[PATCH 3/5] sched_ext: Report NMI kicks with scx_error()

[Tejun Heo]

The per-cpu kick lists are protected by IRQ masking which doesn't stop NMIs,
so scx_bpf_kick_cpu() from NMI silently drops the kick after a one-time
warning. A dropped kick can leave a CPU idle when the scheduler believes it
was woken, which is a correctness problem for the scheduler even if the
kernel is fine. Now that scx_error() works from NMI, abort the scheduler
instead so that the bug is surfaced deterministically. The warned_nmi_kick
tracking is no longer needed.

Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
---
 kernel/sched/ext/ext.c      | 6 +-----
 kernel/sched/ext/internal.h | 1 -
 2 files changed, 1 insertion(+), 6 deletions(-)

diff --git a/kernel/sched/ext/ext.c b/kernel/sched/ext/ext.c
index 29ca5f5ec30b..4338dc6a3f3a 100644
--- a/kernel/sched/ext/ext.c
+++ b/kernel/sched/ext/ext.c
@@ -9208,11 +9208,7 @@ void scx_kick_cpu(struct scx_sched *sch, s32 cpu, u64 flags)
 	 * not mask NMIs, so kicking from NMI could corrupt it and is unsupported.
 	 */
 	if (unlikely(in_nmi())) {
-		if (!sch->warned_nmi_kick) {
-			sch->warned_nmi_kick = true;
-			pr_warn("sched_ext: %s: scx_bpf_kick_cpu() from NMI ignored\n",
-				sch->ops.name);
-		}
+		scx_error(sch, "scx_bpf_kick_cpu() called from NMI");
 		return;
 	}
 
diff --git a/kernel/sched/ext/internal.h b/kernel/sched/ext/internal.h
index a0659f74b065..b141f0104b44 100644
--- a/kernel/sched/ext/internal.h
+++ b/kernel/sched/ext/internal.h
@@ -1546,7 +1546,6 @@ struct scx_sched {
 	 */
 	bool			warned_zero_slice:1;
 	bool			warned_unassoc_progs:1;
-	bool			warned_nmi_kick:1;
 
 	struct list_head	all;
 
-- 
2.55.0