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b=Mu7jwEoZ38Y5+VbAL83S0PJ4vSJFTlIpCpdtkU/w5EHrgh2gtDCd15rTiewA2R8vV 7eZT3lVHhDElc57/n/LcStn1UuHfpfwpIgXdC3lpa0fCkDqgjhKUghDuWhZaQJPoB2 OcY7hP01Xp2+XCHLEgPk9RzM9hWud0rOITVjXIH12k1aG2WgEHOaCWkoUKoIPWdS+S E2G+r5Jqm6RhSP5c204p8+oapHfr2hzd+34ubut1dDzQLXMjGQdIrglyMR0O46MK/s mzvAx1UNFwmZaeobkb5Ny6LK6qErIVtlvMVh8CjN+c3ibaOOkLy00/uSQ81Ytshtj+ fU2rMhdIcp+RA== Date: Sun, 29 Sep 2024 19:18:08 -0700 From: Namhyung Kim To: Hyeonggon Yoo <42.hyeyoo@gmail.com> Cc: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Song Liu , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , LKML , bpf@vger.kernel.org, Andrew Morton , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Vlastimil Babka , Roman Gushchin , linux-mm@kvack.org, Arnaldo Carvalho de Melo Subject: Re: [RFC/PATCH bpf-next 3/3] selftests/bpf: Add a test for kmem_cache_iter Message-ID: References: <20240927184133.968283-1-namhyung@kernel.org> <20240927184133.968283-4-namhyung@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Stat-Signature: w4pq7p31bmyipadt5zzdgh5zb7uze15a X-Rspamd-Queue-Id: 0A3B41A0004 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1727662691-547670 X-HE-Meta: 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 FMMmE8/8 IRITrs6gS3yGLde8175GiUrI8OBTiYHa+lTx0EGdDmK9Kpr6iCpMb8Aab7xq8+wHbK0iHg5lhF+btGgDqTubVXoAtaLXrE2v4qbhGg4uayI4ge5zChv8oH4O6RNj9dQo2yNEiwBlcH0WTjJQF1P+BSf0aksxsI3qAIcycEVNEcb1D+EXjaSgJqpV0cJ+KKwzymXZjaVL8E9WI7SBKL6RjhQEKlrnud7zpQelYvzHebdivGFgXiVcaxoEgyqQBKMciApBS8M7R/mIdPlZNTn1RmdBc66vkEYX7YkKICmDJyRtuCnfZmhZWLJeS0DM8P/wydzYTZuOiej9aRtITSwbyrRqrj1oYtayht9d81K6T/zZGlQAqnOQelmg7CJxVY3/mAyzmX4u6ThRu9QT7SMi1RCLAMAXjZ8eAX1ey X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hello Hyeonggon, On Sun, Sep 29, 2024 at 11:27:25PM +0900, Hyeonggon Yoo wrote: > On Sun, Sep 29, 2024 at 3:13 PM Namhyung Kim wrote: > > > > On Fri, Sep 27, 2024 at 11:41:33AM -0700, Namhyung Kim wrote: > > > The test traverses all slab caches using the kmem_cache_iter and check > > > if current task's pointer is from "task_struct" slab cache. > > > > > > Signed-off-by: Namhyung Kim > > > --- > > > .../bpf/prog_tests/kmem_cache_iter.c | 64 ++++++++++++++++++ > > > tools/testing/selftests/bpf/progs/bpf_iter.h | 7 ++ > > > .../selftests/bpf/progs/kmem_cache_iter.c | 66 +++++++++++++++++++ > > > 3 files changed, 137 insertions(+) > > > create mode 100644 tools/testing/selftests/bpf/prog_tests/kmem_cache_iter.c > > > create mode 100644 tools/testing/selftests/bpf/progs/kmem_cache_iter.c > > > > > > diff --git a/tools/testing/selftests/bpf/prog_tests/kmem_cache_iter.c b/tools/testing/selftests/bpf/prog_tests/kmem_cache_iter.c > > > new file mode 100644 > > > index 0000000000000000..814bcc453e9f3ccd > > > --- /dev/null > > > +++ b/tools/testing/selftests/bpf/prog_tests/kmem_cache_iter.c > > > @@ -0,0 +1,64 @@ > > > +// SPDX-License-Identifier: GPL-2.0 > > > +/* Copyright (c) 2024 Google */ > > > + > > > +#include > > > +#include > > > +#include > > > +#include "kmem_cache_iter.skel.h" > > > + > > > +static void test_kmem_cache_iter_check_task(struct kmem_cache_iter *skel) > > > +{ > > > + LIBBPF_OPTS(bpf_test_run_opts, opts, > > > + .flags = BPF_F_TEST_RUN_ON_CPU, > > > + ); > > > + int prog_fd = bpf_program__fd(skel->progs.check_task_struct); > > > + > > > + /* get task_struct and check it if's from a slab cache */ > > > + bpf_prog_test_run_opts(prog_fd, &opts); > > > + > > > + /* the BPF program should set 'found' variable */ > > > + ASSERT_EQ(skel->bss->found, 1, "found task_struct"); > > > > Hmm.. I'm seeing a failure with found being -1, which means ... > > > > > +} > > > + > > > +void test_kmem_cache_iter(void) > > > +{ > > > + DECLARE_LIBBPF_OPTS(bpf_iter_attach_opts, opts); > > > + struct kmem_cache_iter *skel = NULL; > > > + union bpf_iter_link_info linfo = {}; > > > + struct bpf_link *link; > > > + char buf[1024]; > > > + int iter_fd; > > > + > > > + skel = kmem_cache_iter__open_and_load(); > > > + if (!ASSERT_OK_PTR(skel, "kmem_cache_iter__open_and_load")) > > > + return; > > > + > > > + opts.link_info = &linfo; > > > + opts.link_info_len = sizeof(linfo); > > > + > > > + link = bpf_program__attach_iter(skel->progs.slab_info_collector, &opts); > > > + if (!ASSERT_OK_PTR(link, "attach_iter")) > > > + goto destroy; > > > + > > > + iter_fd = bpf_iter_create(bpf_link__fd(link)); > > > + if (!ASSERT_GE(iter_fd, 0, "iter_create")) > > > + goto free_link; > > > + > > > + memset(buf, 0, sizeof(buf)); > > > + while (read(iter_fd, buf, sizeof(buf) > 0)) { > > > + /* read out all contents */ > > > + printf("%s", buf); > > > + } > > > + > > > + /* next reads should return 0 */ > > > + ASSERT_EQ(read(iter_fd, buf, sizeof(buf)), 0, "read"); > > > + > > > + test_kmem_cache_iter_check_task(skel); > > > + > > > + close(iter_fd); > > > + > > > +free_link: > > > + bpf_link__destroy(link); > > > +destroy: > > > + kmem_cache_iter__destroy(skel); > > > +} > > > diff --git a/tools/testing/selftests/bpf/progs/bpf_iter.h b/tools/testing/selftests/bpf/progs/bpf_iter.h > > > index c41ee80533ca219a..3305dc3a74b32481 100644 > > > --- a/tools/testing/selftests/bpf/progs/bpf_iter.h > > > +++ b/tools/testing/selftests/bpf/progs/bpf_iter.h > > > @@ -24,6 +24,7 @@ > > > #define BTF_F_PTR_RAW BTF_F_PTR_RAW___not_used > > > #define BTF_F_ZERO BTF_F_ZERO___not_used > > > #define bpf_iter__ksym bpf_iter__ksym___not_used > > > +#define bpf_iter__kmem_cache bpf_iter__kmem_cache___not_used > > > #include "vmlinux.h" > > > #undef bpf_iter_meta > > > #undef bpf_iter__bpf_map > > > @@ -48,6 +49,7 @@ > > > #undef BTF_F_PTR_RAW > > > #undef BTF_F_ZERO > > > #undef bpf_iter__ksym > > > +#undef bpf_iter__kmem_cache > > > > > > struct bpf_iter_meta { > > > struct seq_file *seq; > > > @@ -165,3 +167,8 @@ struct bpf_iter__ksym { > > > struct bpf_iter_meta *meta; > > > struct kallsym_iter *ksym; > > > }; > > > + > > > +struct bpf_iter__kmem_cache { > > > + struct bpf_iter_meta *meta; > > > + struct kmem_cache *s; > > > +} __attribute__((preserve_access_index)); > > > diff --git a/tools/testing/selftests/bpf/progs/kmem_cache_iter.c b/tools/testing/selftests/bpf/progs/kmem_cache_iter.c > > > new file mode 100644 > > > index 0000000000000000..3f6ec15a1bf6344c > > > --- /dev/null > > > +++ b/tools/testing/selftests/bpf/progs/kmem_cache_iter.c > > > @@ -0,0 +1,66 @@ > > > +// SPDX-License-Identifier: GPL-2.0 > > > +/* Copyright (c) 2024 Google */ > > > + > > > +#include "bpf_iter.h" > > > +#include > > > +#include > > > + > > > +char _license[] SEC("license") = "GPL"; > > > + > > > +#define SLAB_NAME_MAX 256 > > > + > > > +struct { > > > + __uint(type, BPF_MAP_TYPE_HASH); > > > + __uint(key_size, sizeof(void *)); > > > + __uint(value_size, SLAB_NAME_MAX); > > > + __uint(max_entries, 1024); > > > +} slab_hash SEC(".maps"); > > > + > > > +extern struct kmem_cache *bpf_get_kmem_cache(__u64 addr) __ksym; > > > + > > > +/* result, will be checked by userspace */ > > > +int found; > > > + > > > +SEC("iter/kmem_cache") > > > +int slab_info_collector(struct bpf_iter__kmem_cache *ctx) > > > +{ > > > + struct seq_file *seq = ctx->meta->seq; > > > + struct kmem_cache *s = ctx->s; > > > + > > > + if (s) { > > > + char name[SLAB_NAME_MAX]; > > > + > > > + /* > > > + * To make sure if the slab_iter implements the seq interface > > > + * properly and it's also useful for debugging. > > > + */ > > > + BPF_SEQ_PRINTF(seq, "%s: %u\n", s->name, s->object_size); > > > + > > > + bpf_probe_read_kernel_str(name, sizeof(name), s->name); > > > + bpf_map_update_elem(&slab_hash, &s, name, BPF_NOEXIST); > > > + } > > > + > > > + return 