Re: [PATCH bpf-next 2/5] bpf: Implement cgroup storage available to non-cgroup-attached bpf progs

Stanislav Fomichev
2022-10-17T18:43:45Z

On Mon, Oct 17, 2022 at 11:26 AM Yosry Ahmed <yosryahmed@google.com> wrote:
>
> On Mon, Oct 17, 2022 at 11:02 AM <sdf@google.com> wrote:
> >
> > On 10/13, Yonghong Song wrote:
> > > Similar to sk/inode/task storage, implement similar cgroup local storage.
> >
> > > There already exists a local storage implementation for cgroup-attached
> > > bpf programs. See map type BPF_MAP_TYPE_CGROUP_STORAGE and helper
> > > bpf_get_local_storage(). But there are use cases such that non-cgroup
> > > attached bpf progs wants to access cgroup local storage data. For example,
> > > tc egress prog has access to sk and cgroup. It is possible to use
> > > sk local storage to emulate cgroup local storage by storing data in
> > > socket.
> > > But this is a waste as it could be lots of sockets belonging to a
> > > particular
> > > cgroup. Alternatively, a separate map can be created with cgroup id as
> > > the key.
> > > But this will introduce additional overhead to manipulate the new map.
> > > A cgroup local storage, similar to existing sk/inode/task storage,
> > > should help for this use case.
> >
> > > The life-cycle of storage is managed with the life-cycle of the
> > > cgroup struct. i.e. the storage is destroyed along with the owning cgroup
> > > with a callback to the bpf_cgroup_storage_free when cgroup itself
> > > is deleted.
> >
> > > The userspace map operations can be done by using a cgroup fd as a key
> > > passed to the lookup, update and delete operations.
> >
> >
> > [..]
> >
> > > Since map name BPF_MAP_TYPE_CGROUP_STORAGE has been used for old cgroup
> > > local
> > > storage support, the new map name BPF_MAP_TYPE_CGROUP_LOCAL_STORAGE is
> > > used
> > > for cgroup storage available to non-cgroup-attached bpf programs. The two
> > > helpers are named as bpf_cgroup_local_storage_get() and
> > > bpf_cgroup_local_storage_delete().
> >
> > Have you considered doing something similar to 7d9c3427894f ("bpf: Make
> > cgroup storages shared between programs on the same cgroup") where
> > the map changes its behavior depending on the key size (see key_size checks
> > in cgroup_storage_map_alloc)? Looks like sizeof(int) for fd still
> > can be used so we can, in theory, reuse the name..
> >
> > Pros:
> > - no need for a new map name
> >
> > Cons:
> > - existing BPF_MAP_TYPE_CGROUP_STORAGE is already messy; might be not a
> > good idea to add more stuff to it?
> >
> > But, for the very least, should we also extend
> > Documentation/bpf/map_cgroup_storage.rst to cover the new map? We've
> > tried to keep some of the important details in there..
>
> This might be a long shot, but is it possible to switch completely to
> this new generic cgroup storage, and for programs that attach to
> cgroups we can still do lookups/allocations during attachment like we
> do today? IOW, maintain the current API for cgroup progs but switch it
> to use this new map type instead.
>
> It feels like this map type is more generic and can be a superset of
> the existing cgroup storage, but I feel like I am missing something.

I feel like the biggest issue is that the existing
bpf_get_local_storage helper is guaranteed to always return non-null
and the verifier doesn't require the programs to do null checks on it;
the new helper might return NULL making all existing programs fail the
verifier.

There might be something else I don't remember at this point (besides
that weird per-prog_type that we'd have to emulate as well)..

