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[34.90.50.93]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-b8dbefc667asm116547566b.22.2026.01.28.03.25.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 28 Jan 2026 03:25:35 -0800 (PST) Date: Wed, 28 Jan 2026 11:25:31 +0000 From: Matt Bobrowski To: Roman Gushchin Cc: bpf@vger.kernel.org, Michal Hocko , Alexei Starovoitov , Shakeel Butt , JP Kobryn , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Suren Baghdasaryan , Johannes Weiner , Andrew Morton Subject: Re: [PATCH bpf-next v3 02/17] bpf: allow attaching struct_ops to cgroups Message-ID: References: <20260127024421.494929-1-roman.gushchin@linux.dev> <20260127024421.494929-3-roman.gushchin@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260127024421.494929-3-roman.gushchin@linux.dev> On Mon, Jan 26, 2026 at 06:44:05PM -0800, Roman Gushchin wrote: > Introduce an ability to attach bpf struct_ops'es to cgroups. > > From user's standpoint it works in the following way: > a user passes a BPF_F_CGROUP_FD flag and specifies the target cgroup > fd while creating a struct_ops link. As the result, the bpf struct_ops > link will be created and attached to a cgroup. > > The cgroup.bpf structure maintains a list of attached struct ops links. > If the cgroup is getting deleted, attached struct ops'es are getting > auto-detached and the userspace program gets a notification. > > This change doesn't answer the question how bpf programs belonging > to these struct ops'es will be executed. It will be done individually > for every bpf struct ops which supports this. > > Please, note that unlike "normal" bpf programs, struct ops'es > are not propagated to cgroup sub-trees. > > Signed-off-by: Roman Gushchin > --- > include/linux/bpf-cgroup-defs.h | 3 ++ > include/linux/bpf-cgroup.h | 16 +++++++++ > include/linux/bpf.h | 3 ++ > include/uapi/linux/bpf.h | 3 ++ > kernel/bpf/bpf_struct_ops.c | 59 ++++++++++++++++++++++++++++++--- > kernel/bpf/cgroup.c | 46 +++++++++++++++++++++++++ > tools/include/uapi/linux/bpf.h | 1 + > 7 files changed, 127 insertions(+), 4 deletions(-) > > diff --git a/include/linux/bpf-cgroup-defs.h b/include/linux/bpf-cgroup-defs.h > index c9e6b26abab6..6c5e37190dad 100644 > --- a/include/linux/bpf-cgroup-defs.h > +++ b/include/linux/bpf-cgroup-defs.h > @@ -71,6 +71,9 @@ struct cgroup_bpf { > /* temp storage for effective prog array used by prog_attach/detach */ > struct bpf_prog_array *inactive; > > + /* list of bpf struct ops links */ > + struct list_head struct_ops_links; > + > /* reference counter used to detach bpf programs after cgroup removal */ > struct percpu_ref refcnt; > > diff --git a/include/linux/bpf-cgroup.h b/include/linux/bpf-cgroup.h > index 2f535331f926..a6c327257006 100644 > --- a/include/linux/bpf-cgroup.h > +++ b/include/linux/bpf-cgroup.h > @@ -423,6 +423,11 @@ int cgroup_bpf_link_attach(const union bpf_attr *attr, struct bpf_prog *prog); > int cgroup_bpf_prog_query(const union bpf_attr *attr, > union bpf_attr __user *uattr); > > +int cgroup_bpf_attach_struct_ops(struct cgroup *cgrp, > + struct bpf_struct_ops_link *link); > +void cgroup_bpf_detach_struct_ops(struct cgroup *cgrp, > + struct bpf_struct_ops_link *link); > + > const struct bpf_func_proto * > cgroup_common_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog); > #else > @@ -451,6 +456,17 @@ static inline int cgroup_bpf_link_attach(const union bpf_attr *attr, > return -EINVAL; > } > > +static inline int