From: Kui-Feng Lee <sinquersw@gmail.com>
To: Martin KaFai Lau <martin.lau@linux.dev>, Kui-Feng Lee <kuifeng@meta.com>
Cc: bpf@vger.kernel.org, ast@kernel.org, song@kernel.org,
kernel-team@meta.com, andrii@kernel.org
Subject: Re: [PATCH bpf-next 3/7] bpf: Register and unregister a struct_ops by their bpf_links.
Date: Thu, 16 Feb 2023 08:42:04 -0800 [thread overview]
Message-ID: <28a01a8a-77d2-dcdc-eda4-a6ff7c7b54c0@gmail.com> (raw)
In-Reply-To: <4f5012d6-e07a-2602-3526-d43244d9d978@linux.dev>
On 2/15/23 16:37, Martin KaFai Lau wrote:
> On 2/14/23 2:17 PM, Kui-Feng Lee wrote:
>> Registration via bpf_links ensures a uniform behavior, just like other
>> BPF programs. BPF struct_ops were registered/unregistered when
>> updating/deleting their values. Only the maps of struct_ops having
>> the BPF_F_LINK flag are allowed to back a bpf_link.
>>
>> Signed-off-by: Kui-Feng Lee <kuifeng@meta.com>
>> ---
>> include/uapi/linux/bpf.h | 3 ++
>> kernel/bpf/bpf_struct_ops.c | 59 +++++++++++++++++++++++++++++++---
>> tools/include/uapi/linux/bpf.h | 3 ++
>> 3 files changed, 61 insertions(+), 4 deletions(-)
>>
>> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
>> index 1e6cdd0f355d..48d8b3058aa1 100644
>> --- a/include/uapi/linux/bpf.h
>> +++ b/include/uapi/linux/bpf.h
>> @@ -1267,6 +1267,9 @@ enum {
>> /* Create a map that is suitable to be an inner map with dynamic max
>> entries */
>> BPF_F_INNER_MAP = (1U << 12),
>> +
>> +/* Create a map that will be registered/unregesitered by the backed
>> bpf_link */
>> + BPF_F_LINK = (1U << 13),
>> };
>> /* Flags for BPF_PROG_QUERY. */
>> diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
>> index 621c8e24481a..d16ca06cf09a 100644
>> --- a/kernel/bpf/bpf_struct_ops.c
>> +++ b/kernel/bpf/bpf_struct_ops.c
>> @@ -390,7 +390,7 @@ static int bpf_struct_ops_map_update_elem(struct
>> bpf_map *map, void *key,
>> mutex_lock(&st_map->lock);
>> - if (kvalue->state != BPF_STRUCT_OPS_STATE_INIT) {
>> + if (kvalue->state != BPF_STRUCT_OPS_STATE_INIT ||
>> refcount_read(&kvalue->refcnt)) {
>
> Why it needs a new refcount_read(&kvalue->refcnt) check?
It prohibits updating the value once it is registered.
This refcnt is set to 1 when register it.
But, yes, it is confusing since we never reset it back to *_INIT.
The purpose of this refcount_read() will be clear once add *_UNREG, and
reset it back to *_INIT properly.
>
>> err = -EBUSY;
>> goto unlock;
>> }
>> @@ -491,6 +491,12 @@ static int bpf_struct_ops_map_update_elem(struct
>> bpf_map *map, void *key,
>> *(unsigned long *)(udata + moff) = prog->aux->id;
>> }
>> + if (st_map->map.map_flags & BPF_F_LINK) {
>> + /* Let bpf_link handle registration & unregistration. */
>> + smp_store_release(&kvalue->state, BPF_STRUCT_OPS_STATE_INUSE);
>
> INUSE is for registered struct_ops. It needs a new UNREG state to mean
> initialized but not registered. The kvalue->state is not in uapi but the
> user space can still introspect it (thanks to BTF), so having a correct
> semantic state is useful. Try 'bpftool struct_ops dump ...':
>
> "bpf_struct_ops_tcp_congestion_ops": {
> "refcnt": {
> "refs": {
> "counter": 1
> }
> },
> "state": "BPF_STRUCT_OPS_STATE_INUSE",
Ok! That make sense.
>
>> + goto unlock;
>> + }
>> +
>> refcount_set(&kvalue->refcnt, 1);
>> bpf_map_inc(map);
>> @@ -522,6 +528,7 @@ static int bpf_struct_ops_map_update_elem(struct
>> bpf_map *map, void *key,
>> kfree(tlinks);
>> mutex_unlock(&st_map->lock);
>> return err;
>> +
>
> Unnecessary new line.
>
>> }
>> static int bpf_struct_ops_map_delete_elem(struct bpf_map *map, void
>> *key)
>> @@ -535,6 +542,8 @@ static int bpf_struct_ops_map_delete_elem(struct
>> bpf_map *map, void *key)
>> BPF_STRUCT_OPS_STATE_TOBEFREE);
>> switch (prev_state) {
>> case BPF_STRUCT_OPS_STATE_INUSE:
>> + if (st_map->map.map_flags & BPF_F_LINK)
>> + return 0;
>
> This should be a -ENOTSUPP.
