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Date:   Tue, 21 Jul 2020 14:06:06 +0300
From:   Dmitry Yakunin <zeil@...dex-team.ru>
To:     Daniel Borkmann <daniel@...earbox.net>,
        "alexei.starovoitov@...il.com" <alexei.starovoitov@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>
Cc:     "sdf@...gle.com" <sdf@...gle.com>
Subject: Re: [PATCH bpf-next v3 4/4] bpf: try to use existing cgroup storage in bpf_prog_test_run_skb



16.07.2020, 23:19, "Daniel Borkmann" <daniel@...earbox.net>:
> On 7/15/20 9:51 PM, Dmitry Yakunin wrote:
>>  Now we cannot check results in cgroup storage after running
>>  BPF_PROG_TEST_RUN command because it allocates dummy cgroup storage
>>  during test. This patch implements simple logic for searching already
>>  allocated cgroup storage through iterating effective programs of current
>>  cgroup and finding the first match. If match is not found fallback to
>>  temporary storage is happened.
>>
>>  v2:
>>     - fix build without CONFIG_CGROUP_BPF (kernel test robot <lkp@...el.com>)
>>
>>  Signed-off-by: Dmitry Yakunin <zeil@...dex-team.ru>
>>  ---
>>    net/bpf/test_run.c | 64 +++++++++++++++++-
>>    .../selftests/bpf/prog_tests/cgroup_skb_prog_run.c | 78 ++++++++++++++++++++++
>>    2 files changed, 139 insertions(+), 3 deletions(-)
>>    create mode 100644 tools/testing/selftests/bpf/prog_tests/cgroup_skb_prog_run.c
>>
>>  diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
>>  index 050390d..7382b22 100644
>>  --- a/net/bpf/test_run.c
>>  +++ b/net/bpf/test_run.c
>>  @@ -15,15 +15,67 @@
>>    #define CREATE_TRACE_POINTS
>>    #include <trace/events/bpf_test_run.h>
>>
>>  +#ifdef CONFIG_CGROUP_BPF
>>  +
>>  +static struct bpf_prog_array_item *bpf_prog_find_active(struct bpf_prog *prog,
>>  + struct bpf_prog_array *effective)
>>  +{
>>  + struct bpf_prog_array_item *item;
>>  + struct bpf_prog_array *array;
>>  + struct bpf_prog *p;
>>  +
>>  + array = rcu_dereference(effective);
>>  + if (!array)
>>  + return NULL;
>>  +
>>  + item = &array->items[0];
>>  + while ((p = READ_ONCE(item->prog))) {
>>  + if (p == prog)
>>  + return item;
>>  + item++;
>>  + }
>>  +
>>  + return NULL;
>>  +}
>>  +
>>  +static struct bpf_cgroup_storage **bpf_prog_find_active_storage(struct bpf_prog *prog)
>>  +{
>>  + struct bpf_prog_array_item *item;
>>  + struct cgroup *cgrp;
>>  +
>>  + if (prog->type != BPF_PROG_TYPE_CGROUP_SKB)
>>  + return NULL;
>>  +
>>  + cgrp = task_dfl_cgroup(current);
>>  +
>>  + item = bpf_prog_find_active(prog,
>>  + cgrp->bpf.effective[BPF_CGROUP_INET_INGRESS]);
>>  + if (!item)
>>  + item = bpf_prog_find_active(prog,
>>  + cgrp->bpf.effective[BPF_CGROUP_INET_EGRESS]);
>>  +
>>  + return item ? item->cgroup_storage : NULL;
>>  +}
>>  +
>>  +#else
>>  +
>>  +static struct bpf_cgroup_storage **bpf_prog_find_active_storage(struct bpf_prog *prog)
>>  +{
>>  + return NULL;
>>  +}
>>  +
>>  +#endif
>>  +
>>    static int bpf_test_run(struct bpf_prog *prog, void *ctx, u32 repeat,
>>                            u32 *retval, u32 *time, bool xdp)
>>    {
>>  - struct bpf_cgroup_storage *storage[MAX_BPF_CGROUP_STORAGE_TYPE] = { NULL };
>>  + struct bpf_cgroup_storage *dummy_storage[MAX_BPF_CGROUP_STORAGE_TYPE] = { NULL };
>>  + struct bpf_cgroup_storage **storage = dummy_storage;
>>            u64 time_start, time_spent = 0;
>>            int ret = 0;
>>            u32 i;
>>
>>  - ret = bpf_cgroup_storages_alloc(storage, prog);
>>  + ret = bpf_cgroup_storages_alloc(dummy_storage, prog);
>>            if (ret)
>>                    return ret;
>>
>>  @@ -31,6 +83,9 @@ static int bpf_test_run(struct bpf_prog *prog, void *ctx, u32 repeat,
>>                    repeat = 1;
>>
>>            rcu_read_lock();
>>  + storage = bpf_prog_find_active_storage(prog);
>>  + if (!storage)
>>  + storage = dummy_storage;
>>            migrate_disable();
>>            time_start = ktime_get_ns();
>>            for (i = 0; i < repeat; i++) {
>>  @@ -54,6 +109,9 @@ static int bpf_test_run(struct bpf_prog *prog, void *ctx, u32 repeat,
>>                            cond_resched();
>>
>>                            rcu_read_lock();
>>  + storage = bpf_prog_find_active_storage(prog);
>>  + if (!storage)
>>  + storage = dummy_storage;
>>                            migrate_disable();
>>                            time_start = ktime_get_ns();
>>                    }
>>  @@ -65,7 +123,7 @@ static int bpf_test_run(struct bpf_prog *prog, void *ctx, u32 repeat,
>>            do_div(time_spent, repeat);
>>            *time = time_spent > U32_MAX ? U32_MAX : (u32)time_spent;
>>
>>  - bpf_cgroup_storages_free(storage);
>>  + bpf_cgroup_storages_free(dummy_storage);
>>
>>            return ret;
>>    }
>>  diff --git a/tools/testing/selftests/bpf/prog_tests/cgroup_skb_prog_run.c b/tools/testing/selftests/bpf/prog_tests/cgroup_skb_prog_run.c
>>  new file mode 100644
>>  index 0000000..12ca881
>>  --- /dev/null
>>  +++ b/tools/testing/selftests/bpf/prog_tests/cgroup_skb_prog_run.c
>>  @@ -0,0 +1,78 @@
>>  +// SPDX-License-Identifier: GPL-2.0
>>  +
>>  +#include <test_progs.h>
>>  +
>>  +#include "cgroup_helpers.h"
>>  +#include "network_helpers.h"
>>  +
>>  +static char bpf_log_buf[BPF_LOG_BUF_SIZE];
>>  +
>>  +void test_cgroup_skb_prog_run(void)
>>  +{
>>  + struct bpf_insn prog[] = {
>>  + BPF_LD_MAP_FD(BPF_REG_1, 0), /* map fd */
>>  + BPF_MOV64_IMM(BPF_REG_2, 0), /* flags, not used */
>>  + BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_get_local_storage),
>>  + BPF_MOV64_IMM(BPF_REG_1, 1),
>>  + BPF_RAW_INSN(BPF_STX | BPF_XADD | BPF_W, BPF_REG_0, BPF_REG_1, 0, 0),
>>  +
>>  + BPF_MOV64_IMM(BPF_REG_0, 1), /* r0 = 1 */
>>  + BPF_EXIT_INSN(),
>>  + };
>>  + size_t insns_cnt = sizeof(prog) / sizeof(struct bpf_insn);
>>  + int storage_fd = -1, prog_fd = -1, cg_fd = -1;
>>  + struct bpf_cgroup_storage_key key;
>>  + __u32 duration, retval, size;
>>  + char buf[128];
>>  + __u64 value;
>>  + int err;
>>  +
>>  + storage_fd = bpf_create_map(BPF_MAP_TYPE_CGROUP_STORAGE,
>>  + sizeof(struct bpf_cgroup_storage_key),
>>  + 8, 0, 0);
>>  + if (CHECK(storage_fd < 0, "create_map", "%s\n", strerror(errno)))
>>  + goto out;
>>  +
>>  + prog[0].imm = storage_fd;
>>  +
>>  + prog_fd = bpf_load_program(BPF_PROG_TYPE_CGROUP_SKB,
>>  + prog, insns_cnt, "GPL", 0,
>>  + bpf_log_buf, BPF_LOG_BUF_SIZE);
>>  + if (CHECK(prog_fd < 0, "prog_load",
>>  + "verifier output:\n%s\n-------\n", bpf_log_buf))
>>  + goto out;
>>  +
>>  + if (CHECK_FAIL(setup_cgroup_environment()))
>>  + goto out;
>>  +
>>  + cg_fd = create_and_get_cgroup("/cg");
>>  + if (CHECK_FAIL(cg_fd < 0))
>>  + goto out;
>>  +
>>  + if (CHECK_FAIL(join_cgroup("/cg")))
>>  + goto out;
>>  +
>>  + if (CHECK(bpf_prog_attach(prog_fd, cg_fd, BPF_CGROUP_INET_EGRESS, 0),
>>  + "prog_attach", "%s\n", strerror(errno)))
>>  + goto out;
>>  +
>>  + err = bpf_prog_test_run(prog_fd, NUM_ITER, &pkt_v4, sizeof(pkt_v4),
>>  + buf, &size, &retval, &duration);
>
> Hm, I think this approach is rather suboptimal, meaning, you need to load & even
> actively attach the test program also to the cgroup aside from pushing this via
> BPF prog test infra. So any other potential background traffic egressing from the
> application will also go through the test program via BPF_CGROUP_INET_EGRESS.
> Can't we instead extend the test infra to prepopulate and fetch the content from
> the temp storage instead so this does not have any other side-effects?