> >
> > > Signed-off-by: Yonghong Song <yhs@fb.com>
> > > ---
> > > include/linux/bpf.h | 3 +
> > > include/linux/bpf_types.h | 1 +
> > > include/linux/cgroup-defs.h | 4 +
> > > include/uapi/linux/bpf.h | 39 +++++
> > > kernel/bpf/Makefile | 2 +-
> > > kernel/bpf/bpf_cgroup_storage.c | 280 ++++++++++++++++++++++++++++++++
> > > kernel/bpf/helpers.c | 6 +
> > > kernel/bpf/syscall.c | 3 +-
> > > kernel/bpf/verifier.c | 14 +-
> > > kernel/cgroup/cgroup.c | 4 +
> > > kernel/trace/bpf_trace.c | 4 +
> > > scripts/bpf_doc.py | 2 +
> > > tools/include/uapi/linux/bpf.h | 39 +++++
> > > 13 files changed, 398 insertions(+), 3 deletions(-)
> > > create mode 100644 kernel/bpf/bpf_cgroup_storage.c
> >
> > > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > > index 9e7d46d16032..1395a01c7f18 100644
> > > --- a/include/linux/bpf.h
> > > +++ b/include/linux/bpf.h
> > > @@ -2045,6 +2045,7 @@ struct bpf_link *bpf_link_by_id(u32 id);
> >
> > > const struct bpf_func_proto *bpf_base_func_proto(enum bpf_func_id
> > > func_id);
> > > void bpf_task_storage_free(struct task_struct *task);
> > > +void bpf_local_cgroup_storage_free(struct cgroup *cgroup);
> > > bool bpf_prog_has_kfunc_call(const struct bpf_prog *prog);
> > > const struct btf_func_model *
> > > bpf_jit_find_kfunc_model(const struct bpf_prog *prog,
> > > @@ -2537,6 +2538,8 @@ extern const struct bpf_func_proto
> > > bpf_copy_from_user_task_proto;
> > > extern const struct bpf_func_proto bpf_set_retval_proto;
> > > extern const struct bpf_func_proto bpf_get_retval_proto;
> > > extern const struct bpf_func_proto bpf_user_ringbuf_drain_proto;
> > > +extern const struct bpf_func_proto bpf_cgroup_storage_get_proto;
> > > +extern const struct bpf_func_proto bpf_cgroup_storage_delete_proto;
> >
> > > const struct bpf_func_proto *tracing_prog_func_proto(
> > > enum bpf_func_id func_id, const struct bpf_prog *prog);
> > > diff --git a/include/linux/bpf_types.h b/include/linux/bpf_types.h
> > > index 2c6a4f2562a7..7a0362d7a0aa 100644
> > > --- a/include/linux/bpf_types.h
> > > +++ b/include/linux/bpf_types.h
> > > @@ -90,6 +90,7 @@ BPF_MAP_TYPE(BPF_MAP_TYPE_CGROUP_ARRAY,
> > > cgroup_array_map_ops)
> > > #ifdef CONFIG_CGROUP_BPF
> > > BPF_MAP_TYPE(BPF_MAP_TYPE_CGROUP_STORAGE, cgroup_storage_map_ops)
> > > BPF_MAP_TYPE(BPF_MAP_TYPE_PERCPU_CGROUP_STORAGE, cgroup_storage_map_ops)
> > > +BPF_MAP_TYPE(BPF_MAP_TYPE_CGROUP_LOCAL_STORAGE,
> > > cgroup_local_storage_map_ops)
> > > #endif
> > > BPF_MAP_TYPE(BPF_MAP_TYPE_HASH, htab_map_ops)
> > > BPF_MAP_TYPE(BPF_MAP_TYPE_PERCPU_HASH, htab_percpu_map_ops)
> > > diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
> > > index 4bcf56b3491c..c6f4590dda68 100644
> > > --- a/include/linux/cgroup-defs.h
> > > +++ b/include/linux/cgroup-defs.h
> > > @@ -504,6 +504,10 @@ struct cgroup {
> > > /* Used to store internal freezer state */
> > > struct cgroup_freezer_state freezer;
> >
> > > +#ifdef CONFIG_BPF_SYSCALL
> > > + struct bpf_local_storage __rcu *bpf_cgroup_storage;
> > > +#endif
> > > +
> > > /* ids of the ancestors at each level including self */
> > > u64 ancestor_ids[];
> > > };
> > > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> > > index 17f61338f8f8..d918b4054297 100644
> > > --- a/include/uapi/linux/bpf.h
> > > +++ b/include/uapi/linux/bpf.h
> > > @@ -935,6 +935,7 @@ enum bpf_map_type {
> > > BPF_MAP_TYPE_TASK_STORAGE,
> > > BPF_MAP_TYPE_BLOOM_FILTER,
> > > BPF_MAP_TYPE_USER_RINGBUF,
> > > + BPF_MAP_TYPE_CGROUP_LOCAL_STORAGE,
> > > };
> >
> > > /* Note that tracing related programs such as
> > > @@ -5435,6 +5436,42 @@ union bpf_attr {
> > > * **-E2BIG** if user-space has tried to publish a sample which is
> > > * larger than the size of the ring buffer, or which cannot fit
> > > * within a struct bpf_dynptr.
> > > + *
> > > + * void *bpf_cgroup_local_storage_get(struct bpf_map *map, struct cgroup
> > > *cgroup, void *value, u64 flags)
> > > + * Description
> > > + * Get a bpf_local_storage from the *cgroup*.
