[PATCH 17/31] sched_ext: Add sysrq-S which disables the BPF scheduler

[Tejun Heo <tj@kernel.org>]

This enables the admin to abort the BPF scheduler and revert to CFS anytime.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: David Vernet <dvernet@meta.com>
Acked-by: Josh Don <joshdon@google.com>
Acked-by: Hao Luo <haoluo@google.com>
Acked-by: Barret Rhoden <brho@google.com>
---
 drivers/tty/sysrq.c         |  1 +
 include/linux/sched/ext.h   |  1 +
 kernel/sched/build_policy.c |  1 +
 kernel/sched/ext.c          | 20 ++++++++++++++++++++
 4 files changed, 23 insertions(+)

diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index d2b2720db6ca..b3c22bf5f0d1 100644
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -520,6 +520,7 @@ static const struct sysrq_key_op *sysrq_key_table[62] = {
 	NULL,				/* P */
 	NULL,				/* Q */
 	NULL,				/* R */
+	/* S: May be registered by sched_ext for resetting */
 	NULL,				/* S */
 	NULL,				/* T */
 	NULL,				/* U */
diff --git a/include/linux/sched/ext.h b/include/linux/sched/ext.h
index e2e743ccd00d..1ec8be53057f 100644
--- a/include/linux/sched/ext.h
+++ b/include/linux/sched/ext.h
@@ -55,6 +55,7 @@ enum scx_exit_type {
 	SCX_EXIT_DONE,
 
 	SCX_EXIT_UNREG = 64,	/* BPF unregistration */
+	SCX_EXIT_SYSRQ,		/* requested by 'S' sysrq */
 
 	SCX_EXIT_ERROR = 1024,	/* runtime error, error msg contains details */
 	SCX_EXIT_ERROR_BPF,	/* ERROR but triggered through scx_bpf_error() */
diff --git a/kernel/sched/build_policy.c b/kernel/sched/build_policy.c
index 4c658b21f603..005025f55bea 100644
--- a/kernel/sched/build_policy.c
+++ b/kernel/sched/build_policy.c
@@ -28,6 +28,7 @@
 #include <linux/suspend.h>
 #include <linux/tsacct_kern.h>
 #include <linux/vtime.h>
+#include <linux/sysrq.h>
 #include <linux/percpu-rwsem.h>
 
 #include <uapi/linux/sched/types.h>
diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 1428385093dc..a0057a8447cb 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -1771,6 +1771,9 @@ static void scx_ops_disable_workfn(struct kthread_work *work)
 	case SCX_EXIT_UNREG:
 		reason = "BPF scheduler unregistered";
 		break;
+	case SCX_EXIT_SYSRQ:
+		reason = "disabled by sysrq-S";
+		break;
 	case SCX_EXIT_ERROR:
 		reason = "runtime error";
 		break;
@@ -2377,6 +2380,21 @@ struct bpf_struct_ops bpf_sched_ext_ops = {
 	.name = "sched_ext_ops",
 };
 
+static void sysrq_handle_sched_ext_reset(int key)
+{
+	if (scx_ops_helper)
+		scx_ops_disable(SCX_EXIT_SYSRQ);
+	else
+		pr_info("sched_ext: BPF scheduler not yet used\n");
+}
+
+static const struct sysrq_key_op sysrq_sched_ext_reset_op = {
+	.handler	= sysrq_handle_sched_ext_reset,
+	.help_msg	= "reset-sched-ext(S)",
+	.action_msg	= "Disable sched_ext and revert all tasks to CFS",
+	.enable_mask	= SYSRQ_ENABLE_RTNICE,
+};
+
 void __init init_sched_ext_class(void)
 {
 	int cpu;
@@ -2400,6 +2418,8 @@ void __init init_sched_ext_class(void)
 		init_dsq(&rq->scx.local_dsq, SCX_DSQ_LOCAL);
 		rq->scx.nr_running = 0;
 	}
+
+	register_sysrq_key('S', &sysrq_sched_ext_reset_op);
 }
 
 
-- 
2.38.1