Messages in this thread | | | Date | Wed, 2 Mar 2022 18:03:16 -0800 | Subject | Re: [PATCH bpf-next v1 8/9] bpf: Introduce cgroup iter | From | Yonghong Song <> |
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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@google.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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