> > > + *
> > > + * Logically, it could be thought of as getting the value from
> > > + * a *map* with *cgroup* as the **key**. From this
> > > + * perspective, the usage is not much different from
> > > + * **bpf_map_lookup_elem**\ (*map*, **&**\ *cgroup*) except this
> > > + * helper enforces the key must be a cgroup struct and the map must also
> > > + * be a **BPF_MAP_TYPE_CGROUP_LOCAL_STORAGE**.
> > > + *
> > > + * Underneath, the value is stored locally at *cgroup* instead of
> > > + * the *map*. The *map* is used as the bpf-local-storage
> > > + * "type". The bpf-local-storage "type" (i.e. the *map*) is
> > > + * searched against all bpf_local_storage residing at *cgroup*.
> > > + *
> > > + * An optional *flags* (**BPF_LOCAL_STORAGE_GET_F_CREATE**) can be
> > > + * used such that a new bpf_local_storage will be
> > > + * created if one does not exist. *value* can be used
> > > + * together with **BPF_LOCAL_STORAGE_GET_F_CREATE** to specify
> > > + * the initial value of a bpf_local_storage. If *value* is
> > > + * **NULL**, the new bpf_local_storage will be zero initialized.
> > > + * Return
> > > + * A bpf_local_storage pointer is returned on success.
> > > + *
> > > + * **NULL** if not found or there was an error in adding
> > > + * a new bpf_local_storage.
> > > + *
> > > + * long bpf_cgroup_local_storage_delete(struct bpf_map *map, struct
> > > cgroup *cgroup)
> > > + * Description
> > > + * Delete a bpf_local_storage from a *cgroup*.
> > > + * Return
> > > + * 0 on success.
> > > + *
> > > + * **-ENOENT** if the bpf_local_storage cannot be found.
> > > */
> > > #define ___BPF_FUNC_MAPPER(FN, ctx...) \
> > > FN(unspec, 0, ##ctx) \
> > > @@ -5647,6 +5684,8 @@ union bpf_attr {
> > > FN(tcp_raw_check_syncookie_ipv6, 207, ##ctx) \
> > > FN(ktime_get_tai_ns, 208, ##ctx) \
> > > FN(user_ringbuf_drain, 209, ##ctx) \
> > > + FN(cgroup_local_storage_get, 210, ##ctx) \
> > > + FN(cgroup_local_storage_delete, 211, ##ctx) \
> > > /* */
> >
> > > /* backwards-compatibility macros for users of __BPF_FUNC_MAPPER that
> > > don't
> > > diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
> > > index 341c94f208f4..b02693f51978 100644
> > > --- a/kernel/bpf/Makefile
> > > +++ b/kernel/bpf/Makefile
> > > @@ -25,7 +25,7 @@ ifeq ($(CONFIG_PERF_EVENTS),y)
> > > obj-$(CONFIG_BPF_SYSCALL) += stackmap.o
> > > endif
> > > ifeq ($(CONFIG_CGROUPS),y)
> > > -obj-$(CONFIG_BPF_SYSCALL) += cgroup_iter.o
> > > +obj-$(CONFIG_BPF_SYSCALL) += cgroup_iter.o bpf_cgroup_storage.o
> > > endif
> > > obj-$(CONFIG_CGROUP_BPF) += cgroup.o
> > > ifeq ($(CONFIG_INET),y)
> > > diff --git a/kernel/bpf/bpf_cgroup_storage.c
> > > b/kernel/bpf/bpf_cgroup_storage.c
> > > new file mode 100644
> > > index 000000000000..9974784822da
> > > --- /dev/null
> > > +++ b/kernel/bpf/bpf_cgroup_storage.c
> > > @@ -0,0 +1,280 @@
> > > +// SPDX-License-Identifier: GPL-2.0
> > > +/*
> > > + * Copyright (c) 2022 Meta Platforms, Inc. and affiliates.
> > > + */
> > > +
> > > +#include <linux/types.h>
> > > +#include <linux/bpf.h>
> > > +#include <linux/bpf_local_storage.h>
> > > +#include <uapi/linux/btf.h>
> > > +#include <linux/btf_ids.h>
> > > +
> > > +DEFINE_BPF_STORAGE_CACHE(cgroup_cache);
> > > +
> > > +static DEFINE_PER_CPU(int, bpf_cgroup_storage_busy);
> > > +
> > > +static void bpf_cgroup_storage_lock(void)
> > > +{
> > > + migrate_disable();
> > > + this_cpu_inc(bpf_cgroup_storage_busy);
> > > +}
> > > +
> > > +static void bpf_cgroup_storage_unlock(void)
> > > +{
> > > + this_cpu_dec(bpf_cgroup_storage_busy);
> > > + migrate_enable();
> > > +}
> > > +
> > > +static bool bpf_cgroup_storage_trylock(void)
> > > +{
> > > + migrate_disable();
> > > + if (unlikely(this_cpu_inc_return(bpf_cgroup_storage_busy) != 1)) {
> > > + this_cpu_dec(bpf_cgroup_storage_busy);
> > > + migrate_enable();
> > > + return false;
> > > + }
> > > + return true;
> > > +}
> >
> > Task storage has lock/unlock/trylock; inode storage doesn't; why does
> > cgroup need it as well?
