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sched_ext: Factor out scx_rehome_task() and scx_punt_task()

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Factor out scx_rehome_task() and scx_punt_task() from the sub-disable
re-home loop and scx_fail_parent(). The upcoming cgroup migration re-homing
also needs scx_rehome_task(). No functional changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
This commit is contained in:
Tejun Heo 2026-07-17 22:12:20 -10:00
parent 52478777b3
commit 0dc90ce1be
1 changed files with 56 additions and 28 deletions
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84
kernel/sched/ext/sub.c
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@ -758,6 +758,57 @@ void drain_descendants(struct scx_sched *sch)
wait_event(scx_unlink_waitq, list_empty(&sch->children));
}
/**
* scx_rehome_task - Move a task to a sched it has been initialized for
* @to: sched taking over @p, @p's init on it already complete
* @p: task to re-home
*
* Exit @p from its current sched and switch it over to @to, overriding the
* state to %SCX_TASK_READY to account for the already completed init. A task
* on a non-ext class, possible under an %SCX_OPS_SWITCH_PARTIAL root, stays
* %READY and is enabled by switching_to_scx() if it switches over.
*/
static void scx_rehome_task(struct scx_sched *to, struct task_struct *p)
{
lockdep_assert_held(&p->pi_lock);
lockdep_assert_rq_held(task_rq(p));
scoped_guard (sched_change, p, DEQUEUE_SAVE | DEQUEUE_MOVE) {
scx_disable_and_exit_task(scx_task_sched(p), p);
scx_set_task_state(p, SCX_TASK_INIT_BEGIN);
scx_set_task_state(p, SCX_TASK_INIT);
scx_set_task_sched(p, to);
scx_set_task_state(p, SCX_TASK_READY);
if (p->sched_class == &ext_sched_class)
scx_enable_task(to, p);
}
}
/**
* scx_punt_task - Hand a task to a failed sched without initialization
* @to: failed and bypassed sched taking custody of @p
* @p: task to punt
*
* Take @p off its current sched and put it on @to at %SCX_TASK_NONE. @to is
* dying and its teardown will re-home @p properly.
*
* Used when @to must take over @p but failed to initialize it. Bypass keeps
* scheduling decisions away from @to but @p can still trigger its task ops,
* which may confuse the BPF side. @to is dying anyway. The exit paths skip
* %NONE tasks (see __scx_disable_and_exit_task() and switched_from_scx()).
*/
static void scx_punt_task(struct scx_sched *to, struct task_struct *p)
{
lockdep_assert_held(&p->pi_lock);
lockdep_assert_rq_held(task_rq(p));
WARN_ON_ONCE(!READ_ONCE(to->bypass_depth));
scoped_guard (sched_change, p, DEQUEUE_SAVE | DEQUEUE_MOVE) {
scx_disable_and_exit_task(scx_task_sched(p), p);
scx_set_task_sched(p, to);
}
}
static void scx_fail_parent(struct scx_sched *sch,
struct task_struct *failed, s32 fail_code)
{
@ -769,9 +820,9 @@ static void scx_fail_parent(struct scx_sched *sch,
fail_code, failed->comm, failed->pid);
/*
* Once $parent is bypassed, it's safe to put SCX_TASK_NONE tasks into
* it. This may cause downstream failures on the BPF side but $parent is
* dying anyway.
* Once $parent is bypassed, tasks can be punted into it. This may
* cause downstream failures on the BPF side but $parent is dying
* anyway.
*/
scx_bypass(parent, true);
@ -780,10 +831,7 @@ static void scx_fail_parent(struct scx_sched *sch,
if (scx_task_on_sched(parent, p))
continue;
scoped_guard (sched_change, p, DEQUEUE_SAVE | DEQUEUE_MOVE) {
scx_disable_and_exit_task(sch, p);
scx_set_task_sched(p, parent);
}
scx_punt_task(parent, p);
}
scx_task_iter_stop(&sti);
}
@ -881,27 +929,7 @@ void scx_sub_disable(struct scx_sched *sch)
continue;
}
scoped_guard (sched_change, p, DEQUEUE_SAVE | DEQUEUE_MOVE) {
/*
* $p is initialized for $parent and still attached to
* @sch. Disable and exit for @sch, switch over to
* $parent and override the state to READY to account
* for $p having already been initialized.
*/
scx_disable_and_exit_task(sch, p);
scx_set_task_state(p, SCX_TASK_INIT_BEGIN);
scx_set_task_state(p, SCX_TASK_INIT);
scx_set_task_sched(p, parent);
scx_set_task_state(p, SCX_TASK_READY);
/*
* A task on a non-ext class, possible under an
* %SCX_OPS_SWITCH_PARTIAL root, stays READY and is
* enabled by switching_to_scx() if it switches over.
*/
if (p->sched_class == &ext_sched_class)
scx_enable_task(parent, p);
}
scx_rehome_task(parent, p);
task_rq_unlock(rq, p, &rf);
put_task_struct(p);