Thanks for you response, Daniel! Yes, I forgot to mention that this change can affect existing storage values if we run PROG_TEST_RUN command on the online program. But I thought that the case of testing bpf programs on production environments is uncommon and such solution is acceptable trade-off. I see potential rework of this patch through extending bpf_attr for PROG_TEST_RUN with user pointer to memory for cgroup storage contents and dumping cgroup storage with lookup_batch callback after test ends. Does this solution sounds good for you?

>>  + CHECK(err || retval != 1, "prog_test_run",
>>  + "err %d errno %d retval %d\n", err, errno, retval);
>>  +
>>  + /* check that cgroup storage results are available after test run */
>>  +
>>  + err = bpf_map_get_next_key(storage_fd, NULL, &key);
>>  + CHECK(err, "map_get_next_key", "%s\n", strerror(errno));
>>  +
>>  + err = bpf_map_lookup_elem(storage_fd, &key, &value);
>>  + CHECK(err || value != NUM_ITER,
>>  + "map_lookup_elem",
>>  + "err %d errno %d cnt %lld(%d)\n", err, errno, value, NUM_ITER);
>>  +out:
>>  + close(storage_fd);
>>  + close(prog_fd);
>>  + close(cg_fd);
>>  + cleanup_cgroup_environment();
>>  +}

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