0; > > > +} > > > + > > > +SEC("raw_tp/bpf_test_finish") > > > +int BPF_PROG(check_task_struct) > > > +{ > > > + __u64 curr = bpf_get_current_task(); > > > + struct kmem_cache *s; > > > + char *name; > > > + > > > + s = bpf_get_kmem_cache(curr); > > > + if (s == NULL) { > > > + found = -1; > > > + return 0; > > > > ... it cannot find a kmem_cache for the current task. This program is > > run by bpf_prog_test_run_opts() with BPF_F_TEST_RUN_ON_CPU. So I think > > the curr should point a task_struct in a slab cache. > > > > Am I missing something? > > Hi Namhyung, > > Out of curiosity I've been investigating this issue on my machine and > running some experiments. Thanks a lot for looking at this! > > When the test fails, calling dump_page() for the page the task_struct > belongs to, > shows that the page does not have the PGTY_slab flag set which is why > virt_to_slab(current) returns NULL. > > Does the test always fails on your environment? On my machine, the > test passed sometimes but failed some times. I'm using vmtest.sh but it succeeded mostly. I thought I couldn't reproduce it locally, but I also see the failure sometimes. I'll take a deeper look. > > Maybe sometimes the value returned by 'current' macro belongs to a > slab, but sometimes it does not. > But that doesn't really make sense to me as IIUC task_struct > descriptors are allocated from slab. AFAIK the notable exception is the init_task which lives in the kernel data. I'm not sure the if the test is running by PID 1. > > ....Or maybe some code can overwrote the page_type field of a slab? > Hmm, it seems we need more information to identify what's gone wrong. I doubt it's the case, but who knows? :) > > Just FYI, adding the output of the following code snippet in > bpf_get_kmem_cache(): > > pr_info("current = %llx\n", (unsigned long long)current); > dump_page(virt_to_head_page(current), "virt_to_head_page()"); Thanks, I'll try this in my test too. Namhyung > > # When the test passes > [ 232.755028] current = ffff8ff5b9ebd200 > [ 232.755031] page: refcount:1 mapcount:0 mapping:0000000000000000 > index:0x0 pfn:0x139eb8 > [ 232.755033] head: order:3 mapcount:0 entire_mapcount:0 > nr_pages_mapped:0 pincount:0 > [ 232.755035] memcg:ffff8ff5b3ee0c01 > [ 232.755037] ksm flags: > 0x17ffffc0000040(head|node=0|zone=2|lastcpupid=0x1fffff) > [ 232.755040] page_type: f5(slab) > [ 232.755042] raw: 0017ffffc0000040 ffff8ff58028ab00 ffffdaba05b8fc00 > dead000000000003 > [ 232.755045] raw: 0000000000000000 0000000000030003 00000001f5000000 > ffff8ff5b3ee0c01 > [ 232.755047] head: 0017ffffc0000040 ffff8ff58028ab00 > ffffdaba05b8fc00 dead000000000003 > [ 232.755048] head: 0000000000000000 0000000000030003 > 00000001f5000000 ffff8ff5b3ee0c01 > [ 232.755050] head: 0017ffffc0000003 ffffdaba04e7ae01 > ffffffffffffffff 0000000000000000 > [ 232.755052] head: 0000000000000008 0000000000000000 > 00000000ffffffff 0000000000000000 > [ 232.755053] page dumped because: virt_to_head_page() > > # When the test fails > [ 130.811626] current = ffffffff884110c0 > [ 130.811628] page: refcount:1 mapcount:0 mapping:0000000000000000 > index:0x0 pfn:0x8a9411 > [ 130.811632] flags: > 0x17ffffc0002000(reserved|node=0|zone=2|lastcpupid=0x1fffff) > [ 130.811636] raw: 0017ffffc0002000 ffffdaba22a50448 ffffdaba22a50448 > 0000000000000000 > [ 130.811639] raw: 0000000000000000 0000000000000000 00000001ffffffff > 0000000000000000 > [ 130.811641] page dumped because: virt_to_head_page() > > Best, > Hyeonggon > > > > > Thanks, > > Namhyung > > > > > + } > > > + > > > + name = bpf_map_lookup_elem(&slab_hash, &s); > > > + if (name && !bpf_strncmp(name, 11, "task_struct")) > > > + found = 1; > > > + else > > > + found = -2; > > > + > > > + return 0; > > > +} > > > -- > > > 2.46.1.824.gd892dcdcdd-goog > > >