From: Andrii Nakryiko <andriin@fb.com>
Date: Mon, 1 Jun 2020 22:03:49 -0700
Subject: selftests/bpf: Fix sample_cnt shared between two threads
Patch-mainline: v5.8-rc1
Git-commit: 9a5f25ad30e5bb40a2e0c61c991594d3e6529c0a
References: bsc#1177028

Make sample_cnt volatile to fix possible selftests failure due to compiler
optimization preventing latest sample_cnt value to be visible to main thread.
sample_cnt is incremented in background thread, which is then joined into main
thread. So in terms of visibility sample_cnt update is ok. But because it's
not volatile, compiler might make optimizations that would prevent main thread
to see latest updated value. Fix this by marking global variable volatile.

Fixes: cb1c9ddd5525 ("selftests/bpf: Add BPF ringbuf selftests")
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20200602050349.215037-1-andriin@fb.com
Acked-by: Gary Lin <glin@suse.com>
---
 tools/testing/selftests/bpf/prog_tests/ringbuf.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/tools/testing/selftests/bpf/prog_tests/ringbuf.c
+++ b/tools/testing/selftests/bpf/prog_tests/ringbuf.c
@@ -25,7 +25,7 @@ struct sample {
 	char comm[16];
 };
 
-static int sample_cnt;
+static volatile int sample_cnt;
 
 static int process_sample(void *ctx, void *data, size_t len)
 {