Sure!
>
>> st_map->st_ops->unreg(&st_map->kvalue.data);
>> if (refcount_dec_and_test(&st_map->kvalue.refcnt))
>> bpf_map_put(map);
>> @@ -585,7 +594,7 @@ static void bpf_struct_ops_map_free(struct bpf_map
>> *map)
>> static int bpf_struct_ops_map_alloc_check(union bpf_attr *attr)
>> {
>> if (attr->key_size != sizeof(unsigned int) || attr->max_entries
>> != 1 ||
>> - attr->map_flags || !attr->btf_vmlinux_value_type_id)
>> + (attr->map_flags & ~BPF_F_LINK) ||
>> !attr->btf_vmlinux_value_type_id)
>> return -EINVAL;
>> return 0;
>> }
>> @@ -638,6 +647,8 @@ static struct bpf_map
>> *bpf_struct_ops_map_alloc(union bpf_attr *attr)
>> set_vm_flush_reset_perms(st_map->image);
>> bpf_map_init_from_attr(map, attr);
>> + map->map_flags |= attr->map_flags & BPF_F_LINK;
>
> This should have already been done in bpf_map_init_from_attr().
bpf_map_init_from_attr() will filter out all flags except BPF_F_RDONLY &
BPF_F_WRONLY. But, I can move it to bpf_map_init_from_attr() by not
filtering out it.
>
>> +
>> return map;
>> }
>> @@ -699,10 +710,25 @@ void bpf_struct_ops_put(const void *kdata)
>> }
>> }
>> +static void bpf_struct_ops_kvalue_put(struct bpf_struct_ops_value
>> *kvalue)
>> +{
>> + struct bpf_struct_ops_map *st_map;
>> +
>> + if (refcount_dec_and_test(&kvalue->refcnt)) {
>> + st_map = container_of(kvalue, struct bpf_struct_ops_map,
>> + kvalue);
>> + bpf_map_put(&st_map->map);
>> + }
>> +}
>> +
>> static void bpf_struct_ops_map_link_release(struct bpf_link *link)
>> {
>> + struct bpf_struct_ops_map *st_map;
>> +
>> if (link->map) {
>> - bpf_map_put(link->map);
>> + st_map = (struct bpf_struct_ops_map *)link->map;
>> + st_map->st_ops->unreg(&st_map->kvalue.data);
>> + bpf_struct_ops_kvalue_put(&st_map->kvalue);
>> link->map = NULL;
>
> Does it need a lock or something to protect the link_release? or I am
> missing something and lock is not needed?
This function will be called by bpf_link_free() following the pointer in
bpf_link_ops. And bpf_link_free() is called by bpf_link_put(). The
refcnt of bpf_link is maintained by bpf_link_put(), and the function
here indirectly only if the refcnt reachs 0. If I don't miss anything,
it should be safe to release a link without a lock.
>
> The kvalue->value state should become UNREG.
>
> After UNREG, can the struct_ops map be used in creating a new link again?
>
It should be.
>> }
>> }
>> @@ -735,13 +761,15 @@ static const struct bpf_link_ops
>> bpf_struct_ops_map_lops = {
>> int link_create_struct_ops_map(union bpf_attr *attr, bpfptr_t uattr)
>> {
>> + struct bpf_struct_ops_map *st_map;
>> struct bpf_link_primer link_primer;
>> + struct bpf_struct_ops_value *kvalue;
>> struct bpf_map *map;
>> struct bpf_link *link = NULL;
>> int err;
>> map = bpf_map_get(attr->link_create.prog_fd);
>> - if (map->map_type != BPF_MAP_TYPE_STRUCT_OPS)
>> + if (map->map_type != BPF_MAP_TYPE_STRUCT_OPS || !(map->map_flags
>> & BPF_F_LINK))
>> return -EINVAL;
>> link = kzalloc(sizeof(*link), GFP_USER);
>> @@ -752,6 +780,29 @@ int link_create_struct_ops_map(union bpf_attr
>> *attr, bpfptr_t uattr)
>> bpf_link_init(link, BPF_LINK_TYPE_STRUCT_OPS,
>> &bpf_struct_ops_map_lops, NULL);
>> link->map = map;
>> + if (map->map_flags & BPF_F_LINK) {
>> + st_map = (struct bpf_struct_ops_map *)map;
>> + kvalue = (struct bpf_struct_ops_value *)&st_map->kvalue;
>> +
>> + if (kvalue->state != BPF_STRUCT_OPS_STATE_INUSE ||
>> + refcount_read(&kvalue->refcnt) != 0) {
>
> The refcount_read(&kvalue->refcnt) is to ensure it is not registered?
> It seems the UNREG state is useful here.
Yes!
