Messages in this thread | | | Date | Mon, 27 Jun 2022 21:09:35 -0700 | Subject | Re: [PATCH bpf-next v2 4/8] bpf: Introduce cgroup iter | From | Yonghong Song <> |
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On 6/10/22 12:44 PM, Yosry Ahmed wrote: > From: Hao Luo <haoluo@google.com> > > Cgroup_iter is a type of bpf_iter. It walks over cgroups in two modes: > > - walking a cgroup's descendants. > - walking a cgroup's ancestors.
The implementation has another choice, BPF_ITER_CGROUP_PARENT_UP. We should add it here as well.
> > When attaching cgroup_iter, one can set a cgroup to the iter_link > created from attaching. This cgroup is passed as a file descriptor and > serves as the starting point of the walk. If no cgroup is specified, > the starting point will be the root cgroup. > > For walking descendants, one can specify the order: either pre-order or > post-order. For walking ancestors, the walk starts at the specified > cgroup and ends at the root. > > One can also terminate the walk early by returning 1 from the iter > program. > > Note that because walking cgroup hierarchy holds cgroup_mutex, the iter > program is called with cgroup_mutex held.
Overall looks good to me with a few nits below.
Acked-by: Yonghong Song <yhs@fb.com>
> > Signed-off-by: Hao Luo <haoluo@google.com> > Signed-off-by: Yosry Ahmed <yosryahmed@google.com> > --- > include/linux/bpf.h | 8 ++ > include/uapi/linux/bpf.h | 21 +++ > kernel/bpf/Makefile | 2 +- > kernel/bpf/cgroup_iter.c | 235 +++++++++++++++++++++++++++++++++ > tools/include/uapi/linux/bpf.h | 21 +++ > 5 files changed, 286 insertions(+), 1 deletion(-) > create mode 100644 kernel/bpf/cgroup_iter.c > > diff --git a/include/linux/bpf.h b/include/linux/bpf.h > index 8e6092d0ea956..48d8e836b9748 100644 > --- a/include/linux/bpf.h > +++ b/include/linux/bpf.h > @@ -44,6 +44,7 @@ struct kobject; > struct mem_cgroup; > struct module; > struct bpf_func_state; > +struct cgroup; > > extern struct idr btf_idr; > extern spinlock_t btf_idr_lock; > @@ -1590,7 +1591,14 @@ int bpf_obj_get_user(const char __user *pathname, int flags); > int __init bpf_iter_ ## target(args) { return 0; } > > struct bpf_iter_aux_info { > + /* for map_elem iter */ > struct bpf_map *map; > + > + /* for cgroup iter */ > + struct { > + struct cgroup *start; /* starting cgroup */ > + int order; > + } cgroup; > }; > > 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 f4009dbdf62da..4fd05cde19116 100644 > --- a/include/uapi/linux/bpf.h > +++ b/include/uapi/linux/bpf.h > @@ -87,10 +87,27 @@ struct bpf_cgroup_storage_key { > __u32 attach_type; /* program attach type (enum bpf_attach_type) */ > }; > > +enum bpf_iter_cgroup_traversal_order { > + BPF_ITER_CGROUP_PRE = 0, /* pre-order traversal */ > + BPF_ITER_CGROUP_POST, /* post-order traversal */ > + BPF_ITER_CGROUP_PARENT_UP, /* traversal of ancestors up to the root */ > +}; > + > union bpf_iter_link_info { > struct { > __u32 map_fd; > } map; > + > + /* cgroup_iter walks either the live descendants of a cgroup subtree, or the ancestors > + * of a given cgroup. > + */ > + struct { > + /* Cgroup file descriptor. This is root of the subtree if for walking the > + * descendants; this is the starting cgroup if for walking the ancestors. > + */ > + __u32 cgroup_fd; > + __u32 traversal_order; > + } cgroup; > }; > > /* BPF syscall commands, see bpf(2) man-page for more details. */ > @@ -6050,6 +6067,10 @@ struct bpf_link_info { > struct { > __u32 map_id; > } map; > + struct { > + __u32 traversal_order; > + __aligned_u64 cgroup_id; > + } cgroup; > }; > } iter; > struct { > diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile > index 057ba8e01e70f..9741b9314fb46 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 link_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 0000000000000..88deb655efa71 > --- /dev/null > +++ b/kernel/bpf/cgroup_iter.c > @@ -0,0 +1,235 @@ > +// 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> > + > +#include "../cgroup/cgroup-internal.h" /* cgroup_mutex and cgroup_is_dead */ > + > +/* cgroup_iter provides two modes of traversal to the cgroup hierarchy. > + * > + * 1. Walk the descendants of a cgroup. > + * 2. Walk the ancestors of a cgroup.
three modes here?