cgroup_bpf_attach_struct_ops(struct cgroup *cgrp, > + struct bpf_struct_ops_link *link) > +{ > + return -EINVAL; > +} > + > +static inline void cgroup_bpf_detach_struct_ops(struct cgroup *cgrp, > + struct bpf_struct_ops_link *link) > +{ > +} > + > static inline int cgroup_bpf_prog_query(const union bpf_attr *attr, > union bpf_attr __user *uattr) > { > diff --git a/include/linux/bpf.h b/include/linux/bpf.h > index 899dd911dc82..391888eb257c 100644 > --- a/include/linux/bpf.h > +++ b/include/linux/bpf.h > @@ -1894,6 +1894,9 @@ struct bpf_raw_tp_link { > struct bpf_struct_ops_link { > struct bpf_link link; > struct bpf_map __rcu *map; > + struct cgroup *cgroup; > + bool cgroup_removed; > + struct list_head list; > wait_queue_head_t wait_hup; > }; > > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h > index 44e7dbc278e3..28544e8af1cd 100644 > --- a/include/uapi/linux/bpf.h > +++ b/include/uapi/linux/bpf.h > @@ -1237,6 +1237,7 @@ enum bpf_perf_event_type { > #define BPF_F_AFTER (1U << 4) > #define BPF_F_ID (1U << 5) > #define BPF_F_PREORDER (1U << 6) > +#define BPF_F_CGROUP_FD (1U << 7) > #define BPF_F_LINK BPF_F_LINK /* 1 << 13 */ > > /* If BPF_F_STRICT_ALIGNMENT is used in BPF_PROG_LOAD command, the > @@ -6775,6 +6776,8 @@ struct bpf_link_info { > } xdp; > struct { > __u32 map_id; > + __u32 :32; > + __u64 cgroup_id; > } struct_ops; > struct { > __u32 pf; > diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c > index de01cf3025b3..2e361e22cfa0 100644 > --- a/kernel/bpf/bpf_struct_ops.c > +++ b/kernel/bpf/bpf_struct_ops.c > @@ -13,6 +13,8 @@ > #include > #include > #include > +#include > +#include > > struct bpf_struct_ops_value { > struct bpf_struct_ops_common_value common; > @@ -1220,6 +1222,10 @@ static void bpf_struct_ops_map_link_dealloc(struct bpf_link *link) > st_map->st_ops_desc->st_ops->unreg(&st_map->kvalue.data, link); > bpf_map_put(&st_map->map); > } > + > + if (st_link->cgroup) > + cgroup_bpf_detach_struct_ops(st_link->cgroup, st_link); > + > kfree(st_link); > } > > @@ -1228,6 +1234,7 @@ static void bpf_struct_ops_map_link_show_fdinfo(const struct bpf_link *link, > { > struct bpf_struct_ops_link *st_link; > struct bpf_map *map; > + u64 cgrp_id = 0; Assigning 0 to cgrp_id would technically be incorrect, right? Like, cgroup_id() for !CONFIG_CGROUPS default to returning 1, and for CONFIG_CGROUPS the ID allocation is done via the idr_alloc_cyclic() API using a range between 1 and INT_MAX. Perhaps here it serves as a valid sentinel value? Is that the rationale? In general, shouldn't all the cgroup related logic within this source file be protected by a CONFIG_CGROUPS ifdef? For example, both cgroup_get_from_fd() and cgroup_put() lack stubs when building with !CONFIG_CGROUPS. > st_link = container_of(link, struct bpf_struct_ops_link, link); > rcu_read_lock(); > @@ -1235,6 +1242,14 @@ static void bpf_struct_ops_map_link_show_fdinfo(const struct bpf_link *link, > if (map) > seq_printf(seq, "map_id:\t%d\n", map->id); > rcu_read_unlock(); > + > + cgroup_lock(); > + if (st_link->cgroup) > + cgrp_id = cgroup_id(st_link->cgroup); > + cgroup_unlock(); > + > + if (cgrp_id) > + seq_printf(seq, "cgroup_id:\t%llu\n", cgrp_id); Probably could introduce a simple inline helper for the cgroup_lock()/cgroup_id()/cgroup_unlock() dance that's going on in here and bpf_struct_ops_map_link_fill_link_info() below. > } > > static int bpf_struct_ops_map_link_fill_link_info(const struct bpf_link *link, > @@ -1242,6 +1257,7 @@ static int bpf_struct_ops_map_link_fill_link_info(const struct bpf_link *link, > { > struct bpf_struct_ops_link *st_link; > struct bpf_map *map; > + u64 cgrp_id = 0; > > st_link = container_of(link, struct bpf_struct_ops_link, link); > rcu_read_lock(); > @@ -1249,6 +1265,13 @@ static int bpf_struct_ops_map_link_fill_link_info(const struct bpf_link *link, > if (map) > info->struct_ops.map_id = map->id; > rcu_read_unlock(); > + > + cgroup_lock(); > + if (st_link->cgroup) > + cgrp_id = cgroup_id(st_link->cgroup); > + cgroup_unlock(); > + > + info->struct_ops.cgroup_id = cgrp_id; As mentioned above a simple inline helper could simply yield the following here: ... info->struct_ops.cgroup_id = bpf_struct_ops_lin_cgroup_id(); ... > return 0; > } > > @@ -1327,6 +1350,9 @@ static int bpf_struct_ops_map_link_detach(struct bpf_link *link) > > mutex_unlock(&update_mutex); > > + if (st_link->cgroup) > + cgroup_bpf_detach_struct_ops(st_link->cgroup, st_link); > + > wake_up_interruptible_poll(&st_link->wait_hup, EPOLLHUP); > > return 0; > @@ -1339,6 +1365,9 @@ static __poll_t bpf_struct_ops_map_link_poll(struct file *file, > > poll_wait(file, &st_link->wait_hup, pts); > > + if (st_link->cgroup_removed) > + return EPOLLHUP; > + > return rcu_access_pointer(st_link->map) ? 0 : EPOLLHUP; > } > > @@ -1357,8 +1386,12 @@ int bpf_struct_ops_link_create(union bpf_attr *attr) > struct bpf_link_primer link_primer; > struct bpf_struct_ops_map *st_map; > struct bpf_map *map; > + struct cgroup *cgrp; > int err; > > + if (attr->link_create.flags & ~BPF_F_CGROUP_FD) > + return -EINVAL; > + BPF_F_CGROUP_FD is dependent on the cgroup subsystem, therefore it probably makes some sense to only accept BPF_F_CGROUP_FD when CONFIG_BPF_CGROUP is enabled, otherwise -EOPNOTSUPP? I'd also probably rewrite this such that we do: ... struct cgroup *cgrp = NULL; ... if (attr->link_create.flags & ~BPF_F_CGROUP_FD) { #if IS_ENABLED(CONFIG_CGROUP_BPF) cgrp = cgroup_get_from_fd(attr->link_create.target_fd); if (IS_ERR(cgrp)) return PTR_ERR(cgrp); #else return -EOPNOTSUPP; #endif } ... if (cgrp) { link->cgroup = cgrp; if (cgroup_bpf_attach_struct_ops(cgrp, link)) { cgroup_put(cgrp); goto err_out; } } IMO the code is cleaner and reads better too. > map = bpf_map_get(attr->link_create.map_fd); > if (IS_ERR(map)) > return PTR_ERR(map); > @@ -1378,11 +1411,26 @@ int bpf_struct_ops_link_create(union bpf_attr *attr) > bpf_link_init(&link->link, BPF_LINK_TYPE_STRUCT_OPS, &bpf_struct_ops_map_lops, NULL, > attr->link_create.attach_type); > > + init_waitqueue_head(&link->wait_hup); > + > + if (attr->link_create.flags & BPF_F_CGROUP_FD) { > + cgrp = cgroup_get_from_fd(attr->link_create.target_fd); > + if (IS_ERR(cgrp)) { > + err = PTR_ERR(cgrp); > + goto err_out; > + } > + link->cgroup = cgrp; > + err = cgroup_bpf_attach_struct_ops(cgrp, link); > + if (err) { > + cgroup_put(cgrp); > + link->cgroup = NULL; > + goto err_out; > + } > + } > + > err = bpf_link_prime(&link->link, &link_primer); > if (err) > - goto err_out; > - > - init_waitqueue_head(&link->wait_hup); > + goto err_put_cgroup; > > /* Hold the update_mutex such that the subsystem cannot > * do link->ops->detach() before the link is fully initialized. > @@ -1393,13 +1441,16 @@ int bpf_struct_ops_link_create(union bpf_attr *attr) > mutex_unlock(&update_mutex); > bpf_link_cleanup(&link_primer); > link = NULL; > - goto err_out; > + goto err_put_cgroup; > } > RCU_INIT_POINTER(link->map, map); > mutex_unlock(&update_mutex); > > return