scx: Auto-release example scheduler struct_ops on program exit

When a BPF scheduler user-space program exits, the struct_ops map that
it attaches to to load the BPF program is not automatically detached.
This can cause the map and progs to remain loaded, which in turn will
cause future attempts to load a new scheduling program to fail.

In commit 8d1608d ("libbpf: Create a bpf_link in
bpf_map__attach_struct_ops()"), Kui-feng updated
bpf_map__attach_struct_ops() to create an actual link for the struct_ops
map, which in turn makes it automatically close the map when the owning
program exits. This patch updates the example schedulers to leverage
this by updating their sections to SEC(".struct_ops.link").

Signed-off-by: David Vernet <[email protected]>

Author: Byte-Lab

tools/sched_ext/atropos/src/bpf/atropos.bpf.c

@@ -723,7 +723,7 @@ void BPF_STRUCT_OPS(atropos_exit, struct scx_exit_info *ei)
 	exit_type = ei->type;
 }
 
-SEC(".struct_ops")
+SEC(".struct_ops.link")
 struct sched_ext_ops atropos = {
 	.select_cpu = (void *)atropos_select_cpu,
 	.enqueue = (void *)atropos_enqueue,

tools/sched_ext/scx_example_central.bpf.c

@@ -314,7 +314,7 @@ void BPF_STRUCT_OPS(central_exit, struct scx_exit_info *ei)
 	uei_record(&uei, ei);
 }
 
-SEC(".struct_ops")
+SEC(".struct_ops.link")
 struct sched_ext_ops central_ops = {
 	/*
 	 * We are offloading all scheduling decisions to the central CPU and

tools/sched_ext/scx_example_flatcg.bpf.c

@@ -853,7 +853,7 @@ void BPF_STRUCT_OPS(fcg_exit, struct scx_exit_info *ei)
 	uei_record(&uei, ei);
 }
 
-SEC(".struct_ops")
+SEC(".struct_ops.link")
 struct sched_ext_ops flatcg_ops = {
 	.enqueue		= (void *)fcg_enqueue,
 	.dispatch		= (void *)fcg_dispatch,

tools/sched_ext/scx_example_pair.bpf.c

@@ -613,7 +613,7 @@ void BPF_STRUCT_OPS(pair_exit, struct scx_exit_info *ei)
 	uei_record(&uei, ei);
 }
 
-SEC(".struct_ops")
+SEC(".struct_ops.link")
 struct sched_ext_ops pair_ops = {
 	.enqueue		= (void *)pair_enqueue,
 	.dispatch		= (void *)pair_dispatch,

tools/sched_ext/scx_example_qmap.bpf.c

@@ -384,7 +384,7 @@ void BPF_STRUCT_OPS(qmap_exit, struct scx_exit_info *ei)
 	uei_record(&uei, ei);
 }
 
-SEC(".struct_ops")
+SEC(".struct_ops.link")
 struct sched_ext_ops qmap_ops = {
 	.select_cpu		= (void *)qmap_select_cpu,
 	.enqueue		= (void *)qmap_enqueue,

tools/sched_ext/scx_example_simple.bpf.c

@@ -117,7 +117,7 @@ void BPF_STRUCT_OPS(simple_exit, struct scx_exit_info *ei)
 	uei_record(&uei, ei);
 }
 
-SEC(".struct_ops")
+SEC(".struct_ops.link")
 struct sched_ext_ops simple_ops = {
 	.enqueue		= (void *)simple_enqueue,
 	.running		= (void *)simple_running,

tools/sched_ext/scx_example_userland.bpf.c

@@ -249,7 +249,7 @@ void BPF_STRUCT_OPS(userland_exit, struct scx_exit_info *ei)
 	uei_record(&uei, ei);
 }
 
-SEC(".struct_ops")
+SEC(".struct_ops.link")
 struct sched_ext_ops userland_ops = {
 	.select_cpu		= (void *)userland_select_cpu,
 	.enqueue		= (void *)userland_enqueue,