> >
> > > +static struct bpf_local_storage __rcu **cgroup_storage_ptr(void *owner)
> > > +{
> > > + struct cgroup *cg = owner;
> > > +
> > > + return &cg->bpf_cgroup_storage;
> > > +}
> > > +
> > > +void bpf_local_cgroup_storage_free(struct cgroup *cgroup)
> > > +{
> > > + struct bpf_local_storage *local_storage;
> > > + struct bpf_local_storage_elem *selem;
> > > + bool free_cgroup_storage = false;
> > > + struct hlist_node *n;
> > > + unsigned long flags;
> > > +
> > > + rcu_read_lock();
> > > + local_storage = rcu_dereference(cgroup->bpf_cgroup_storage);
> > > + if (!local_storage) {
> > > + rcu_read_unlock();
> > > + return;
> > > + }
> > > +
> > > + /* Neither the bpf_prog nor the bpf-map's syscall
> > > + * could be modifying the local_storage->list now.
> > > + * Thus, no elem can be added-to or deleted-from the
> > > + * local_storage->list by the bpf_prog or by the bpf-map's syscall.
> > > + *
> > > + * It is racing with bpf_local_storage_map_free() alone
> > > + * when unlinking elem from the local_storage->list and
> > > + * the map's bucket->list.
> > > + */
> > > + bpf_cgroup_storage_lock();
> > > + raw_spin_lock_irqsave(&local_storage->lock, flags);
> > > + hlist_for_each_entry_safe(selem, n, &local_storage->list, snode) {
> > > + bpf_selem_unlink_map(selem);
> > > + free_cgroup_storage =
> > > + bpf_selem_unlink_storage_nolock(local_storage, selem, false, false);
> > > + }
> > > + raw_spin_unlock_irqrestore(&local_storage->lock, flags);
> > > + bpf_cgroup_storage_unlock();
> > > + rcu_read_unlock();
> > > +
> > > + /* free_cgroup_storage should always be true as long as
> > > + * local_storage->list was non-empty.
> > > + */
> > > + if (free_cgroup_storage)
> > > + kfree_rcu(local_storage, rcu);
> > > +}
> >
> > > +static struct bpf_local_storage_data *
> > > +cgroup_storage_lookup(struct cgroup *cgroup, struct bpf_map *map, bool
> > > cacheit_lockit)
> > > +{
> > > + struct bpf_local_storage *cgroup_storage;
> > > + struct bpf_local_storage_map *smap;
> > > +
> > > + cgroup_storage = rcu_dereference_check(cgroup->bpf_cgroup_storage,
> > > + bpf_rcu_lock_held());
> > > + if (!cgroup_storage)
> > > + return NULL;
> > > +
> > > + smap = (struct bpf_local_storage_map *)map;
> > > + return bpf_local_storage_lookup(cgroup_storage, smap, cacheit_lockit);
> > > +}
> > > +
> > > +static void *bpf_cgroup_storage_lookup_elem(struct bpf_map *map, void
> > > *key)
> > > +{
> > > + struct bpf_local_storage_data *sdata;
> > > + struct cgroup *cgroup;
> > > + int fd;
> > > +
> > > + fd = *(int *)key;
> > > + cgroup = cgroup_get_from_fd(fd);
> > > + if (IS_ERR(cgroup))
> > > + return ERR_CAST(cgroup);
> > > +
> > > + bpf_cgroup_storage_lock();
> > > + sdata = cgroup_storage_lookup(cgroup, map, true);
> > > + bpf_cgroup_storage_unlock();
> > > + cgroup_put(cgroup);
> > > + return sdata ? sdata->data : NULL;
> > > +}
> >
> > A lot of the above (free/lookup) seems to be copy-pasted from the task
> > storage;
> > any point in trying to generalize the common parts?
