Message-ID: <9452fd5c-af81-3764-4c90-052235f1bb7d@fb.com>
Date:   Fri, 26 Apr 2019 17:27:16 +0000
From:   Yonghong Song <yhs@...com>
To:     Martin Lau <kafai@...com>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     Alexei Starovoitov <ast@...com>, Andrii Nakryiko <andriin@...com>,
        "Daniel Borkmann" <daniel@...earbox.net>,
        John Fastabend <john.fastabend@...il.com>,
        Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH v2 bpf-next 1/6] bpf: Introduce bpf sk local storage



On 4/25/19 5:10 PM, Martin KaFai Lau wrote:
> After allowing a bpf prog to
> - directly read the skb->sk ptr
> - get the fullsock bpf_sock by "bpf_sk_fullsock()"
> - get the bpf_tcp_sock by "bpf_tcp_sock()"
> - get the listener sock by "bpf_get_listener_sock()"
> - avoid duplicating the fields of "(bpf_)sock" and "(bpf_)tcp_sock"
>    into different bpf running context.
> 
> this patch is another effort to make bpf's network programming
> more intuitive to do (together with memory and performance benefit).
> 
> When bpf prog needs to store data for a sk, the current practice is to
> define a map with the usual 4-tuples (src/dst ip/port) as the key.
> If multiple bpf progs require to store different sk data, multiple maps
> have to be defined.  Hence, wasting memory to store the duplicated
> keys (i.e. 4 tuples here) in each of the bpf map.
> [ The smallest key could be the sk pointer itself which requires
>    some enhancement in the verifier and it is a separate topic. ]
> 
> Also, the bpf prog needs to clean up the elem when sk is freed.
> Otherwise, the bpf map will become full and un-usable quickly.
> The sk-free tracking currently could be done during sk state
> transition (e.g. BPF_SOCK_OPS_STATE_CB).
> 
> The size of the map needs to be predefined which then usually ended-up
> with an over-provisioned map in production.  Even the map was re-sizable,
> while the sk naturally come and go away already, this potential re-size
> operation is arguably redundant if the data can be directly connected
> to the sk itself instead of proxy-ing through a bpf map.
> 
> This patch introduces sk->sk_bpf_storage to provide local storage space
> at sk for bpf prog to use.  The space will be allocated when the first bpf
> prog has created data for this particular sk.
> 
> The design optimizes the bpf prog's lookup (and then optionally followed by
> an inline update).  bpf_spin_lock should be used if the inline update needs
> to be protected.
> 
> BPF_MAP_TYPE_SK_STORAGE:
> -----------------------
> To define a bpf "sk-local-storage", a BPF_MAP_TYPE_SK_STORAGE map (new in
> this patch) needs to be created.  Multiple BPF_MAP_TYPE_SK_STORAGE maps can
> be created to fit different bpf progs' needs.  The map enforces
> BTF to allow printing the sk-local-storage during a system-wise
> sk dump (e.g. "ss -ta") in the future.
> 
> The purpose of a BPF_MAP_TYPE_SK_STORAGE map is not for lookup/update/delete
> a "sk-local-storage" data from a particular sk.
> Think of the map as a meta-data (or "type") of a "sk-local-storage".  This
> particular "type" of "sk-local-storage" data can then be stored in any sk.
> 
> The main purposes of this map are mostly:
> 1. Define the size of a "sk-local-storage" type.
> 2. Provide a similar syscall userspace API as the map (e.g. lookup/update,
>     map-id, map-btf...etc.)
> 3. Keep track of all sk's storages of this "type" and clean them up
>     when the map is freed.
> 
> sk->sk_bpf_storage:
> ------------------
> The main lookup/update/delete is done on sk->sk_bpf_storage (which
> is a "struct bpf_sk_storage").  When doing a lookup,
> the "map" pointer is now used as the "key" to search on the
> sk_storage->list.  The "map" pointer is actually serving
> as the "type" of the "sk-local-storage" that is being
> requested.
