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Message-ID: <f780fc3a-dbc2-986c-d5a0-6b0ef1c4311f@fb.com>
Date: Wed, 2 Mar 2022 18:03:16 -0800
From: Yonghong Song <yhs@...com>
To: Kumar Kartikeya Dwivedi <memxor@...il.com>,
Hao Luo <haoluo@...gle.com>
Cc: Alexei Starovoitov <ast@...nel.org>,
Andrii Nakryiko <andrii@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Martin KaFai Lau <kafai@...com>,
Song Liu <songliubraving@...com>,
KP Singh <kpsingh@...nel.org>,
Shakeel Butt <shakeelb@...gle.com>,
Joe Burton <jevburton.kernel@...il.com>,
Tejun Heo <tj@...nel.org>, joshdon@...gle.com, sdf@...gle.com,
bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v1 8/9] bpf: Introduce cgroup iter
On 3/2/22 2:45 PM, Kumar Kartikeya Dwivedi wrote:
> On Sat, Feb 26, 2022 at 05:13:38AM IST, Hao Luo wrote:
>> Introduce a new type of iter prog: cgroup. Unlike other bpf_iter, this
>> iter doesn't iterate a set of kernel objects. Instead, it is supposed to
>> be parameterized by a cgroup id and prints only that cgroup. So one
>> needs to specify a target cgroup id when attaching this iter.
>>
>> The target cgroup's state can be read out via a link of this iter.
>> Typically, we can monitor cgroup creation and deletion using sleepable
>> tracing and use it to create corresponding directories in bpffs and pin
>> a cgroup id parameterized link in the directory. Then we can read the
>> auto-pinned iter link to get cgroup's state. The output of the iter link
>> is determined by the program. See the selftest test_cgroup_stats.c for
>> an example.
>>
>> Signed-off-by: Hao Luo <haoluo@...gle.com>
>> ---
>> include/linux/bpf.h | 1 +
>> include/uapi/linux/bpf.h | 6 ++
>> kernel/bpf/Makefile | 2 +-
>> kernel/bpf/cgroup_iter.c | 141 +++++++++++++++++++++++++++++++++
>> tools/include/uapi/linux/bpf.h | 6 ++
>> 5 files changed, 155 insertions(+), 1 deletion(-)
>> create mode 100644 kernel/bpf/cgroup_iter.c
>>
>> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
>> index 759ade7b24b3..3ce9b0b7ed89 100644
>> --- a/include/linux/bpf.h
>> +++ b/include/linux/bpf.h
>> @@ -1595,6 +1595,7 @@ int bpf_obj_get_path(bpfptr_t pathname, int flags);
>>
>> struct bpf_iter_aux_info {
>> struct bpf_map *map;
>> + u64 cgroup_id;
>> };
>>
>> typedef int (*bpf_iter_attach_target_t)(struct bpf_prog *prog,
>> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
>> index a5dbc794403d..855ad80d9983 100644
>> --- a/include/uapi/linux/bpf.h
>> +++ b/include/uapi/linux/bpf.h
>> @@ -91,6 +91,9 @@ union bpf_iter_link_info {
>> struct {
>> __u32 map_fd;
>> } map;
>> + struct {
>> + __u64 cgroup_id;
>> + } cgroup;
>> };
>>
>> /* BPF syscall commands, see bpf(2) man-page for more details. */
>> @@ -5887,6 +5890,9 @@ struct bpf_link_info {
>> struct {
>> __u32 map_id;
>> } map;
>> + struct {
>> + __u64 cgroup_id;
>> + } cgroup;
>> };
>> } iter;
>> struct {
>> diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
>> index c1a9be6a4b9f..52a0e4c6e96e 100644
>> --- a/kernel/bpf/Makefile
>> +++ b/kernel/bpf/Makefile
>> @@ -8,7 +8,7 @@ CFLAGS_core.o += $(call cc-disable-warning, override-init) $(cflags-nogcse-yy)
>>
>> obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o tnum.o bpf_iter.o map_iter.o task_iter.o prog_iter.o
