Commit 1f243622 authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Daniel Borkmann

selftests/bpf: Fix ringbuf selftest sample counting undeterminism

Fix test race, in which background poll can get either 5 or 6 samples,
depending on timing of notification. Prevent this by open-coding sample
triggering and forcing notification for the very last sample only.

Also switch to using atomic increments and exchanges for more obviously
reliable counting and checking. Additionally, check expected processed sample
counters for single-threaded use cases as well.

Fixes: 9a5f25ad ("selftests/bpf: Fix sample_cnt shared between two threads")
Signed-off-by: default avatarAndrii Nakryiko <andriin@fb.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20200608003615.3549991-1-andriin@fb.com
parent e7ed83d6
...@@ -25,13 +25,23 @@ struct sample { ...@@ -25,13 +25,23 @@ struct sample {
char comm[16]; char comm[16];
}; };
static volatile int sample_cnt; static int sample_cnt;
static void atomic_inc(int *cnt)
{
__atomic_add_fetch(cnt, 1, __ATOMIC_SEQ_CST);
}
static int atomic_xchg(int *cnt, int val)
{
return __atomic_exchange_n(cnt, val, __ATOMIC_SEQ_CST);
}
static int process_sample(void *ctx, void *data, size_t len) static int process_sample(void *ctx, void *data, size_t len)
{ {
struct sample *s = data; struct sample *s = data;
sample_cnt++; atomic_inc(&sample_cnt);
switch (s->seq) { switch (s->seq) {
case 0: case 0:
...@@ -76,7 +86,7 @@ void test_ringbuf(void) ...@@ -76,7 +86,7 @@ void test_ringbuf(void)
const size_t rec_sz = BPF_RINGBUF_HDR_SZ + sizeof(struct sample); const size_t rec_sz = BPF_RINGBUF_HDR_SZ + sizeof(struct sample);
pthread_t thread; pthread_t thread;
long bg_ret = -1; long bg_ret = -1;
int err; int err, cnt;
skel = test_ringbuf__open_and_load(); skel = test_ringbuf__open_and_load();
if (CHECK(!skel, "skel_open_load", "skeleton open&load failed\n")) if (CHECK(!skel, "skel_open_load", "skeleton open&load failed\n"))
...@@ -116,11 +126,15 @@ void test_ringbuf(void) ...@@ -116,11 +126,15 @@ void test_ringbuf(void)
/* -EDONE is used as an indicator that we are done */ /* -EDONE is used as an indicator that we are done */
if (CHECK(err != -EDONE, "err_done", "done err: %d\n", err)) if (CHECK(err != -EDONE, "err_done", "done err: %d\n", err))
goto cleanup; goto cleanup;
cnt = atomic_xchg(&sample_cnt, 0);
CHECK(cnt != 2, "cnt", "exp %d samples, got %d\n", 2, cnt);
/* we expect extra polling to return nothing */ /* we expect extra polling to return nothing */
err = ring_buffer__poll(ringbuf, 0); err = ring_buffer__poll(ringbuf, 0);
if (CHECK(err != 0, "extra_samples", "poll result: %d\n", err)) if (CHECK(err != 0, "extra_samples", "poll result: %d\n", err))
goto cleanup; goto cleanup;
cnt = atomic_xchg(&sample_cnt, 0);
CHECK(cnt != 0, "cnt", "exp %d samples, got %d\n", 0, cnt);
CHECK(skel->bss->dropped != 0, "err_dropped", "exp %ld, got %ld\n", CHECK(skel->bss->dropped != 0, "err_dropped", "exp %ld, got %ld\n",
0L, skel->bss->dropped); 0L, skel->bss->dropped);
...@@ -136,6 +150,8 @@ void test_ringbuf(void) ...@@ -136,6 +150,8 @@ void test_ringbuf(void)
3L * rec_sz, skel->bss->cons_pos); 3L * rec_sz, skel->bss->cons_pos);
err = ring_buffer__poll(ringbuf, -1); err = ring_buffer__poll(ringbuf, -1);
CHECK(err <= 0, "poll_err", "err %d\n", err); CHECK(err <= 0, "poll_err", "err %d\n", err);
cnt = atomic_xchg(&sample_cnt, 0);
CHECK(cnt != 2, "cnt", "exp %d samples, got %d\n", 2, cnt);
/* start poll in background w/ long timeout */ /* start poll in background w/ long timeout */
err = pthread_create(&thread, NULL, poll_thread, (void *)(long)10000); err = pthread_create(&thread, NULL, poll_thread, (void *)(long)10000);
...@@ -164,6 +180,8 @@ void test_ringbuf(void) ...@@ -164,6 +180,8 @@ void test_ringbuf(void)
2L, skel->bss->total); 2L, skel->bss->total);
CHECK(skel->bss->discarded != 1, "err_discarded", "exp %ld, got %ld\n", CHECK(skel->bss->discarded != 1, "err_discarded", "exp %ld, got %ld\n",
1L, skel->bss->discarded); 1L, skel->bss->discarded);
cnt = atomic_xchg(&sample_cnt, 0);
CHECK(cnt != 0, "cnt", "exp %d samples, got %d\n", 0, cnt);
/* clear flags to return to "adaptive" notification mode */ /* clear flags to return to "adaptive" notification mode */
skel->bss->flags = 0; skel->bss->flags = 0;
...@@ -178,10 +196,20 @@ void test_ringbuf(void) ...@@ -178,10 +196,20 @@ void test_ringbuf(void)
if (CHECK(err != EBUSY, "try_join", "err %d\n", err)) if (CHECK(err != EBUSY, "try_join", "err %d\n", err))
goto cleanup; goto cleanup;
/* still no samples, because consumer is behind */
cnt = atomic_xchg(&sample_cnt, 0);
CHECK(cnt != 0, "cnt", "exp %d samples, got %d\n", 0, cnt);
skel->bss->dropped = 0;
skel->bss->total = 0;
skel->bss->discarded = 0;
skel->bss->value = 333;
syscall(__NR_getpgid);
/* now force notifications */ /* now force notifications */
skel->bss->flags = BPF_RB_FORCE_WAKEUP; skel->bss->flags = BPF_RB_FORCE_WAKEUP;
sample_cnt = 0; skel->bss->value = 777;
trigger_samples(); syscall(__NR_getpgid);
/* now we should get a pending notification */ /* now we should get a pending notification */
usleep(50000); usleep(50000);
...@@ -193,8 +221,8 @@ void test_ringbuf(void) ...@@ -193,8 +221,8 @@ void test_ringbuf(void)
goto cleanup; goto cleanup;
/* 3 rounds, 2 samples each */ /* 3 rounds, 2 samples each */
CHECK(sample_cnt != 6, "wrong_sample_cnt", cnt = atomic_xchg(&sample_cnt, 0);
"expected to see %d samples, got %d\n", 6, sample_cnt); CHECK(cnt != 6, "cnt", "exp %d samples, got %d\n", 6, cnt);
/* BPF side did everything right */ /* BPF side did everything right */
CHECK(skel->bss->dropped != 0, "err_dropped", "exp %ld, got %ld\n", CHECK(skel->bss->dropped != 0, "err_dropped", "exp %ld, got %ld\n",
......
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