[PATCH 4/9] tools/sched_ext: scx_pair: Don't attach after an interrupted initialization

[Tao Cui <cui.tao@linux.dev>]

From: Tao Cui <cuitao@kylinos.cn>

The cgrp_q_arr initialization loop checks exit_req and breaks early so
that Ctrl-C doesn't make the user wait through all MAX_CGRPS iterations
- but the break falls straight into SCX_OPS_ATTACH(). Attaching with
part of the inner queue maps missing lets ops.cgroup_init() hand out
slots for cgroups whose inner map was never created, and the first task
in such a cgroup aborts the scheduler with an scx_bpf_error(). On a busy
system the 4096-iteration loop takes long enough that hitting it with
Ctrl-C is likely, so the intended responsive interrupt turns into a
scheduler crash dump.

Exit cleanly when interrupted mid-initialization instead of attaching.

Fixes: f0262b102c7c ("tools/sched_ext: add scx_pair scheduler")
Signed-off-by: Tao Cui <cuitao@kylinos.cn>
---
 tools/sched_ext/scx_pair.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/tools/sched_ext/scx_pair.c b/tools/sched_ext/scx_pair.c
index 00f595b58f97..35c8a1a07f56 100644
--- a/tools/sched_ext/scx_pair.c
+++ b/tools/sched_ext/scx_pair.c
@@ -161,8 +161,17 @@ int main(int argc, char **argv)
 	printf("\n");
 
 	/*
-	 * Fully initialized, attach and run.
+	 * Fully initialized, attach and run. An interrupt during the
+	 * initialization loop leaves the tail of cgrp_q_arr without inner
+	 * maps; attaching in that state lets ops.cgroup_init() hand out
+	 * uninitialized slots and abort the scheduler on the first cgroup
+	 * task.
 	 */
+	if (exit_req) {
+		scx_pair__destroy(skel);
+		return 1;
+	}
+
 	link = SCX_OPS_ATTACH(skel, pair_ops, scx_pair);
 
 	while (!exit_req && !UEI_EXITED(skel, uei)) {
-- 
2.53.0

base-commit: 5b740a72b55c4267ba4d8010f17dde26b26f52d3