bpf: sched: introduce bpf_sched_enable()

maillist inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5F6X6
CVE: NA

Reference: https://lore.kernel.org/all/20210916162451.709260-1-guro@fb.com/

-------------------

Introduce a dedicated static key and the bpf_sched_enabled() wrapper
to guard all invocations of bpf programs in the scheduler code.

It will help to avoid any potential performance regression in a case
when no scheduler bpf programs are attached.
Signed-off-by: NRoman Gushchin <guro@fb.com>
Signed-off-by: NChen Hui <judy.chenhui@huawei.com>
Signed-off-by: NRen Zhijie <renzhijie2@huawei.com>

include/linux/bpf_sched.h

@@ -6,6 +6,8 @@
 
 #ifdef CONFIG_BPF_SCHED
 
+#include <linux/jump_label.h>
+
 #define BPF_SCHED_HOOK(RET, DEFAULT, NAME, ...) \
 	RET bpf_sched_##NAME(__VA_ARGS__);
 #include <linux/sched_hook_defs.h>
@@ -14,6 +16,23 @@
 int bpf_sched_verify_prog(struct bpf_verifier_log *vlog,
 			  const struct bpf_prog *prog);
 
+DECLARE_STATIC_KEY_FALSE(bpf_sched_enabled_key);
+
+static inline bool bpf_sched_enabled(void)
+{
+	return static_branch_unlikely(&bpf_sched_enabled_key);
+}
+
+static inline void bpf_sched_inc(void)
+{
+	static_branch_inc(&bpf_sched_enabled_key);
+}
+
+static inline void bpf_sched_dec(void)
+{
+	static_branch_dec(&bpf_sched_enabled_key);
+}
+
 #else /* !CONFIG_BPF_SCHED */
 
 static inline int bpf_sched_verify_prog(struct bpf_verifier_log *vlog,
@@ -22,5 +41,10 @@ static inline int bpf_sched_verify_prog(struct bpf_verifier_log *vlog,
 	return -EOPNOTSUPP;
 }
 
+static inline bool bpf_sched_enabled(void)
+{
+	return false;
+}
+
 #endif /* CONFIG_BPF_SCHED */
 #endif /* _LINUX_BPF_SCHED_H */

kernel/bpf/syscall.c

@@ -31,6 +31,7 @@
 #include <linux/poll.h>
 #include <linux/bpf-netns.h>
 #include <linux/rcupdate_trace.h>
+#include <linux/bpf_sched.h>
 
 #define IS_FD_ARRAY(map) ((map)->map_type == BPF_MAP_TYPE_PERF_EVENT_ARRAY || \
 			  (map)->map_type == BPF_MAP_TYPE_CGROUP_ARRAY || \
@@ -2531,6 +2532,11 @@ static void bpf_tracing_link_release(struct bpf_link *link)
 	struct bpf_tracing_link *tr_link =
 		container_of(link, struct bpf_tracing_link, link);
 
+#ifdef CONFIG_BPF_SCHED
+	if (link->prog->type == BPF_PROG_TYPE_SCHED)
+		bpf_sched_dec();
+#endif
+
 	WARN_ON_ONCE(bpf_trampoline_unlink_prog(link->prog,
 						tr_link->trampoline));
 
@@ -2718,6 +2724,11 @@ static int bpf_tracing_prog_attach(struct bpf_prog *prog,
 		goto out_unlock;
 	}
 
+#ifdef CONFIG_BPF_SCHED
+	if (prog->type == BPF_PROG_TYPE_SCHED)
+		bpf_sched_inc();
+#endif
+
 	link->tgt_prog = tgt_prog;
 	link->trampoline = tr;
 

kernel/sched/bpf_sched.c

@@ -6,6 +6,8 @@
 #include <linux/btf_ids.h>
 #include "sched.h"
 
+DEFINE_STATIC_KEY_FALSE(bpf_sched_enabled_key);
+
 /*
  * For every hook declare a nop function where a BPF program can be attached.
  */