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Date: Tue, 22 Dec 2020 23:58:31 +0000 From: Song Liu <songliubraving@...com> To: Andrii Nakryiko <andrii@...nel.org> CC: bpf <bpf@...r.kernel.org>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, Alexei Starovoitov <ast@...com>, "daniel@...earbox.net" <daniel@...earbox.net>, Kernel Team <Kernel-team@...com> Subject: Re: [PATCH bpf] selftests/bpf: work-around EBUSY errors from hashmap update/delete > On Dec 22, 2020, at 11:53 AM, Andrii Nakryiko <andrii@...nel.org> wrote: > > 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@...com> > Signed-off-by: Andrii Nakryiko <andrii@...nel.org> Thanks for the fix! Acked-by: Song Liu <songliubraving@...com> With one minor nitpick below > --- > 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 [...] > + 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); nit: Why 5 here vs. 20 above? > + if (err) > + printf("error %d %d\n", err, errno); > + assert(err == 0); > } > } > } > -- > 2.24.1 >
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