sched_ext: Drop NONE early return in scx_disable_and_exit_task()

d3e73a0808dd ("sched_ext: Handle SCX_TASK_NONE in disable/switched_from
paths") skipped the trailing scx_set_task_sched(p, NULL) on NONE tasks.
After scx_fail_parent() parks a task at NONE/sched=parent and the parent
is later freed via queue_rcu_work() during root_disable, the preserved
p->scx.sched dangles - print_scx_info() from sched_show_task() reads
sch->ops.name from freed memory.

Drop the early return. __scx_disable_and_exit_task() already short-
circuits on NONE and the SUB_INIT block was cleared by
scx_fail_parent()'s earlier call, so clearing p->scx.sched is the only
work left - and the one thing the path actually needs.

v2: Extend the SUB_INIT block comment to note that the flag is only
    set on the sub-enable path, so it's always clear on the NONE
    re-entry (Andrea).

Fixes: d3e73a0808dd ("sched_ext: Handle SCX_TASK_NONE in disable/switched_from paths")
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 9354da79e162a73e15d60bbac4a6d28235b34fd5..68120f679178dad07a88cf7d5fbca1238e0ec066 100644 (file)
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -3703,22 +3703,14 @@ 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))