> >
> > > +static int bpf_cgroup_storage_update_elem(struct bpf_map *map, void *key,
> > > + void *value, u64 map_flags)
> > > +{
> > > + struct bpf_local_storage_data *sdata;
> > > + struct cgroup *cgroup;
> > > + int err, fd;
> > > +
> > > + fd = *(int *)key;
> > > + cgroup = cgroup_get_from_fd(fd);
> > > + if (IS_ERR(cgroup))
> > > + return PTR_ERR(cgroup);
> > > +
> > > + bpf_cgroup_storage_lock();
> > > + sdata = bpf_local_storage_update(cgroup, (struct bpf_local_storage_map
> > > *)map,
> > > + value, map_flags, GFP_ATOMIC);
> > > + bpf_cgroup_storage_unlock();
> > > + err = PTR_ERR_OR_ZERO(sdata);
> > > + cgroup_put(cgroup);
> > > + return err;
> > > +}
> > > +
> > > +static int cgroup_storage_delete(struct cgroup *cgroup, struct bpf_map
> > > *map)
> > > +{
> > > + struct bpf_local_storage_data *sdata;
> > > +
> > > + sdata = cgroup_storage_lookup(cgroup, map, false);
> > > + if (!sdata)
> > > + return -ENOENT;
> > > +
> > > + bpf_selem_unlink(SELEM(sdata), true);
> > > + return 0;
> > > +}
> > > +
> > > +static int bpf_cgroup_storage_delete_elem(struct bpf_map *map, void *key)
> > > +{
> > > + struct cgroup *cgroup;
> > > + int err, fd;
> > > +
> > > + fd = *(int *)key;
> > > + cgroup = cgroup_get_from_fd(fd);
> > > + if (IS_ERR(cgroup))
> > > + return PTR_ERR(cgroup);
> > > +
> > > + bpf_cgroup_storage_lock();
> > > + err = cgroup_storage_delete(cgroup, map);
> > > + bpf_cgroup_storage_unlock();
> > > + if (err)
> > > + return err;
> > > +
> > > + cgroup_put(cgroup);
> > > + return 0;
> > > +}
> > > +
> > > +static int notsupp_get_next_key(struct bpf_map *map, void *key, void
> > > *next_key)
> > > +{
> > > + return -ENOTSUPP;
> > > +}
> > > +
> > > +static struct bpf_map *cgroup_storage_map_alloc(union bpf_attr *attr)
> > > +{
> > > + struct bpf_local_storage_map *smap;
> > > +
> > > + smap = bpf_local_storage_map_alloc(attr);
> > > + if (IS_ERR(smap))
> > > + return ERR_CAST(smap);
> > > +
> > > + smap->cache_idx = bpf_local_storage_cache_idx_get(&cgroup_cache);
> > > + return &smap->map;
> > > +}
> > > +
> > > +static void cgroup_storage_map_free(struct bpf_map *map)
> > > +{
> > > + struct bpf_local_storage_map *smap;
> > > +
> > > + smap = (struct bpf_local_storage_map *)map;
> > > + bpf_local_storage_cache_idx_free(&cgroup_cache, smap->cache_idx);
> > > + bpf_local_storage_map_free(smap, NULL);
> > > +}
> > > +
> > > +/* *gfp_flags* is a hidden argument provided by the verifier */
> > > +BPF_CALL_5(bpf_cgroup_storage_get, struct bpf_map *, map, struct cgroup
> > > *, cgroup,
> > > + void *, value, u64, flags, gfp_t, gfp_flags)
> > > +{
> > > + struct bpf_local_storage_data *sdata;
> > > +
> > > + WARN_ON_ONCE(!bpf_rcu_lock_held());
> > > + if (flags & ~(BPF_LOCAL_STORAGE_GET_F_CREATE))
> > > + return (unsigned long)NULL;
> > > +
> > > + if (!cgroup)
> > > + return (unsigned long)NULL;
> > > +
> > > + if (!bpf_cgroup_storage_trylock())
> > > + return (unsigned long)NULL;
> > > +
> > > + sdata = cgroup_storage_lookup(cgroup, map, true);
> > > + if (sdata)
> > > + goto unlock;
> > > +
> > > + /* only allocate new storage, when the cgroup is refcounted */