> 
> To allow very fast lookup, it should be as fast as looking up an
> array at a stable-offset.  At the same time, it is not ideal to
> set a hard limit on the number of sk-local-storage "type" that the
> system can have.  Hence, this patch takes a cache approach.
> The last search result from sk_storage->list is cached in
> sk_storage->cache[] which is a stable sized array.  Each
> "sk-local-storage" type has a stable offset to the cache[] array.
> In the future, a map's flag could be introduced to do cache
> opt-out/enforcement if it became necessary.
> 
> All data will be removed from sk->sk_bpf_storage during
> sk destruction.
> 
> bpf_sk_storage_get() and bpf_sk_storage_delete():
> ------------------------------------------------
> Instead of using bpf_map_(lookup|update|delete)_elem(),
> the bpf prog needs to use the new helper bpf_sk_storage_get() and
> bpf_sk_storage_delete().  The verifier can then enforce the
> ARG_PTR_TO_SOCKET argument.  The bpf_sk_storage_get() also allows to
> "create" new elem if one does not exist in the sk.  It is done by
> the new BPF_SK_STORAGE_GET_F_CREATE flag.  An optional value can also be
> provided as the initial value during BPF_SK_STORAGE_GET_F_CREATE.
> The BPF_MAP_TYPE_SK_STORAGE also supports bpf_spin_lock.  Together,
> it has eliminated the potential use cases for an equivalent
> bpf_map_update_elem() API (for bpf_prog) in this patch.
> 
> Misc notes:
> ----------
> 1. map_get_next_key is not supported.  From the userspace syscall
>     perspective,  the map has the socket fd as the key while the map
>     can be shared by pinned-file or map-id.
> 
>     Since btf is enforced, the existing "ss" could be enhanced to pretty
>     print the local-storage.
> 
>     Supporting a kernel defined btf with 4 tuples as the return key could
>     be explored later also.
> 
> 2. The sk->sk_lock cannot be acquired.  Atomic operations is used instead.
>     e.g. cmpxchg is done on the sk->sk_bpf_storage ptr.
>     Please refer to the source code comments for the details in
>     synchronization cases and considerations.
> 
> 3. The mem is charged to the sk->sk_omem_alloc as the sk filter does.
> 
> Benchmark:
> ---------
> Here is the benchmark data collected by turning on
> the "kernel.bpf_stats_enabled" sysctl.
> Two bpf progs are tested:
> 
> One bpf prog with the usual bpf hashmap (max_entries = 8192) with the
> sk ptr as the key. (verifier is modified to support sk ptr as the key
> That should have shortened the key lookup time.)
> 
> Another bpf prog is with the new BPF_MAP_TYPE_SK_STORAGE.
> 
> Both are storing a "u32 cnt", do a lookup on "egress_skb/cgroup" for
> each egress skb and then bump the cnt.  netperf is used to drive
> data with 4096 connected UDP sockets.
> 
> BPF_MAP_TYPE_HASH with a modifier verifier (152ns per bpf run)
> 27: cgroup_skb  name egress_sk_map  tag 74f56e832918070b run_time_ns 58280107540 run_cnt 381347633
>      loaded_at 2019-04-15T13:46:39-0700  uid 0
>      xlated 344B  jited 258B  memlock 4096B  map_ids 16
>      btf_id 5
> 
> BPF_MAP_TYPE_SK_STORAGE in this patch (66ns per bpf run)
> 30: cgroup_skb  name egress_sk_stora  tag d4aa70984cc7bbf6 run_time_ns 25617093319 run_cnt 390989739
>      loaded_at 2019-04-15T13:47:54-0700  uid 0
>      xlated 168B  jited 156B  memlock 4096B  map_ids 17
>      btf_id 6
> 
> Here is a high-level picture on how are the objects organized:
> 
>         sk
>      +------+
>      |      |
>      |      |
>      |      |
>      |*sk_bpf_storage-----> bpf_sk_storage
>      +------+                 +-------+
>                   +-----------+ list  |
>                   |           |       |
>                   |           |       |
>                   |           |       |
>                   |           +-------+
>                   |
>                   |     elem
>                   |  +--------+
>                   +->| snode  |
>                   |  +--------+
>                   |  |  data  |          bpf_map
>                   |  +--------+        +---------+
>                   |  |map_node|<-+-----+  list   |
