[PATCH 16/39] sched_ext: Add sysrq-S which disables the BPF scheduler

Tejun Heo
2024-05-01T15:13:50Z

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 +
kernel/sched/build_policy.c | 1 +
kernel/sched/ext.c | 20 ++++++++++++++++++++
3 files changed, 22 insertions(+)

diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index 02217e3c916b..1ce3535cba6d 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/kernel/sched/build_policy.c b/kernel/sched/build_policy.c
index 2a2f10367ceb..e0e73b44afe9 100644
--- a/kernel/sched/build_policy.c
+++ b/kernel/sched/build_policy.c
@@ -31,6 +31,7 @@
#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 d4f52209111f..e017b79aa1e7 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -20,6 +20,7 @@ enum scx_exit_kind {
SCX_EXIT_UNREG = 64, /* user-space initiated unregistration */
SCX_EXIT_UNREG_BPF, /* BPF-initiated unregistration */
SCX_EXIT_UNREG_KERN, /* kernel-initiated 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() */
@@ -2767,6 +2768,8 @@ static const char *scx_exit_reason(enum scx_exit_kind kind)
return "Scheduler unregistered from BPF";
case SCX_EXIT_UNREG_KERN:
return "Scheduler unregistered from the main kernel";
+ case SCX_EXIT_SYSRQ:
+ return "disabled by sysrq-S";
case SCX_EXIT_ERROR:
return "runtime error";
case SCX_EXIT_ERROR_BPF:
@@ -3506,6 +3509,21 @@ static struct bpf_struct_ops bpf_sched_ext_ops = {
* System integration and init.
*/

+static void sysrq_handle_sched_ext_reset(u8 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)
{
s32 cpu, v;
@@ -3529,6 +3547,8 @@ void __init init_sched_ext_class(void)
init_dsq(&rq->scx.local_dsq, SCX_DSQ_LOCAL);
INIT_LIST_HEAD(&rq->scx.runnable_list);
}
+
+ register_sysrq_key('S', &sysrq_sched_ext_reset_op);
}

--
2.44.0