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Wed, 08 Jun 2022 02:57:51 -0700 (PDT) Received: from krava ([193.85.244.190]) by smtp.gmail.com with ESMTPSA id m3-20020a05600c3b0300b003942a244f2fsm28377154wms.8.2022.06.08.02.57.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 08 Jun 2022 02:57:50 -0700 (PDT) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Wed, 8 Jun 2022 11:57:48 +0200 To: Alexei Starovoitov , Steven Rostedt Cc: Jiri Olsa , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Network Development , bpf , lkml , Martin KaFai Lau , Song Liu , Yonghong Song , John Fastabend , KP Singh , Masami Hiramatsu Subject: Re: [PATCHv2 bpf 3/3] bpf: Force cookies array to follow symbols sorting Message-ID: References: <20220606184731.437300-1-jolsa@kernel.org> <20220606184731.437300-4-jolsa@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Wed, Jun 08, 2022 at 09:59:41AM +0200, Jiri Olsa wrote: > On Tue, Jun 07, 2022 at 09:10:32PM -0700, Alexei Starovoitov wrote: > > On Tue, Jun 7, 2022 at 12:56 PM Jiri Olsa wrote: > > > > > > On Tue, Jun 07, 2022 at 11:40:47AM -0700, Alexei Starovoitov wrote: > > > > On Mon, Jun 6, 2022 at 11:48 AM Jiri Olsa wrote: > > > > > > > > > > When user specifies symbols and cookies for kprobe_multi link > > > > > interface it's very likely the cookies will be misplaced and > > > > > returned to wrong functions (via get_attach_cookie helper). > > > > > > > > > > The reason is that to resolve the provided functions we sort > > > > > them before passing them to ftrace_lookup_symbols, but we do > > > > > not do the same sort on the cookie values. > > > > > > > > > > Fixing this by using sort_r function with custom swap callback > > > > > that swaps cookie values as well. > > > > > > > > > > Fixes: 0236fec57a15 ("bpf: Resolve symbols with ftrace_lookup_symbols for kprobe multi link") > > > > > Signed-off-by: Jiri Olsa > > > > > > > > It looks good, but something in this patch is causing a regression: > > > > ./test_progs -t kprobe_multi > > > > test_kprobe_multi_test:PASS:load_kallsyms 0 nsec > > > > #80/1 kprobe_multi_test/skel_api:OK > > > > #80/2 kprobe_multi_test/link_api_addrs:OK > > > > #80/3 kprobe_multi_test/link_api_syms:OK > > > > #80/4 kprobe_multi_test/attach_api_pattern:OK > > > > #80/5 kprobe_multi_test/attach_api_addrs:OK > > > > #80/6 kprobe_multi_test/attach_api_syms:OK > > > > #80/7 kprobe_multi_test/attach_api_fails:OK > > > > test_bench_attach:PASS:get_syms 0 nsec > > > > test_bench_attach:PASS:kprobe_multi_empty__open_and_load 0 nsec > > > > libbpf: prog 'test_kprobe_empty': failed to attach: No such process > > > > test_bench_attach:FAIL:bpf_program__attach_kprobe_multi_opts > > > > unexpected error: -3 > > > > #80/8 kprobe_multi_test/bench_attach:FAIL > > > > #80 kprobe_multi_test:FAIL > > > > > > looks like kallsyms search failed to find some symbol, > > > but I can't reproduce with: > > > > > > ./vmtest.sh -- ./test_progs -t kprobe_multi > > > > > > can you share .config you used? > > > > I don't think it's config related. > > Patch 2 is doing: > > > > - if (!bsearch(&name, args->syms, args->cnt, sizeof(*args->syms), symbols_cmp)) > > + sym = bsearch(&name, args->syms, args->cnt, sizeof(*args->syms), symbols_cmp); > > + if (!sym) > > + return 0; > > + > > + idx = sym - args->syms; > > + if (args->addrs[idx]) > > return 0; > > > > addr = ftrace_location(addr); > > if (!addr) > > return 0; > > > > - args->addrs[args->found++] = addr; > > + args->addrs[idx] = addr; > > + args->found++; > > return args->found == args->cnt ? 1 : 0; > > > > There are plenty of functions with the same name > > in available_filter_functions. > > So > > if (args->addrs[idx]) > > return 0; > > triggers for a lot of them. > > At the end args->found != args->cnt. > > there's code in get_syms (prog_tests/kprobe_multi_test.c) > that filters out duplicates > > > > > Here is trivial debug patch: > > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c > > index 601ccf1b2f09..c567cf56cb57 100644 > > --- a/kernel/trace/ftrace.c > > +++ b/kernel/trace/ftrace.c > > @@ -8037,8 +8037,10 @@ static int kallsyms_callback(void *data, const > > char *name, > > return 0; > > > > idx = sym - args->syms; > > - if (args->addrs[idx]) > > + if (args->addrs[idx]) { > > + printk("idx %x name %s\n", idx, name); > > return 0; > > + } > > > > addr = ftrace_location(addr); > > if (!addr) > > @@ -8078,6 +8080,7 @@ int ftrace_lookup_symbols(const char > > **sorted_syms, size_t cnt, unsigned long *a > > err = kallsyms_on_each_symbol(kallsyms_callback, &args); > > if (err < 0) > > return err; > > + printk("found %zd cnt %zd\n", args.found, args.cnt); > > return args.found == args.cnt ? 0 : -ESRCH; > > } > > > > [ 13.096160] idx a500 name unregister_vclock > > [ 13.096930] idx 82fb name pt_regs_offset > > [ 13.106969] idx 92be name set_root > > [ 13.107290] idx 4414 name event_function > > [ 13.112570] idx 7d1d name phy_init > > [ 13.114459] idx 7d13 name phy_exit > > [ 13.114777] idx ab91 name watchdog > > [ 13.115730] found 46921 cnt 47036 > > > > I don't understand how it works for you at all. > > It passes in BPF CI only because we don't run > > kprobe_multi_test/bench_attach there (yet). > > reproduced after I updated the tree today.. not sure why I did > not see that before, going to check ok, I'm not completely crazy ;-) it's the weak functions fix: b39181f7c690 ftrace: Add FTRACE_MCOUNT_MAX_OFFSET to avoid adding weak function I should have noticed this before (from changelog): A worker thread is added at boot up to scan all the ftrace record entries, and will mark any that fail the FTRACE_MCOUNT_MAX_OFFSET test as disabled. They will still appear in the available_filter_functions file as: __ftrace_invalid_address___ (showing the offset that caused it to be invalid). Steven, is there a reason to show '__ftrace_invalid_address___*' symbols in available_filter_functions? it seems more like debug message to me I can easily filter them out, but my assumption was that any symbol in available_filter_functions could be resolved in /proc/kalsyms with the workaround patch below the bench test is passing for me thanks, jirka --- diff --git a/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c b/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c index 586dc52d6fb9..88086ac23ef3 100644 --- a/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c +++ b/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c @@ -364,6 +364,8 @@ static int get_syms(char ***symsp, size_t *cntp) continue; if (!strncmp(name, "rcu_", 4)) continue; + if (!strncmp(name, "__ftrace_invalid_address__", sizeof("__ftrace_invalid_address__") - 1)) + continue; err = hashmap__add(map, name, NULL); if (err) { free(name);