>> obj-$(CONFIG_BPF_SYSCALL) += hashtab.o arraymap.o percpu_freelist.o bpf_lru_list.o lpm_trie.o map_in_map.o bloom_filter.o
>> -obj-$(CONFIG_BPF_SYSCALL) += local_storage.o queue_stack_maps.o ringbuf.o
>> +obj-$(CONFIG_BPF_SYSCALL) += local_storage.o queue_stack_maps.o ringbuf.o cgroup_iter.o
>> obj-$(CONFIG_BPF_SYSCALL) += bpf_local_storage.o bpf_task_storage.o
>> obj-${CONFIG_BPF_LSM} += bpf_inode_storage.o
>> obj-$(CONFIG_BPF_SYSCALL) += disasm.o
>> diff --git a/kernel/bpf/cgroup_iter.c b/kernel/bpf/cgroup_iter.c
>> new file mode 100644
>> index 000000000000..011d9dcd1d51
>> --- /dev/null
>> +++ b/kernel/bpf/cgroup_iter.c
>> @@ -0,0 +1,141 @@
>> +// SPDX-License-Identifier: GPL-2.0-only
>> +/* Copyright (c) 2022 Google */
>> +#include <linux/bpf.h>
>> +#include <linux/btf_ids.h>
>> +#include <linux/cgroup.h>
>> +#include <linux/kernel.h>
>> +#include <linux/seq_file.h>
>> +
>> +struct bpf_iter__cgroup {
>> + __bpf_md_ptr(struct bpf_iter_meta *, meta);
>> + __bpf_md_ptr(struct cgroup *, cgroup);
>> +};
>> +
>> +static void *cgroup_iter_seq_start(struct seq_file *seq, loff_t *pos)
>> +{
>> + struct cgroup *cgroup;
>> + u64 cgroup_id;
>> +
>> + /* Only one session is supported. */
>> + if (*pos > 0)
>> + return NULL;
>> +
>> + cgroup_id = *(u64 *)seq->private;
>> + cgroup = cgroup_get_from_id(cgroup_id);
>> + if (!cgroup)
>> + return NULL;
>> +
>> + if (*pos == 0)
>> + ++*pos;
>> +
>> + return cgroup;
>> +}
>> +
>> +static void *cgroup_iter_seq_next(struct seq_file *seq, void *v, loff_t *pos)
>> +{
>> + ++*pos;
>> + return NULL;
>> +}
>> +
>> +static int cgroup_iter_seq_show(struct seq_file *seq, void *v)
>> +{
>> + struct bpf_iter__cgroup ctx;
>> + struct bpf_iter_meta meta;
>> + struct bpf_prog *prog;
>> + int ret = 0;
>> +
>> + ctx.meta = &meta;
>> + ctx.cgroup = v;
>> + meta.seq = seq;
>> + prog = bpf_iter_get_info(&meta, false);
>> + if (prog)
>> + ret = bpf_iter_run_prog(prog, &ctx);
>> +
>> + return ret;
>> +}
>> +
>> +static void cgroup_iter_seq_stop(struct seq_file *seq, void *v)
>> +{
>> + if (v)
>> + cgroup_put(v);
>> +}
>
> I think in existing iterators, we make a final call to seq_show, with v as NULL,
> is there a specific reason to do it differently for this? There is logic in
> bpf_iter.c to trigger ->stop() callback again when ->start() or ->next() returns
> NULL, to execute BPF program with NULL p, see the comment above stop label.
>
> If you do add the seq_show call with NULL, you'd also need to change the
> ctx_arg_info PTR_TO_BTF_ID to PTR_TO_BTF_ID_OR_NULL.
Kumar, PTR_TO_BTF_ID should be okay since the show() never takes a
non-NULL cgroup. But we do have issues for cgroup_iter_seq_stop() which
I missed earlier.
For cgroup_iter, the following is the current workflow:
start -> not NULL -> show -> next -> NULL -> stop
or
start -> NULL -> stop
So for cgroup_iter_seq_stop, the input parameter 'v' will be NULL, so
the cgroup_put() is not actually called, i.e., corresponding cgroup is
not freed.
There are two ways to fix the issue:
. call cgroup_put() in next() before return NULL. This way,
stop() will be a noop.
. put cgroup_get_from_id() and cgroup_put() in
bpf_iter_attach_cgroup() and bpf_iter_detach_cgroup().
I prefer the second approach as it is cleaner.