> + * > + * For walking descendants, cgroup_iter can walk in either pre-order or > + * post-order. For walking ancestors, the iter walks up from a cgroup to > + * the root. > + * > + * The iter program can terminate the walk early by returning 1. Walk > + * continues if prog returns 0. > + * > + * The prog can check (seq->num == 0) to determine whether this is > + * the first element. The prog may also be passed a NULL cgroup, > + * which means the walk has completed and the prog has a chance to > + * do post-processing, such as outputing an epilogue. > + * > + * Note: the iter_prog is called with cgroup_mutex held. > + */ > + > +struct bpf_iter__cgroup { > + __bpf_md_ptr(struct bpf_iter_meta *, meta); > + __bpf_md_ptr(struct cgroup *, cgroup); > +}; > + > +struct cgroup_iter_priv { > + struct cgroup_subsys_state *start_css; > + bool terminate; > + int order; > +}; > + > +static void *cgroup_iter_seq_start(struct seq_file *seq, loff_t *pos) > +{ > + struct cgroup_iter_priv *p = seq->private; > + > + mutex_lock(&cgroup_mutex); > + > + /* support only one session */ > + if (*pos > 0) > + return NULL; > + > + ++*pos; > + p->terminate = false; > + if (p->order == BPF_ITER_CGROUP_PRE) > + return css_next_descendant_pre(NULL, p->start_css); > + else if (p->order == BPF_ITER_CGROUP_POST) > + return css_next_descendant_post(NULL, p->start_css); > + else /* BPF_ITER_CGROUP_PARENT_UP */ > + return p->start_css; > +} > + > +static int __cgroup_iter_seq_show(struct seq_file *seq, > + struct cgroup_subsys_state *css, int in_stop); > + > +static void cgroup_iter_seq_stop(struct seq_file *seq, void *v) > +{ > + /* pass NULL to the prog for post-processing */ > + if (!v) > + __cgroup_iter_seq_show(seq, NULL, true); > + mutex_unlock(&cgroup_mutex); > +} > + > +static void *cgroup_iter_seq_next(struct seq_file *seq, void *v, loff_t *pos) > +{ > + struct cgroup_subsys_state *curr = (struct cgroup_subsys_state *)v; > + struct cgroup_iter_priv *p = seq->private; > + > + ++*pos; > + if (p->terminate) > + return NULL; > + > + if (p->order == BPF_ITER_CGROUP_PRE) > + return css_next_descendant_pre(curr, p->start_css); > + else if (p->order == BPF_ITER_CGROUP_POST) > + return css_next_descendant_post(curr, p->start_css); > + else > + return curr->parent; > +} > + > +static int __cgroup_iter_seq_show(struct seq_file *seq, > + struct cgroup_subsys_state *css, int in_stop) > +{ > + struct cgroup_iter_priv *p = seq->private; > + struct bpf_iter__cgroup ctx; > + struct bpf_iter_meta meta; > + struct bpf_prog *prog; > + int ret = 0; > + > + /* cgroup is dead, skip this element */ > + if (css && cgroup_is_dead(css->cgroup)) > + return 0; > + > + ctx.meta = &meta; > + ctx.cgroup = css ? css->cgroup : NULL; > + meta.seq = seq; > + prog = bpf_iter_get_info(&meta, in_stop); > + if (prog) > + ret = bpf_iter_run_prog(prog, &ctx); > + > + /* if prog returns > 0, terminate after this element. */ > + if (ret != 0) > + p->terminate = true; > + > + return 0; > +} > + > +static int cgroup_iter_seq_show(struct seq_file *seq, void *v) > +{ > + return __cgroup_iter_seq_show(seq, (struct cgroup_subsys_state *)v, > + false); > +} > + > +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, struct bpf_iter_aux_info *aux) > +{ > + struct cgroup_iter_priv *p = (struct cgroup_iter_priv *)priv; > + struct cgroup *cgrp = aux->cgroup.start; > + > + p->start_css = &cgrp->self; > + p->terminate = false; > + p->order = aux->cgroup.order; > + return 0; > +} > + > +static const struct bpf_iter_seq_info cgroup_iter_seq_info = { > + .seq_ops = &cgroup_iter_seq_ops, > + .init_seq_private = cgroup_iter_seq_init, > + .seq_priv_size = sizeof(struct cgroup_iter_priv), > +}; > + > +static int bpf_iter_attach_cgroup(struct bpf_prog *prog, > + union bpf_iter_link_info *linfo, > + struct bpf_iter_aux_info *aux) > +{ > + int fd = linfo->cgroup.cgroup_fd; > + struct cgroup *cgrp; > + > + if (fd) > + cgrp = cgroup_get_from_fd(fd); > + else /* walk the entire hierarchy by default. */ > + cgrp = cgroup_get_from_path("/"); > + > + if (IS_ERR(cgrp)) > + return PTR_ERR(cgrp); > + > + aux->cgroup.start = cgrp; > + aux->cgroup.order = linfo->cgroup.traversal_order;
The legality of traversal_order should be checked.
> + return 0; > +} > + > +static void bpf_iter_detach_cgroup(struct bpf_iter_aux_info *aux) > +{ > + cgroup_put(aux->cgroup.start); > +} > + > +static void bpf_iter_cgroup_show_fdinfo(const struct bpf_iter_aux_info *aux, > + struct seq_file *seq) > +{ > + char *buf; > + > + buf = kzalloc(PATH_MAX, GFP_KERNEL); > + if (!buf) { > + seq_puts(seq, "cgroup_path:\n");
This is a really unlikely case. maybe "cgroup_path:<unknown>"?
> + goto show_order; > + } > + > + /* If cgroup_path_ns() fails, buf will be an empty string, cgroup_path > + * will print nothing. > + * > + * Path is in the calling process's cgroup namespace. > + */ > + cgroup_path_ns(aux->cgroup.start, buf, PATH_MAX, > + current->nsproxy->cgroup_ns); > + seq_printf(seq, "cgroup_path:\t%s\n", buf); > + kfree(buf); > + > +show_order: > + if (aux->cgroup.order == BPF_ITER_CGROUP_PRE) > + seq_puts(seq, "traversal_order: pre\n"); > + else if (aux->cgroup.order == BPF_ITER_CGROUP_POST) > + seq_puts(seq, "traversal_order: post\n"); > + else /* BPF_ITER_CGROUP_PARENT_UP */ > + seq_puts(seq, "traversal_order: parent_up\n"); > +} > + [...]
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