>
>> + err = -EINVAL;
>> + goto err_out;
>> + }
>> +
>> + refcount_set(&kvalue->refcnt, 1);
>
> If a struct_ops map is used to create multiple links in parallel, is it
> safe?
>
>> +
>> + set_memory_rox((long)st_map->image, 1);
>> + err = st_map->st_ops->reg(kvalue->data);
>
> After successful reg, the state can be changed from UNREG to INUSE.
>
>> + if (err) {
>> + refcount_set(&kvalue->refcnt, 0);
>> +
>> + set_memory_nx((long)st_map->image, 1);
>> + set_memory_rw((long)st_map->image, 1);
>> + goto err_out;
>> + }
>> + }
>
> This patch should be combined with patch 1. Otherwise, patch 1 is quite
> hard to understand without link_create_struct_ops_map() doing the actual
> "attach".
Ok!
>
>> +
>> err = bpf_link_prime(link, &link_primer);
>> if (err)
>> goto err_out;
>> diff --git a/tools/include/uapi/linux/bpf.h
>> b/tools/include/uapi/linux/bpf.h
>> index 1e6cdd0f355d..48d8b3058aa1 100644
>> --- a/tools/include/uapi/linux/bpf.h
>> +++ b/tools/include/uapi/linux/bpf.h
>> @@ -1267,6 +1267,9 @@ enum {
>> /* Create a map that is suitable to be an inner map with dynamic max
>> entries */
>> BPF_F_INNER_MAP = (1U << 12),
>> +
>> +/* Create a map that will be registered/unregesitered by the backed
>> bpf_link */
>> + BPF_F_LINK = (1U << 13),
>> };
>> /* Flags for BPF_PROG_QUERY. */
>
next prev parent reply other threads:[~2023-02-16 16:42 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-14 22:17 [PATCH bpf-next 0/7] Transit between BPF TCP congestion controls Kui-Feng Lee
2023-02-14 22:17 ` [PATCH bpf-next 1/7] bpf: Create links for BPF struct_ops maps Kui-Feng Lee
2023-02-15 0:26 ` kernel test robot
2023-02-15 2:39 ` Stanislav Fomichev
2023-02-15 18:04 ` Kui-Feng Lee
2023-02-15 18:44 ` Stanislav Fomichev
2023-02-15 20:24 ` Kui-Feng Lee
2023-02-15 21:28 ` Martin KaFai Lau
2023-02-15 20:30 ` Martin KaFai Lau
2023-02-15 20:55 ` Kui-Feng Lee
2023-02-15 22:58 ` Martin KaFai Lau
2023-02-16 17:59 ` Kui-Feng Lee
2023-02-14 22:17 ` [PATCH bpf-next 2/7] net: Update an existing TCP congestion control algorithm Kui-Feng Lee
2023-02-15 2:43 ` Stanislav Fomichev
2023-02-15 18:15 ` Kui-Feng Lee
2023-02-14 22:17 ` [PATCH bpf-next 3/7] bpf: Register and unregister a struct_ops by their bpf_links Kui-Feng Lee
2023-02-15 2:53 ` Stanislav Fomichev
2023-02-15 18:29 ` Kui-Feng Lee
2023-02-16 0:37 ` Martin KaFai Lau
2023-02-16 16:42 ` Kui-Feng Lee [this message]
2023-02-16 22:38 ` Martin KaFai Lau
2023-02-17 22:17 ` Kui-Feng Lee
2023-02-14 22:17 ` [PATCH bpf-next 4/7] libbpf: Create a bpf_link in bpf_map__attach_struct_ops() Kui-Feng Lee
2023-02-15 2:58 ` Stanislav Fomichev
2023-02-15 18:44 ` Kui-Feng Lee
2023-02-15 18:48 ` Stanislav Fomichev
2023-02-15 22:20 ` Kui-Feng Lee
2023-02-16 22:40 ` Andrii Nakryiko
2023-02-16 22:59 ` Martin KaFai Lau
2023-02-18 0:05 ` Kui-Feng Lee
2023-02-18 1:08 ` Andrii Nakryiko
2023-02-14 22:17 ` [PATCH bpf-next 5/7] bpf: Update the struct_ops of a bpf_link Kui-Feng Lee
2023-02-16 1:02 ` Martin KaFai Lau
2023-02-16 19:17 ` Kui-Feng Lee
2023-02-16 19:40 ` Martin KaFai Lau
2023-02-14 22:17 ` [PATCH bpf-next 6/7] libbpf: Update a bpf_link with another struct_ops Kui-Feng Lee
2023-02-16 22:48 ` Andrii Nakryiko
2023-02-18 0:22 ` Kui-Feng Lee
2023-02-18 1:10 ` Andrii Nakryiko
2023-02-21 22:20 ` Kui-Feng Lee
2023-02-14 22:17 ` [PATCH bpf-next 7/7] selftests/bpf: Test switching TCP Congestion Control algorithms Kui-Feng Lee
2023-02-16 22:50 ` Andrii Nakryiko
2023-02-18 0:23 ` Kui-Feng Lee
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