>
>> +
>> +static const struct seq_operations cgroup_iter_seq_ops = {
>> + .start = cgroup_iter_seq_start,
>> + .next = cgroup_iter_seq_next,
>> + .stop = cgroup_iter_seq_stop,
>> + .show = cgroup_iter_seq_show,
>> +};
>> +
>> +BTF_ID_LIST_SINGLE(bpf_cgroup_btf_id, struct, cgroup)
>> +
>> +static int cgroup_iter_seq_init(void *priv_data, struct bpf_iter_aux_info *aux)
>> +{
>> + *(u64 *)priv_data = aux->cgroup_id;
>> + return 0;
>> +}
>> +
>> +static void cgroup_iter_seq_fini(void *priv_data)
>> +{
>> +}
>> +
>> +static const struct bpf_iter_seq_info cgroup_iter_seq_info = {
>> + .seq_ops = &cgroup_iter_seq_ops,
>> + .init_seq_private = cgroup_iter_seq_init,
>> + .fini_seq_private = cgroup_iter_seq_fini,
>> + .seq_priv_size = sizeof(u64),
>> +};
>> +
>> +static int bpf_iter_attach_cgroup(struct bpf_prog *prog,
>> + union bpf_iter_link_info *linfo,
>> + struct bpf_iter_aux_info *aux)
>> +{
>> + aux->cgroup_id = linfo->cgroup.cgroup_id;
>> + return 0;
>> +}
>> +
>> +static void bpf_iter_detach_cgroup(struct bpf_iter_aux_info *aux)
>> +{
>> +}
>> +
>> +void bpf_iter_cgroup_show_fdinfo(const struct bpf_iter_aux_info *aux,
>> + struct seq_file *seq)
>> +{
>> + char buf[64] = {0};
>> +
>> + cgroup_path_from_kernfs_id(aux->cgroup_id, buf, sizeof(buf));
>> + seq_printf(seq, "cgroup_id:\t%lu\n", aux->cgroup_id);
>> + seq_printf(seq, "cgroup_path:\t%s\n", buf);
>> +}
>> +
>> +int bpf_iter_cgroup_fill_link_info(const struct bpf_iter_aux_info *aux,
>> + struct bpf_link_info *info)
>> +{
>> + info->iter.cgroup.cgroup_id = aux->cgroup_id;
>> + return 0;
>> +}
>> +
>> +DEFINE_BPF_ITER_FUNC(cgroup, struct bpf_iter_meta *meta,
>> + struct cgroup *cgroup)
>> +
>> +static struct bpf_iter_reg bpf_cgroup_reg_info = {
>> + .target = "cgroup",
>> + .attach_target = bpf_iter_attach_cgroup,
>> + .detach_target = bpf_iter_detach_cgroup,
>> + .show_fdinfo = bpf_iter_cgroup_show_fdinfo,
>> + .fill_link_info = bpf_iter_cgroup_fill_link_info,
>> + .ctx_arg_info_size = 1,
>> + .ctx_arg_info = {
>> + { offsetof(struct bpf_iter__cgroup, cgroup),
>> + PTR_TO_BTF_ID },
>> + },
>> + .seq_info = &cgroup_iter_seq_info,
>> +};
>> +
>> +static int __init bpf_cgroup_iter_init(void)
>> +{
>> + bpf_cgroup_reg_info.ctx_arg_info[0].btf_id = bpf_cgroup_btf_id[0];
>> + return bpf_iter_reg_target(&bpf_cgroup_reg_info);
>> +}
>> +
>> +late_initcall(bpf_cgroup_iter_init);
>> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
>> index a5dbc794403d..855ad80d9983 100644
>> --- a/tools/include/uapi/linux/bpf.h
>> +++ b/tools/include/uapi/linux/bpf.h
>> @@ -91,6 +91,9 @@ union bpf_iter_link_info {
>> struct {
>> __u32 map_fd;
>> } map;
>> + struct {
>> + __u64 cgroup_id;
>> + } cgroup;
>> };
>>
>> /* BPF syscall commands, see bpf(2) man-page for more details. */
>> @@ -5887,6 +5890,9 @@ struct bpf_link_info {
>> struct {
>> __u32 map_id;
>> } map;
>> + struct {
>> + __u64 cgroup_id;
>> + } cgroup;
>> };
>> } iter;
>> struct {
>> --
>> 2.35.1.574.g5d30c73bfb-goog
>>
>
> --
> Kartikeya
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