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From:   jinshan.xiong@gmail.com
To:     linux-kernel@vger.kernel.org, rostedt@goodmis.org, mingo@redhat.com
Cc:     yhs@fb.com, jinshan.xiong@uber.com,
        Jinshan Xiong <jinshan.xiong@gmail.com>
Subject: [PATCH] staging: tracing/kprobe: filter kprobe based perf event
Date:   Tue, 17 Sep 2019 22:24:06 -0700
Message-Id: <20190918052406.21385-1-jinshan.xiong@gmail.com>
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From: Jinshan Xiong <jinshan.xiong@gmail.com>

Invoking bpf program only if kprobe based perf_event has been added into
the percpu list. This is essential to make event tracing for cgroup to work
properly.

Signed-off-by: Jinshan Xiong <jinshan.xiong@gmail.com>
---
 kernel/trace/trace_kprobe.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 9d483ad9bb6c..40ef0f1945f7 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -1171,11 +1171,18 @@ static int
 kprobe_perf_func(struct trace_kprobe *tk, struct pt_regs *regs)
 {
 	struct trace_event_call *call = trace_probe_event_call(&tk->tp);
+	struct hlist_head *head = this_cpu_ptr(call->perf_events);
 	struct kprobe_trace_entry_head *entry;
-	struct hlist_head *head;
 	int size, __size, dsize;
 	int rctx;
 
+	/*
+	 * If head is empty, the process currently running on this cpu is not
+	 * interested by kprobe perf PMU.
+	 */
+	if (hlist_empty(head))
+		return 0;
+
 	if (bpf_prog_array_valid(call)) {
 		unsigned long orig_ip = instruction_pointer(regs);
 		int ret;
@@ -1193,10 +1200,6 @@ kprobe_perf_func(struct trace_kprobe *tk, struct pt_regs *regs)
 			return 0;
 	}
 
-	head = this_cpu_ptr(call->perf_events);
-	if (hlist_empty(head))
-		return 0;
-
 	dsize = __get_data_size(&tk->tp, regs);
 	__size = sizeof(*entry) + tk->tp.size + dsize;
 	size = ALIGN(__size + sizeof(u32), sizeof(u64));