Ravi reported that the bpf_perf_link_attach() usage of
perf_event_set_bpf_prog() is not serialized by ctx->mutex, unlike the
PERF_EVENT_IOC_SET_BPF case.

Reported-by: Ravi Bangoria <ravi.bangoria@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 kernel/events/core.c |   34 ++++++++++++++++++++++++++++++----
 1 file changed, 30 insertions(+), 4 deletions(-)

--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6087,6 +6087,9 @@ static int perf_event_set_output(struct
 static int perf_event_set_filter(struct perf_event *event, void __user *arg);
 static int perf_copy_attr(struct perf_event_attr __user *uattr,
 			  struct perf_event_attr *attr);
+static int __perf_event_set_bpf_prog(struct perf_event *event,
+				     struct bpf_prog *prog,
+				     u64 bpf_cookie);
 
 static long _perf_ioctl(struct perf_event *event, unsigned int cmd, unsigned long arg)
 {
@@ -6149,7 +6152,7 @@ static long _perf_ioctl(struct perf_even
 		if (IS_ERR(prog))
 			return PTR_ERR(prog);
 
-		err = perf_event_set_bpf_prog(event, prog, 0);
+		err = __perf_event_set_bpf_prog(event, prog, 0);
 		if (err) {
 			bpf_prog_put(prog);
 			return err;
@@ -10875,8 +10878,9 @@ static inline bool perf_event_is_tracing
 	return false;
 }
 
-int perf_event_set_bpf_prog(struct perf_event *event, struct bpf_prog *prog,
-			    u64 bpf_cookie)
+static int __perf_event_set_bpf_prog(struct perf_event *event,
+				     struct bpf_prog *prog,
+				     u64 bpf_cookie)
 {
 	bool is_kprobe, is_uprobe, is_tracepoint, is_syscall_tp;
 
@@ -10914,6 +10918,20 @@ int perf_event_set_bpf_prog(struct perf_
 	return perf_event_attach_bpf_prog(event, prog, bpf_cookie);
 }
 
+int perf_event_set_bpf_prog(struct perf_event *event,
+			    struct bpf_prog *prog,
+			    u64 bpf_cookie)
+{
+	struct perf_event_context *ctx;
+	int ret;
+
+	ctx = perf_event_ctx_lock(event);
+	ret = __perf_event_set_bpf_prog(event, prog, bpf_cookie);
+	perf_event_ctx_unlock(event, ctx);
+
+	return ret;
+}
+
 void perf_event_free_bpf_prog(struct perf_event *event)
 {
 	if (!event->prog)
@@ -10936,7 +10954,15 @@ static void perf_event_free_filter(struc
 {
 }
 
-int perf_event_set_bpf_prog(struct perf_event *event, struct bpf_prog *prog,
+static int __perf_event_set_bpf_prog(struct perf_event *event,
+				     struct bpf_prog *prog,
+				     u64 bpf_cookie)
+{
+	return -ENOENT;
+}
+
+int perf_event_set_bpf_prog(struct perf_event *event,
+			    struct bpf_prog *prog,
 			    u64 bpf_cookie)
 {
 	return -ENOENT;