> > > + if (!percpu_ref_is_dying(&cgroup->self.refcnt) &&
> > > + (flags & BPF_LOCAL_STORAGE_GET_F_CREATE))
> > > + sdata = bpf_local_storage_update(cgroup, (struct bpf_local_storage_map
> > > *)map,
> > > + value, BPF_NOEXIST, gfp_flags);
> > > +
> > > +unlock:
> > > + bpf_cgroup_storage_unlock();
> > > + return IS_ERR_OR_NULL(sdata) ? (unsigned long)NULL : (unsigned
> > > long)sdata->data;
> > > +}
> > > +
> > > +BPF_CALL_2(bpf_cgroup_storage_delete, struct bpf_map *, map, struct
> > > cgroup *, cgroup)
> > > +{
> > > + int ret;
> > > +
> > > + WARN_ON_ONCE(!bpf_rcu_lock_held());
> > > + if (!cgroup)
> > > + return -EINVAL;
> > > +
> > > + if (!bpf_cgroup_storage_trylock())
> > > + return -EBUSY;
> > > +
> > > + ret = cgroup_storage_delete(cgroup, map);
> > > + bpf_cgroup_storage_unlock();
> > > + return ret;
> > > +}
> > > +
> > > +BTF_ID_LIST_SINGLE(cgroup_storage_map_btf_ids, struct,
> > > bpf_local_storage_map)
> > > +const struct bpf_map_ops cgroup_local_storage_map_ops = {
> > > + .map_meta_equal = bpf_map_meta_equal,
> > > + .map_alloc_check = bpf_local_storage_map_alloc_check,
> > > + .map_alloc = cgroup_storage_map_alloc,
> > > + .map_free = cgroup_storage_map_free,
> > > + .map_get_next_key = notsupp_get_next_key,
> > > + .map_lookup_elem = bpf_cgroup_storage_lookup_elem,
> > > + .map_update_elem = bpf_cgroup_storage_update_elem,
> > > + .map_delete_elem = bpf_cgroup_storage_delete_elem,
> > > + .map_check_btf = bpf_local_storage_map_check_btf,
> > > + .map_btf_id = &cgroup_storage_map_btf_ids[0],
> > > + .map_owner_storage_ptr = cgroup_storage_ptr,
> > > +};
> > > +
> > > +const struct bpf_func_proto bpf_cgroup_storage_get_proto = {
> > > + .func = bpf_cgroup_storage_get,
> > > + .gpl_only = false,
> > > + .ret_type = RET_PTR_TO_MAP_VALUE_OR_NULL,
> > > + .arg1_type = ARG_CONST_MAP_PTR,
> > > + .arg2_type = ARG_PTR_TO_BTF_ID,
> > > + .arg2_btf_id = &bpf_cgroup_btf_id[0],
> > > + .arg3_type = ARG_PTR_TO_MAP_VALUE_OR_NULL,
> > > + .arg4_type = ARG_ANYTHING,
> > > +};
> > > +
> > > +const struct bpf_func_proto bpf_cgroup_storage_delete_proto = {
> > > + .func = bpf_cgroup_storage_delete,
> > > + .gpl_only = false,
> > > + .ret_type = RET_INTEGER,
> > > + .arg1_type = ARG_CONST_MAP_PTR,
> > > + .arg2_type = ARG_PTR_TO_BTF_ID,
> > > + .arg2_btf_id = &bpf_cgroup_btf_id[0],
> > > +};
> > > diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> > > index a6b04faed282..5c5bb08832ec 100644
> > > --- a/kernel/bpf/helpers.c
> > > +++ b/kernel/bpf/helpers.c
> > > @@ -1663,6 +1663,12 @@ bpf_base_func_proto(enum bpf_func_id func_id)
> > > return &bpf_dynptr_write_proto;
> > > case BPF_FUNC_dynptr_data:
> > > return &bpf_dynptr_data_proto;
> > > +#ifdef CONFIG_CGROUPS
> > > + case BPF_FUNC_cgroup_local_storage_get:
> > > + return &bpf_cgroup_storage_get_proto;
> > > + case BPF_FUNC_cgroup_local_storage_delete:
> > > + return &bpf_cgroup_storage_delete_proto;
> > > +#endif
> > > default:
> > > break;
> > > }
> > > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> > > index 7b373a5e861f..e53c7fae6e22 100644
> > > --- a/kernel/bpf/syscall.c
> > > +++ b/kernel/bpf/syscall.c