bpf_link_settle(&link_primer); > > +err_put_cgroup: > + if (link && link->cgroup) > + cgroup_bpf_detach_struct_ops(link->cgroup, link); > err_out: > bpf_map_put(map); > kfree(link); > diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c > index 69988af44b37..7b1903be6f69 100644 > --- a/kernel/bpf/cgroup.c > +++ b/kernel/bpf/cgroup.c > @@ -16,6 +16,7 @@ > #include > #include > #include > +#include > #include > #include > > @@ -307,12 +308,23 @@ static void cgroup_bpf_release(struct work_struct *work) > bpf.release_work); > struct bpf_prog_array *old_array; > struct list_head *storages = &cgrp->bpf.storages; > + struct bpf_struct_ops_link *st_link, *st_tmp; > struct bpf_cgroup_storage *storage, *stmp; > + LIST_HEAD(st_links); > > unsigned int atype; > > cgroup_lock(); > > + list_splice_init(&cgrp->bpf.struct_ops_links, &st_links); > + list_for_each_entry_safe(st_link, st_tmp, &st_links, list) { > + st_link->cgroup = NULL; > + st_link->cgroup_removed = true; > + cgroup_put(cgrp); > + if (IS_ERR(bpf_link_inc_not_zero(&st_link->link))) > + list_del(&st_link->list); > + } > + > for (atype = 0; atype < ARRAY_SIZE(cgrp->bpf.progs); atype++) { > struct hlist_head *progs = &cgrp->bpf.progs[atype]; > struct bpf_prog_list *pl; > @@ -346,6 +358,11 @@ static void cgroup_bpf_release(struct work_struct *work) > > cgroup_unlock(); > > + list_for_each_entry_safe(st_link, st_tmp, &st_links, list) { > + st_link->link.ops->detach(&st_link->link); > + bpf_link_put(&st_link->link); > + } > + > for (p = cgroup_parent(cgrp); p; p = cgroup_parent(p)) > cgroup_bpf_put(p); > > @@ -525,6 +542,7 @@ static int cgroup_bpf_inherit(struct cgroup *cgrp) > INIT_HLIST_HEAD(&cgrp->bpf.progs[i]); > > INIT_LIST_HEAD(&cgrp->bpf.storages); > + INIT_LIST_HEAD(&cgrp->bpf.struct_ops_links); > > for (i = 0; i < NR; i++) > if (compute_effective_progs(cgrp, i, &arrays[i])) > @@ -2759,3 +2777,31 @@ cgroup_common_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) > return NULL; > } > } > + > +int cgroup_bpf_attach_struct_ops(struct cgroup *cgrp, > + struct bpf_struct_ops_link *link) > +{ > + int ret = 0; > + > + cgroup_lock(); > + if (percpu_ref_is_zero(&cgrp->bpf.refcnt)) { > + ret = -EBUSY; If the cgroup is dying, then perhaps -EINVAL would be more appropriate here, no? I'd argue that -EBUSY implies a temporary or transient state. > + goto out; > + } > + list_add_tail(&link->list, &cgrp->bpf.struct_ops_links); > +out: > + cgroup_unlock(); > + return ret; > +} > + > +void cgroup_bpf_detach_struct_ops(struct cgroup *cgrp, > + struct bpf_struct_ops_link *link) > +{ > + cgroup_lock(); > + if (link->cgroup == cgrp) { > + list_del(&link->list); > + link->cgroup = NULL; > + cgroup_put(cgrp); > + } > + cgroup_unlock(); > +} Within cgroup_bpf_attach_struct_ops() and cgroup_bpf_detach_struct_ops() the cgrp pointer appears to be superfluous? Both should probably only operate on link->cgroup instead? A !link->cgroup when calling either should be considered as -EINVAL. > diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h > index 3ca7d76e05f0..d5492e60744a 100644 > --- a/tools/include/uapi/linux/bpf.h > +++ b/tools/include/uapi/linux/bpf.h > @@ -1237,6 +1237,7 @@ enum bpf_perf_event_type { > #define BPF_F_AFTER (1U << 4) > #define BPF_F_ID (1U << 5) > #define BPF_F_PREORDER (1U << 6) > +#define BPF_F_CGROUP_FD (1U << 7) > #define BPF_F_LINK BPF_F_LINK /* 1 << 13 */ > > /* If BPF_F_STRICT_ALIGNMENT is used in BPF_PROG_LOAD command, the > -- > 2.52.0 >