>                   |  +--------+  |     |         |
>                   |              |     |         |
>                   |     elem     |     |         |
>                   |  +--------+  |     +---------+
>                   +->| snode  |  |
>                      +--------+  |
>     bpf_map          |  data  |  |
>   +---------+        +--------+  |
>   |  list   +------->|map_node|  |
>   |         |        +--------+  |
>   |         |                    |
>   |         |           elem     |
>   +---------+        +--------+  |
>                   +->| snode  |  |
>                   |  +--------+  |
>                   |  |  data  |  |
>                   |  +--------+  |
>                   |  |map_node|<-+
>                   |  +--------+
>                   |
>                   |
>                   |          +-------+
>       sk          +----------| list  |
>    +------+                  |       |
>    |      |                  |       |
>    |      |                  |       |
>    |      |                  +-------+
>    |*sk_bpf_storage------->bpf_sk_storage
>    +------+
> 
> Signed-off-by: Martin KaFai Lau <kafai@...com>

Thanks. Generally look good. I have a few comments below.

> ---
>   include/linux/bpf.h          |   2 +
>   include/linux/bpf_types.h    |   1 +
>   include/net/bpf_sk_storage.h |  13 +
>   include/net/sock.h           |   5 +
>   include/uapi/linux/bpf.h     |  44 +-
>   kernel/bpf/syscall.c         |   3 +-
>   kernel/bpf/verifier.c        |  27 +-
>   net/bpf/test_run.c           |   2 +
>   net/core/Makefile            |   1 +
>   net/core/bpf_sk_storage.c    | 796 +++++++++++++++++++++++++++++++++++
>   net/core/filter.c            |  12 +
>   net/core/sock.c              |   5 +
>   12 files changed, 906 insertions(+), 5 deletions(-)
>   create mode 100644 include/net/bpf_sk_storage.h
>   create mode 100644 net/core/bpf_sk_storage.c
> 
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index f15432d90728..0d2788beacd2 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -184,6 +184,7 @@ enum bpf_arg_type {
>   	ARG_PTR_TO_MAP_KEY,	/* pointer to stack used as map key */
>   	ARG_PTR_TO_MAP_VALUE,	/* pointer to stack used as map value */
>   	ARG_PTR_TO_UNINIT_MAP_VALUE,	/* pointer to valid memory used to store a map value */
> +	ARG_PTR_TO_MAP_VALUE_OR_NULL,	/* pointer to stack used as map value or NULL */
>   
>   	/* the following constraints used to prototype bpf_memcmp() and other
>   	 * functions that access data on eBPF program stack
> @@ -204,6 +205,7 @@ enum bpf_arg_type {
>   	ARG_PTR_TO_SOCK_COMMON,	/* pointer to sock_common */
>   	ARG_PTR_TO_INT,		/* pointer to int */
>   	ARG_PTR_TO_LONG,	/* pointer to long */
> +	ARG_PTR_TO_SOCKET,	/* pointer to bpf_sock (fullsock) */
>   };
>   
>   /* type of values returned from helper functions */
> diff --git a/include/linux/bpf_types.h b/include/linux/bpf_types.h
> index d26991a16894..eb1e4f867a5e 100644
> --- a/include/linux/bpf_types.h
> +++ b/include/linux/bpf_types.h
> @@ -60,6 +60,7 @@ BPF_MAP_TYPE(BPF_MAP_TYPE_ARRAY_OF_MAPS, array_of_maps_map_ops)
>   BPF_MAP_TYPE(BPF_MAP_TYPE_HASH_OF_MAPS, htab_of_maps_map_ops)
>   #ifdef CONFIG_NET
>   BPF_MAP_TYPE(BPF_MAP_TYPE_DEVMAP, dev_map_ops)
> +BPF_MAP_TYPE(BPF_MAP_TYPE_SK_STORAGE, sk_storage_map_ops)
>   #if defined(CONFIG_BPF_STREAM_PARSER)
>   BPF_MAP_TYPE(BPF_MAP_TYPE_SOCKMAP, sock_map_ops)
>   BPF_MAP_TYPE(BPF_MAP_TYPE_SOCKHASH, sock_hash_ops)
> diff --git a/include/net/bpf_sk_storage.h b/include/net/bpf_sk_storage.h
> new file mode 100644
> index 000000000000..b9dcb02e756b
> --- /dev/null
> +++ b/include/net/bpf_sk_storage.h
> @@ -0,0 +1,13 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/* Copyright (c) 2019 Facebook */
> +#ifndef _BPF_SK_STORAGE_H
> +#define _BPF_SK_STORAGE_H
> +
> +struct sock;
> +
> +void bpf_sk_storage_free(struct sock *sk);
> +
> +extern const struct bpf_func_proto bpf_sk_storage_get_proto;
> +extern const struct bpf_func_proto bpf_sk_storage_delete_proto;
> +
> +#endif /* _BPF_SK_STORAGE_H */
[...]
