20b6cc34ea74 ("bpf: Avoid hashtab deadlock with map_locked") introduced
a possibility of getting EBUSY error on lock contention, which seems to happen
very deterministically in test_maps when running 1024 threads on low-CPU
machine. In libbpf CI case, it's a 2 CPU VM and it's hitting this 100% of the
time. Work around by retrying on EBUSY (and EAGAIN, while we are at it) after
a small sleep. sched_yield() is too agressive and fails even after 20 retries,
so I went with usleep(1) for backoff.
Also log actual error returned to make it easier to see what's going on.
Fixes: 20b6cc34ea74 ("bpf: Avoid hashtab deadlock with map_locked")
Cc: Song Liu <songliubraving@xxxxxx>
Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
---
tools/testing/selftests/bpf/test_maps.c | 46 +++++++++++++++++++++----
1 file changed, 40 insertions(+), 6 deletions(-)
diff --git a/tools/testing/selftests/bpf/test_maps.c b/tools/testing/selftests/bpf/test_maps.c
index 0ad3e6305ff0..809004f4995f 100644
--- a/tools/testing/selftests/bpf/test_maps.c
+++ b/tools/testing/selftests/bpf/test_maps.c
@@ -1312,22 +1312,56 @@ static void test_map_stress(void)
#define DO_UPDATE 1
#define DO_DELETE 0
+static int map_update_retriable(int map_fd, const void *key, const void *value,
+ int flags, int attempts)
+{
+ while (bpf_map_update_elem(map_fd, key, value, flags)) {
+ if (!attempts || (errno != EAGAIN && errno != EBUSY))
+ return -errno;
+
+ usleep(1);
+ attempts--;
+ }
+
+ return 0;
+}
+
+static int map_delete_retriable(int map_fd, const void *key, int attempts)
+{
+ while (bpf_map_delete_elem(map_fd, key)) {
+ if (!attempts || (errno != EAGAIN && errno != EBUSY))
+ return -errno;
+
+ usleep(1);
+ attempts--;
+ }
+
+ return 0;
+}
+
static void test_update_delete(unsigned int fn, void *data)
{
int do_update = ((int *)data)[1];
int fd = ((int *)data)[0];
- int i, key, value;
+ int i, key, value, err;
for (i = fn; i < MAP_SIZE; i += TASKS) {
key = value = i;
if (do_update) {
- assert(bpf_map_update_elem(fd, &key, &value,
- BPF_NOEXIST) == 0);
- assert(bpf_map_update_elem(fd, &key, &value,
- BPF_EXIST) == 0);
+ err = map_update_retriable(fd, &key, &value, BPF_NOEXIST, 20);
+ if (err)
+ printf("error %d %d\n", err, errno);
+ assert(err == 0);
+ err = map_update_retriable(fd, &key, &value, BPF_EXIST, 20);
+ if (err)
+ printf("error %d %d\n", err, errno);
+ assert(err == 0);
} else {
- assert(bpf_map_delete_elem(fd, &key) == 0);
+ err = map_delete_retriable(fd, &key, 5);
+ if (err)
+ printf("error %d %d\n", err, errno);
+ assert(err == 0);
}
}
}
--
2.24.1