> > > @@ -1016,7 +1016,8 @@ static int map_check_btf(struct bpf_map *map, const
> > > struct btf *btf,
> > > map->map_type != BPF_MAP_TYPE_CGROUP_STORAGE &&
> > > map->map_type != BPF_MAP_TYPE_SK_STORAGE &&
> > > map->map_type != BPF_MAP_TYPE_INODE_STORAGE &&
> > > - map->map_type != BPF_MAP_TYPE_TASK_STORAGE)
> > > + map->map_type != BPF_MAP_TYPE_TASK_STORAGE &&
> > > + map->map_type != BPF_MAP_TYPE_CGROUP_LOCAL_STORAGE)
> > > return -ENOTSUPP;
> > > if (map->spin_lock_off + sizeof(struct bpf_spin_lock) >
> > > map->value_size) {
> > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > > index 6f6d2d511c06..f36f6a3c0d50 100644
> > > --- a/kernel/bpf/verifier.c
> > > +++ b/kernel/bpf/verifier.c
> > > @@ -6360,6 +6360,11 @@ static int check_map_func_compatibility(struct
> > > bpf_verifier_env *env,
> > > func_id != BPF_FUNC_task_storage_delete)
> > > goto error;
> > > break;
> > > + case BPF_MAP_TYPE_CGROUP_LOCAL_STORAGE:
> > > + if (func_id != BPF_FUNC_cgroup_local_storage_get &&
> > > + func_id != BPF_FUNC_cgroup_local_storage_delete)
> > > + goto error;
> > > + break;
> > > case BPF_MAP_TYPE_BLOOM_FILTER:
> > > if (func_id != BPF_FUNC_map_peek_elem &&
> > > func_id != BPF_FUNC_map_push_elem)
> > > @@ -6472,6 +6477,11 @@ static int check_map_func_compatibility(struct
> > > bpf_verifier_env *env,
> > > if (map->map_type != BPF_MAP_TYPE_TASK_STORAGE)
> > > goto error;
> > > break;
> > > + case BPF_FUNC_cgroup_local_storage_get:
> > > + case BPF_FUNC_cgroup_local_storage_delete:
> > > + if (map->map_type != BPF_MAP_TYPE_CGROUP_LOCAL_STORAGE)
> > > + goto error;
> > > + break;
> > > default:
> > > break;
> > > }
> > > @@ -12713,6 +12723,7 @@ static int check_map_prog_compatibility(struct
> > > bpf_verifier_env *env,
> > > case BPF_MAP_TYPE_INODE_STORAGE:
> > > case BPF_MAP_TYPE_SK_STORAGE:
> > > case BPF_MAP_TYPE_TASK_STORAGE:
> > > + case BPF_MAP_TYPE_CGROUP_LOCAL_STORAGE:
> > > break;
> > > default:
> > > verbose(env,
> > > @@ -14149,7 +14160,8 @@ static int do_misc_fixups(struct bpf_verifier_env
> > > *env)
> >
> > > if (insn->imm == BPF_FUNC_task_storage_get ||
> > > insn->imm == BPF_FUNC_sk_storage_get ||
> > > - insn->imm == BPF_FUNC_inode_storage_get) {
> > > + insn->imm == BPF_FUNC_inode_storage_get ||
> > > + insn->imm == BPF_FUNC_cgroup_local_storage_get) {
> > > if (env->prog->aux->sleepable)
> > > insn_buf[0] = BPF_MOV64_IMM(BPF_REG_5, (__force __s32)GFP_KERNEL);
> > > else
> > > diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
> > > index 8ad2c267ff47..2fa2c950c7fb 100644
> > > --- a/kernel/cgroup/cgroup.c
> > > +++ b/kernel/cgroup/cgroup.c
> > > @@ -985,6 +985,10 @@ void put_css_set_locked(struct css_set *cset)
> > > put_css_set_locked(cset->dom_cset);
> > > }
> >
> > > +#ifdef CONFIG_BPF_SYSCALL
> > > + bpf_local_cgroup_storage_free(cset->dfl_cgrp);
> > > +#endif
> > > +
>
> I am confused about this freeing site. It seems like this path is for
> freeing css_set's of task_structs, not for freeing the cgroup itself.
> Wouldn't we want to free the local storage when we free the cgroup
> itself? Somewhere like css_free_rwork_fn()? or did I completely miss
> the point here?