> +
> +static struct bpf_sk_storage_data *
> +__sk_storage_lookup(struct bpf_sk_storage *sk_storage,
> +		    struct bpf_sk_storage_map *smap,
> +		    bool cacheit_lockit)
> +{
> +	struct bpf_sk_storage_data *sdata;
> +	struct bpf_sk_storage_elem *selem;
> +
> +	/* Fast path (cache hit) */
> +	sdata = rcu_dereference(sk_storage->cache[smap->cache_idx]);
> +	if (sdata && rcu_access_pointer(sdata->smap) == smap)
> +		return sdata;
> +
> +	/* Slow path (cache miss) */
> +	hlist_for_each_entry_rcu(selem, &sk_storage->list, snode)
> +		if (rcu_access_pointer(SDATA(selem)->smap) == smap)
> +			break;
> +
> +	if (!selem)
> +		return NULL;
> +
> +	sdata = SDATA(selem);
> +	if (cacheit_lockit) {
> +		/* spinlock is needed to avoid racing with the
> +		 * parallel delete.  Otherwise, publishing an already
> +		 * deleted sdata to the cache will become a use-after-free
> +		 * problem in the next __sk_storage_lookup().
> +		 */
> +		raw_spin_lock_bh(&sk_storage->lock);
> +		if (selem_linked_to_sk(selem))
> +			rcu_assign_pointer(sk_storage->cache[smap->cache_idx],
> +					   sdata);
> +		raw_spin_unlock_bh(&sk_storage->lock);
> +	}
> +
> +	return sdata;
> +}
> +
> +static struct bpf_sk_storage_data *
> +sk_storage_lookup(struct sock *sk, struct bpf_map *map, bool cacheit_lockit)
> +{
> +	struct bpf_sk_storage *sk_storage;
> +	struct bpf_sk_storage_map *smap;
> +
> +	sk_storage = rcu_dereference(sk->sk_bpf_storage);
> +	if (!sk_storage)
> +		return NULL;
> +
> +	smap = (struct bpf_sk_storage_map *)map;
> +	return __sk_storage_lookup(sk_storage, smap, cacheit_lockit);
> +}
> +
> +static int check_flags(const struct bpf_sk_storage_data *old_sdata,
> +		       u64 map_flags)
> +{
> +	if (old_sdata && (map_flags & ~BPF_F_LOCK) == BPF_NOEXIST)
> +		/* elem already exists */
> +		return -EEXIST;
> +
> +	if (!old_sdata && (map_flags & ~BPF_F_LOCK) == BPF_EXIST)
> +		/* elem doesn't exist, cannot update it */
> +		return -ENOENT;
> +
> +	return 0;
> +}
> +
> +static int sk_storage_alloc(struct sock *sk,
> +			    struct bpf_sk_storage_map *smap,
> +			    struct bpf_sk_storage_elem *first_selem)
> +{
> +	struct bpf_sk_storage *prev_sk_storage, *sk_storage;
> +	int err;
> +
> +	err = omem_charge(sk, sizeof(*sk_storage));
> +	if (err)
> +		return err;
> +
> +	sk_storage = kzalloc(sizeof(*sk_storage), GFP_ATOMIC | __GFP_NOWARN);
> +	if (!sk_storage) {
> +		err = -ENOMEM;
> +		goto uncharge;
> +	}
> +	INIT_HLIST_HEAD(&sk_storage->list);
> +	raw_spin_lock_init(&sk_storage->lock);
> +	sk_storage->sk = sk;
> +
> +	__selem_link_sk(sk_storage, first_selem);
> +	selem_link_map(smap, first_selem);
> +	/* Publish sk_storage to sk.  sk->sk_lock cannot be acquired.
