From: Andrii Nakryiko andrii@kernel.org
mainline inclusion from mainline-5.11-rc3 commit 11b844b0b7c7c3dc8e8f4d0bbaad5e798351862c category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I5EUVD CVE: NA
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
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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") Signed-off-by: Andrii Nakryiko andrii@kernel.org Signed-off-by: Daniel Borkmann daniel@iogearbox.net Acked-by: Song Liu songliubraving@fb.com Link: https://lore.kernel.org/bpf/20201223200652.3417075-1-andrii@kernel.org (cherry picked from commit 11b844b0b7c7c3dc8e8f4d0bbaad5e798351862c) Signed-off-by: Wang Yufen wangyufen@huawei.com --- tools/testing/selftests/bpf/test_maps.c | 48 +++++++++++++++++++++---- 1 file changed, 42 insertions(+), 6 deletions(-)
diff --git a/tools/testing/selftests/bpf/test_maps.c b/tools/testing/selftests/bpf/test_maps.c index 179e680e8d13..20eb7301850e 100644 --- a/tools/testing/selftests/bpf/test_maps.c +++ b/tools/testing/selftests/bpf/test_maps.c @@ -1311,22 +1311,58 @@ static void test_map_stress(void) #define DO_UPDATE 1 #define DO_DELETE 0
+#define MAP_RETRIES 20 + +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, MAP_RETRIES); + if (err) + printf("error %d %d\n", err, errno); + assert(err == 0); + err = map_update_retriable(fd, &key, &value, BPF_EXIST, MAP_RETRIES); + 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, MAP_RETRIES); + if (err) + printf("error %d %d\n", err, errno); + assert(err == 0); } } }