>
> > > kfree_rcu(cset, rcu_head);
> > > }
> >
> > > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> > > index 688552df95ca..179adaae4a9f 100644
> > > --- a/kernel/trace/bpf_trace.c
> > > +++ b/kernel/trace/bpf_trace.c
> > > @@ -1454,6 +1454,10 @@ bpf_tracing_func_proto(enum bpf_func_id func_id,
> > > const struct bpf_prog *prog)
> > > return &bpf_get_current_cgroup_id_proto;
> > > case BPF_FUNC_get_current_ancestor_cgroup_id:
> > > return &bpf_get_current_ancestor_cgroup_id_proto;
> > > + case BPF_FUNC_cgroup_local_storage_get:
> > > + return &bpf_cgroup_storage_get_proto;
> > > + case BPF_FUNC_cgroup_local_storage_delete:
> > > + return &bpf_cgroup_storage_delete_proto;
> > > #endif
> > > case BPF_FUNC_send_signal:
> > > return &bpf_send_signal_proto;
> > > diff --git a/scripts/bpf_doc.py b/scripts/bpf_doc.py
> > > index c0e6690be82a..fdb0aff8cb5a 100755
> > > --- a/scripts/bpf_doc.py
> > > +++ b/scripts/bpf_doc.py
> > > @@ -685,6 +685,7 @@ class PrinterHelpers(Printer):
> > > 'struct udp6_sock',
> > > 'struct unix_sock',
> > > 'struct task_struct',
> > > + 'struct cgroup',
> >
> > > 'struct __sk_buff',
> > > 'struct sk_msg_md',
> > > @@ -742,6 +743,7 @@ class PrinterHelpers(Printer):
> > > 'struct udp6_sock',
> > > 'struct unix_sock',
> > > 'struct task_struct',
> > > + 'struct cgroup',
> > > 'struct path',
> > > 'struct btf_ptr',
> > > 'struct inode',
> > > diff --git a/tools/include/uapi/linux/bpf.h
> > > b/tools/include/uapi/linux/bpf.h
> > > index 17f61338f8f8..d918b4054297 100644
> > > --- a/tools/include/uapi/linux/bpf.h
> > > +++ b/tools/include/uapi/linux/bpf.h
> > > @@ -935,6 +935,7 @@ enum bpf_map_type {
> > > BPF_MAP_TYPE_TASK_STORAGE,
> > > BPF_MAP_TYPE_BLOOM_FILTER,
> > > BPF_MAP_TYPE_USER_RINGBUF,
> > > + BPF_MAP_TYPE_CGROUP_LOCAL_STORAGE,
> > > };
> >
> > > /* Note that tracing related programs such as
> > > @@ -5435,6 +5436,42 @@ union bpf_attr {
> > > * **-E2BIG** if user-space has tried to publish a sample which is
> > > * larger than the size of the ring buffer, or which cannot fit
> > > * within a struct bpf_dynptr.
> > > + *
> > > + * void *bpf_cgroup_local_storage_get(struct bpf_map *map, struct cgroup
> > > *cgroup, void *value, u64 flags)
> > > + * Description
> > > + * Get a bpf_local_storage from the *cgroup*.
> > > + *
> > > + * Logically, it could be thought of as getting the value from
> > > + * a *map* with *cgroup* as the **key**. From this
> > > + * perspective, the usage is not much different from
> > > + * **bpf_map_lookup_elem**\ (*map*, **&**\ *cgroup*) except this
> > > + * helper enforces the key must be a cgroup struct and the map must also
> > > + * be a **BPF_MAP_TYPE_CGROUP_LOCAL_STORAGE**.
> > > + *
> > > + * Underneath, the value is stored locally at *cgroup* instead of
> > > + * the *map*. The *map* is used as the bpf-local-storage
> > > + * "type". The bpf-local-storage "type" (i.e. the *map*) is
> > > + * searched against all bpf_local_storage residing at *cgroup*.
> > > + *
> > > + * An optional *flags* (**BPF_LOCAL_STORAGE_GET_F_CREATE**) can be
> > > + * used such that a new bpf_local_storage will be
> > > + * created if one does not exist. *value* can be used
> > > + * together with **BPF_LOCAL_STORAGE_GET_F_CREATE** to specify
> > > + * the initial value of a bpf_local_storage. If *value* is
> > > + * **NULL**, the new bpf_local_storage will be zero initialized.
> > > + * Return
> > > + * A bpf_local_storage pointer is returned on success.
> > > + *
> > > + * **NULL** if not found or there was an error in adding
> > > + * a new bpf_local_storage.
> > > + *
> > > + * long bpf_cgroup_local_storage_delete(struct bpf_map *map, struct
> > > cgroup *cgroup)
> > > + * Description
> > > + * Delete a bpf_local_storage from a *cgroup*.
> > > + * Return
> > > + * 0 on success.
> > > + *
> > > + * **-ENOENT** if the bpf_local_storage cannot be found.
> > > */
> > > #define ___BPF_FUNC_MAPPER(FN, ctx...) \
> > > FN(unspec, 0, ##ctx) \
> > > @@ -5647,6 +5684,8 @@ union bpf_attr {
> > > FN(tcp_raw_check_syncookie_ipv6, 207, ##ctx) \
> > > FN(ktime_get_tai_ns, 208, ##ctx) \
> > > FN(user_ringbuf_drain, 209, ##ctx) \
> > > + FN(cgroup_local_storage_get, 210, ##ctx) \
> > > + FN(cgroup_local_storage_delete, 211, ##ctx) \
> > > /* */
> >
> > > /* backwards-compatibility macros for users of __BPF_FUNC_MAPPER that
> > > don't
> > > --
> > > 2.30.2
> >