> +	 * Hence, atomic ops is used to set sk->sk_bpf_storage
> +	 * from NULL to the newly allocated sk_storage ptr.
> +	 *
> +	 * From now on, the sk->sk_bpf_storage pointer is protected
> +	 * by the sk_storage->lock.  Hence,  when freeing
> +	 * the sk->sk_bpf_storage, the sk_storage->lock must
> +	 * be held before setting sk->sk_bpf_storage to NULL.
> +	 */
> +	prev_sk_storage = cmpxchg((struct bpf_sk_storage **)&sk->sk_bpf_storage,
> +				  NULL, sk_storage);
> +	if (unlikely(prev_sk_storage)) {
> +		selem_unlink_map(first_selem);
> +		err = -EAGAIN;
> +		goto uncharge;
> +
> +		/* Note that even first_selem was linked to smap's
> +		 * bucket->list, first_selem can be freed immediately
> +		 * (instead of kfree_rcu) because
> +		 * bpf_sk_storage_map_free() does a
> +		 * synchronize_rcu() before walking the bucket->list.
> +		 * Hence, no one is accessing selem from the
> +		 * bucket->list under rcu_read_lock().
> +		 */
> +	}
> +
> +	return 0;
> +
> +uncharge:
> +	kfree(sk_storage);
> +	atomic_sub(sizeof(*sk_storage), &sk->sk_omem_alloc);
> +	return err;
> +}
> +
> +/* sk cannot be going away because it is linking new elem
> + * to sk->sk_bpf_storage. (i.e. sk->sk_refcnt cannot be 0).
> + * Otherwise, it will become a leak (and other memory issues
> + * during map destruction).
> + */
> +static struct bpf_sk_storage_data *sk_storage_update(struct sock *sk,
> +						     struct bpf_map *map,
> +						     void *value,
> +						     u64 map_flags)
> +{
> +	struct bpf_sk_storage_data *old_sdata = NULL;
> +	struct bpf_sk_storage_elem *selem;
> +	struct bpf_sk_storage *sk_storage;
> +	struct bpf_sk_storage_map *smap;
> +	int err;
> +
> +	/* BPF_EXIST and BPF_NOEXIST cannot be both set */
> +	if (unlikely((map_flags & ~BPF_F_LOCK) > BPF_EXIST) ||
> +	    /* BPF_F_LOCK can only be used in a value with spin_lock */
> +	    unlikely((map_flags & BPF_F_LOCK) && !map_value_has_spin_lock(map)))
> +		return ERR_PTR(-EINVAL);
> +
> +	smap = (struct bpf_sk_storage_map *)map;
> +	sk_storage = rcu_dereference(sk->sk_bpf_storage);
> +	if (!sk_storage || hlist_empty(&sk_storage->list)) {

Is it possible sk_storage is not NULL and hlist_empty(&sk_storage->list) 
is true? Is this case, should we avoid allocation of new sk_storage at all?

> +		/* Very first elem for this sk */
> +		err = check_flags(NULL, map_flags);
> +		if (err)
> +			return ERR_PTR(err);
> +
> +		selem = selem_alloc(smap, sk, value, true);
> +		if (!selem)
> +			return ERR_PTR(-ENOMEM);
> +
> +		err = sk_storage_alloc(sk, smap, selem);
> +		if (err) {
> +			kfree(selem);
> +			atomic_sub(smap->elem_size, &sk->sk_omem_alloc);

discharding sk->sk_omem_alloc already happens in sk_storage_alloc?

