From cceb8fa9cb2cf98e31d81ecf6353b6ba5ac57744 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Sun, 10 May 2026 10:08:16 -1000 Subject: [PATCH] sched_ext: Replace SCX_TASK_OFF_TASKS flag with SCX_TASK_DEAD state SCX_TASK_OFF_TASKS marked tasks already through sched_ext_dead() so cgroup task iteration would skip them. This can be expressed better with a task state. Replace the flag with SCX_TASK_DEAD. scx_disable_and_exit_task() resets state to NONE on its way out, so sched_ext_dead() now sets DEAD after the wrapper returns. The validation matrix grows NONE -> DEAD, warns on DEAD -> NONE, and tightens READY's predecessor to INIT or ENABLED so the new DEAD value cannot silently transition to READY. Prepares for the following enable vs dead race fix. Signed-off-by: Tejun Heo Reviewed-by: Andrea Righi --- include/linux/sched/ext.h | 9 +++++---- kernel/sched/ext.c | 17 +++++++++++------ 2 files changed, 16 insertions(+), 10 deletions(-) diff --git a/include/linux/sched/ext.h b/include/linux/sched/ext.h index adb9a4de068a..9f1a326ad03e 100644 --- a/include/linux/sched/ext.h +++ b/include/linux/sched/ext.h @@ -101,24 +101,25 @@ enum scx_ent_flags { SCX_TASK_DEQD_FOR_SLEEP = 1 << 3, /* last dequeue was for SLEEP */ SCX_TASK_SUB_INIT = 1 << 4, /* task being initialized for a sub sched */ SCX_TASK_IMMED = 1 << 5, /* task is on local DSQ with %SCX_ENQ_IMMED */ - SCX_TASK_OFF_TASKS = 1 << 6, /* removed from scx_tasks by sched_ext_dead() */ /* - * Bits 8 and 9 are used to carry task state: + * Bits 8 to 10 are used to carry task state: * * NONE ops.init_task() not called yet * INIT ops.init_task() succeeded, but task can be cancelled * READY fully initialized, but not in sched_ext * ENABLED fully initialized and in sched_ext + * DEAD terminal state set by sched_ext_dead() */ - SCX_TASK_STATE_SHIFT = 8, /* bits 8 and 9 are used to carry task state */ - SCX_TASK_STATE_BITS = 2, + SCX_TASK_STATE_SHIFT = 8, + SCX_TASK_STATE_BITS = 3, SCX_TASK_STATE_MASK = ((1 << SCX_TASK_STATE_BITS) - 1) << SCX_TASK_STATE_SHIFT, SCX_TASK_NONE = 0 << SCX_TASK_STATE_SHIFT, SCX_TASK_INIT = 1 << SCX_TASK_STATE_SHIFT, SCX_TASK_READY = 2 << SCX_TASK_STATE_SHIFT, SCX_TASK_ENABLED = 3 << SCX_TASK_STATE_SHIFT, + SCX_TASK_DEAD = 4 << SCX_TASK_STATE_SHIFT, /* * Bits 12 and 13 are used to carry reenqueue reason. In addition to diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c index 81841277a54f..2fc4a12711f9 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -723,17 +723,22 @@ static void scx_set_task_state(struct task_struct *p, u32 state) switch (state) { case SCX_TASK_NONE: + warn = prev_state == SCX_TASK_DEAD; break; case SCX_TASK_INIT: warn = prev_state != SCX_TASK_NONE; p->scx.flags |= SCX_TASK_RESET_RUNNABLE_AT; break; case SCX_TASK_READY: - warn = prev_state == SCX_TASK_NONE; + warn = !(prev_state == SCX_TASK_INIT || + prev_state == SCX_TASK_ENABLED); break; case SCX_TASK_ENABLED: warn = prev_state != SCX_TASK_READY; break; + case SCX_TASK_DEAD: + warn = prev_state != SCX_TASK_NONE; + break; default: WARN_ONCE(1, "sched_ext: Invalid task state %d -> %d for %s[%d]", prev_state, state, p->comm, p->pid); @@ -972,11 +977,11 @@ static struct task_struct *scx_task_iter_next_locked(struct scx_task_iter *iter) /* * cgroup_task_dead() removes the dead tasks from cset->tasks * after sched_ext_dead() and cgroup iteration may see tasks - * which already finished sched_ext_dead(). %SCX_TASK_OFF_TASKS - * is set by sched_ext_dead() under @p's rq lock. Test it to + * which already finished sched_ext_dead(). %SCX_TASK_DEAD is + * set by sched_ext_dead() under @p's rq lock. Test it to * avoid visiting tasks which are already dead from SCX POV. */ - if (p->scx.flags & SCX_TASK_OFF_TASKS) { + if (scx_get_task_state(p) == SCX_TASK_DEAD) { __scx_task_iter_rq_unlock(iter); continue; } @@ -3847,7 +3852,7 @@ void sched_ext_dead(struct task_struct *p) * @p is off scx_tasks and wholly ours. scx_root_enable()'s READY -> * ENABLED transitions can't race us. Disable ops for @p. * - * %SCX_TASK_OFF_TASKS synchronizes against cgroup task iteration - see + * %SCX_TASK_DEAD synchronizes against cgroup task iteration - see * scx_task_iter_next_locked(). NONE tasks need no marking: cgroup * iteration is only used from sub-sched paths, which require root * enabled. Root enable transitions every live task to at least READY. @@ -3858,7 +3863,7 @@ void sched_ext_dead(struct task_struct *p) rq = task_rq_lock(p, &rf); scx_disable_and_exit_task(scx_task_sched(p), p); - p->scx.flags |= SCX_TASK_OFF_TASKS; + scx_set_task_state(p, SCX_TASK_DEAD); task_rq_unlock(rq, p, &rf); } } -- 2.47.3