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sched_ext: Handle SCX_TASK_NONE in disable/switched_from paths

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scx_fail_parent() leaves cgroup tasks at (state=NONE, sched=parent,
sched_class=ext) until the parent itself is torn down by the scx_error() it
raised. When the later root_disable iterates them, two paths trip on NONE.

scx_disable_and_exit_task() re-enters the wrapper at NONE: the inner switch
returns early but the trailing scx_set_task_sched(p, NULL) clobbers the
parent sched left by scx_fail_parent(), and scx_set_task_state(p, NONE)
wastes a write on an already-NONE task. switched_from_scx() then calls
scx_disable_task(), which WARNs on non-ENABLED state and writes state=READY,
producing a NONE -> READY transition the validation matrix rejects.

Treat NONE as "nothing to do" in both paths. Add a NONE early-return at the
top of scx_disable_and_exit_task() and a parallel NONE check in
switched_from_scx() next to task_dead_and_done().

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
This commit is contained in:
Tejun Heo
2026-05-10 10:08:16 -10:00
parent cd6aab7367
commit d3e73a0808
1 changed files with 19 additions and 0 deletions
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19
kernel/sched/ext.c
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@@ -3703,6 +3703,15 @@ 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);
/*
@@ -3921,6 +3930,16 @@ static void switched_from_scx(struct rq *rq, struct task_struct *p)
if (task_dead_and_done(p))
return;
/*
* %NONE means SCX is no longer tracking @p at the task level (e.g.
* scx_fail_parent() handed @p back to the parent at NONE pending the
* parent's own teardown). There is nothing to disable; calling
* scx_disable_task() would WARN on the non-%ENABLED state and trigger a
* NONE -> READY validation failure.
*/
if (scx_get_task_state(p) == SCX_TASK_NONE)
return;
scx_disable_task(scx_task_sched(p), p);
}