> +			return ERR_PTR(err);
> +		}
> +
> +		return SDATA(selem);
> +	}
> +
> +	if ((map_flags & BPF_F_LOCK) && !(map_flags & BPF_NOEXIST)) {
> +		/* Hoping to find an old_sdata to do inline update
> +		 * such that it can avoid taking the sk_storage->lock
> +		 * and changing the lists.
> +		 */
> +		old_sdata = __sk_storage_lookup(sk_storage, smap, false);
> +		err = check_flags(old_sdata, map_flags);
> +		if (err)
> +			return ERR_PTR(err);
> +		if (old_sdata && selem_linked_to_sk(SELEM(old_sdata))) {
> +			copy_map_value_locked(map, old_sdata->data,
> +					      value, false);
> +			return old_sdata;
> +		}
> +	}
> +
> +	raw_spin_lock_bh(&sk_storage->lock);
> +
> +	/* Recheck sk_storage->list under sk_storage->lock */
> +	if (unlikely(hlist_empty(&sk_storage->list))) {
> +		/* A parallel del is happening and sk_storage is going
> +		 * away.  It has just been checked before, so very
> +		 * unlikely.  Return instead of retry to keep things
> +		 * simple.
> +		 */
> +		err = -EAGAIN;
> +		goto unlock_err;
> +	}
> +
> +	old_sdata = __sk_storage_lookup(sk_storage, smap, false);
> +	err = check_flags(old_sdata, map_flags);
> +	if (err)
> +		goto unlock_err;
> +
> +	if (old_sdata && (map_flags & BPF_F_LOCK)) {
> +		copy_map_value_locked(map, old_sdata->data, value, false);
> +		selem = SELEM(old_sdata);
> +		goto unlock;
> +	}
> +
> +	/* sk_storage->lock is held.  Hence, we are sure
> +	 * we can unlink and uncharge the old_sdata successfully
> +	 * later.  Hence, instead of charging the new selem now
> +	 * and then uncharge the old selem later (which may cause
> +	 * a potential but unnecessary charge failure),  avoid taking
> +	 * a charge at all here (the "!old_sdata" check) and the
> +	 * old_sdata will not be uncharged later during __selem_unlink_sk().
> +	 */
> +	selem = selem_alloc(smap, sk, value, !old_sdata);
> +	if (!selem) {
> +		err = -ENOMEM;
> +		goto unlock_err;
> +	}
> +
> +	/* First, link the new selem to the map */
> +	selem_link_map(smap, selem);
> +
> +	/* Second, link (and publish) the new selem to sk_storage */
> +	__selem_link_sk(sk_storage, selem);
> +
> +	/* Third, remove old selem, SELEM(old_sdata) */
> +	if (old_sdata) {
> +		selem_unlink_map(SELEM(old_sdata));
> +		__selem_unlink_sk(sk_storage, SELEM(old_sdata), false);
> +	}
> +
> +unlock:
> +	raw_spin_unlock_bh(&sk_storage->lock);
> +	return SDATA(selem);
> +
> +unlock_err:
> +	raw_spin_unlock_bh(&sk_storage->lock);
> +	return ERR_PTR(err);
> +}
> +
> +static int sk_storage_delete(struct sock *sk, struct bpf_map *map)
> +{
> +	struct bpf_sk_storage_data *sdata;
> +
> +	sdata = sk_storage_lookup(sk, map, false);
> +	if (!sdata)
> +		return -ENOENT;
> +
> +	selem_unlink(SELEM(sdata));
> +
> +	return 0;
> +}
> +
[...]
