_struct *
 static void scx_disable_and_exit_task(struct scx_sched *sch,
 				      struct task_struct *p)
 {
-	/*
-	 * %NONE means @p is already detached at the SCX level (e.g. handed
-	 * back to the parent by scx_fail_parent() with no init to undo).
-	 * Skip to avoid clobbering scx_task_sched() and writing %NONE again
-	 * on a state that's already %NONE.
-	 */
-	if (scx_get_task_state(p) == SCX_TASK_NONE)
-		return;
-
 	__scx_disable_and_exit_task(sch, p);
 
 	/*
 	 * If set, @p exited between __scx_init_task() and scx_enable_task() in
 	 * scx_sub_enable() and is initialized for both the associated sched and
 	 * its parent. Exit for the child too - scx_enable_task() never ran for
-	 * it, so undo only init_task.
+	 * it, so undo only init_task. The flag is only set on the sub-enable
+	 * path, so it's always clear when @p arrives here in %SCX_TASK_NONE.
 	 */
 	if (p->scx.flags & SCX_TASK_SUB_INIT) {
 		if (!WARN_ON_ONCE(!scx_enabling_sub_sched))
@@ -4975,6 +4967,8 @@ static void scx_sched_free_rcu_work(struct work_struct *work)
 	kfree(sch->cgrp_path);
 	if (sch_cgroup(sch))
 		cgroup_put(sch_cgroup(sch));
+	if (sch->sub_kset)
+		kobject_put(&sch->sub_kset->kobj);
 #endif	/* CONFIG_EXT_SUB_SCHED */
 
 	for_each_possible_cpu(cpu) {
@@ -5098,10 +5092,30 @@ static const struct kset_uevent_ops scx_uevent_ops = {
  */
 bool task_should_scx(int policy)
 {
-	if (!scx_enabled() || unlikely(scx_enable_state() == SCX_DISABLING))
+	/* if disabled, nothing should be on it */
+	if (!scx_enabled())
 		return false;
+
+	/* scx is taking over all SCHED_OTHER and SCHED_EXT tasks */
 	if (READ_ONCE(scx_switching_all))
 		return true;
+
+	/*
+	 * scx is tearing down - keep new SCHED_EXT tasks out.
+	 *
+	 * Must come after scx_switching_all test, which serves as a proxy
+	 * for __scx_switched_all. While __scx_switched_all is set, we must
+	 * return true via the branch above: a fork routed to fair would
+	 * stall because next_active_class() skips fair.
+	 *
+	 * This can develop into a deadlock - scx holds scx_enable_mutex across
+	 * kthread_create() in scx_alloc_and_add_sched(); if the new kthread is
+	 * the stalled task, the disable path can never grab the mutex to clear
+	 * scx_switching_all.
+	 */
+	if (unlikely(scx_enable_state() == SCX_DISABLING))
+		return false;
+
 	return policy == SCHED_EXT;
 }
 
@@ -6035,7 +6049,7 @@ static void scx_sub_disable(struct scx_sched *sch)
 	if (sch->ops.exit)
 		SCX_CALL_OP(sch, exit, NULL, sch->exit_info);
 	if (sch->sub_kset)
-		kset_unregister(sch->sub_kset);
+		kobject_del(&sch->sub_kset->kobj);
 	kobject_del(&sch->kobj);
 }
 #else	/* CONFIG_EXT_SUB_SCHED */
@@ -6161,7 +6175,7 @@ static void scx_root_disable(struct scx_sched *sch)
 	 */
 #ifdef CONFIG_EXT_SUB_SCHED
 	if (sch->sub_kset)
-		kset_unregister(sch->sub_kset);
+		kobject_del(&sch->sub_kset->kobj);
 #endif
 	kobject_del(&sch->kobj);
 
@@ -6850,6 +6864,7 @@ static struct scx_sched *scx_alloc_and_add_sched(struct scx_enable_cmd *cmd,
 	rcu_assign_pointer(ops->priv, sch);
 
 	sch->kobj.kset = scx_kset;
+	INIT_LIST_HEAD(&sch->all);
 
 #ifdef CONFIG_EXT_SUB_SCHED
 	char *buf = kzalloc(PATH_MAX, GFP_KERNEL);
@@ -7677,8 +7692,7 @@ static s32 scx_enable(struct scx_enable_cmd *cmd, struct bpf_link *link)
 	static struct kthread_worker *helper;
 	static DEFINE_MUTEX(helper_mutex);
 
-	if (!cpumask_equal(housekeeping_cpumask(HK_TYPE_DOMAIN),
-			   cpu_possible_mask)) {
+	if (housekeeping_enabled(HK_TYPE_DOMAIN_BOOT)) {
 		pr_err("sched_ext: Not compatible with \"isolcpus=\" domain isolation\n");
 		return -EINVAL;
 	}