From d7832ba1a4a4f462ce94c81960adf10f7e87ae7a Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Fri, 14 Aug 2026 07:46:46 -1000 Subject: [PATCH] sched_ext: Set up ops.sub_ecaps_updated() dispatch context on the executing CPU scx_process_sync_ecaps() sets up the dispatch context for ops.sub_ecaps_updated() in the target cpu's pcpu context recovered from the llist node. However, the context is per executing cpu: the dispatch kfuncs resolve it with this_cpu_ptr() and the dispatch buffer lives in it. What the dispatches target is determined by the rq recorded in the context, not by which cpu's context it is. Under core scheduling the pick runs balance_one() for sibling rqs, so a sync processed for a sibling invokes the op with the executing cpu's context not set up and its dispatch kfuncs misoperate on a NULL or stale rq. Set up the executing cpu's dsp_ctx instead, matching scx_dispatch_sched(). The recorded rq keeps the dispatches targeting the synced cpu. Fixes: b81a6c018cde ("sched_ext: Add sub_ecaps_updated() effective-cap change notifier") Reported-by: David Carlier Link: https://lore.kernel.org/all/20260813045931.8691-1-devnexen@gmail.com/ Signed-off-by: Tejun Heo --- kernel/sched/ext/sub.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/kernel/sched/ext/sub.c b/kernel/sched/ext/sub.c index 3bd12c1ff0a3..ec4729c99763 100644 --- a/kernel/sched/ext/sub.c +++ b/kernel/sched/ext/sub.c @@ -1017,11 +1017,15 @@ void scx_process_sync_ecaps(struct rq *rq, struct task_struct *prev) * invocation is equivalent to the dispatch path and may drop * and re-acquire the rq lock temporarily while the rest of * @batch is held privately, see scx_discard_ecaps_to_sync(). + * The dispatch kfuncs resolve their context on the executing + * cpu, which under core scheduling can differ from @rq's cpu, + * so the context is set up there. The rq recorded in it keeps + * the dispatches targeting @rq. */ if (ecaps != pcpu->reported_ecaps && SCX_HAS_OP(pcpu->sch, sub_ecaps_updated) && !scx_bypassing(pcpu->sch, cpu)) { - struct scx_dsp_ctx *dspc = &pcpu->dsp_ctx; + struct scx_dsp_ctx *dspc = &this_cpu_ptr(pcpu->sch->pcpu)->dsp_ctx; dspc->rq = rq; /* stash @prev so nested dispatches can access it */