> +static struct bpf_map *bpf_sk_storage_map_alloc(union bpf_attr *attr)
> +{
> +	struct bpf_sk_storage_map *smap;
> +	unsigned int i;
> +	u32 nbuckets;
> +	u64 cost;
> +
> +	if (attr->map_flags != BPF_F_NO_PREALLOC || attr->max_entries ||
> +	    attr->key_size != sizeof(int) || !attr->value_size ||
> +	    /* Enforce BTF for userspace sk dumping */
> +	    !attr->btf_key_type_id || !attr->btf_value_type_id)
> +		return ERR_PTR(-EINVAL);
> +
> +	if (!capable(CAP_SYS_ADMIN))
> +		return ERR_PTR(-EPERM);
> +
> +	if (attr->value_size >= KMALLOC_MAX_SIZE -
> +	    MAX_BPF_STACK - sizeof(struct bpf_sk_storage_elem) ||
> +	    /* selem->elem_size is a u16 */
> +	    attr->value_size > U16_MAX - sizeof(struct bpf_sk_storage_elem))
> +		return ERR_PTR(-E2BIG);
> +
> +	smap = kzalloc(sizeof(*smap), GFP_USER | __GFP_NOWARN);
> +	if (!smap)
> +		return ERR_PTR(-ENOMEM);
> +	bpf_map_init_from_attr(&smap->map, attr);
> +
> +	smap->bucket_log = ilog2(roundup_pow_of_two(num_possible_cpus()));
> +	nbuckets = 1U << smap->bucket_log;
> +	smap->buckets = kvcalloc(sizeof(*smap->buckets), nbuckets,
> +				 GFP_USER | __GFP_NOWARN);
> +	if (!smap->buckets) {
> +		kfree(smap);
> +		return ERR_PTR(-ENOMEM);
> +	}
> +	cost = sizeof(*smap->buckets) * nbuckets + sizeof(*smap);
> +
> +	for (i = 0; i < nbuckets; i++) {
> +		INIT_HLIST_HEAD(&smap->buckets[i].list);
> +		raw_spin_lock_init(&smap->buckets[i].lock);
> +	}
> +
> +	smap->elem_size = sizeof(struct bpf_sk_storage_elem) + attr->value_size;
> +	smap->cache_idx = (unsigned int)atomic_inc_return(&cache_idx) %
> +		BPF_SK_STORAGE_CACHE_SIZE;
> +	smap->map.pages = round_up(cost, PAGE_SIZE) >> PAGE_SHIFT;

should we test bpf_map_precharge_memlock() here?

> +
> +	return &smap->map;
> +}
> +
> +static int notsupp_get_next_key(struct bpf_map *map, void *key,
> +				void *next_key)
> +{
> +	return -ENOTSUPP;
> +}
> +
> +static int bpf_sk_storage_map_check_btf(const struct bpf_map *map,
> +					const struct btf *btf,
> +					const struct btf_type *key_type,
> +					const struct btf_type *value_type)
> +{
> +	u32 int_data;
> +
> +	if (BTF_INFO_KIND(key_type->info) != BTF_KIND_INT)
> +		return -EINVAL;
> +
> +	int_data = *(u32 *)(key_type + 1);
> +	if (BTF_INT_BITS(int_data) != 32 || BTF_INT_OFFSET(int_data))
> +		return -EINVAL;
> +
> +	return 0;
> +}
> +
[...]> diff --git a/net/core/sock.c b/net/core/sock.c
> index 443b98d05f1e..9773be724aa9 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -137,6 +137,7 @@
>   
>   #include <linux/filter.h>
>   #include <net/sock_reuseport.h>
> +#include <net/bpf_sk_storage.h>
>   
>   #include <trace/events/sock.h>
>   
> @@ -1709,6 +1710,10 @@ static void __sk_destruct(struct rcu_head *head)
>   
>   	sock_disable_timestamp(sk, SK_FLAGS_TIMESTAMP);
>   
> +#ifdef CONFIG_BPF_SYSCALL
> +	bpf_sk_storage_free(sk);
> +#endif
> +
>   	if (atomic_read(&sk->sk_omem_alloc))
>   		pr_debug("%s: optmem leakage (%d bytes) detected\n",
>   			 __func__, atomic_read(&sk->sk_omem_alloc));
> 

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