Message-ID: <CAPhsuW6B_VJ8t8VoDhmk=H9J6PwkczscPqsB4fW_cFr1K72z6g@mail.gmail.com>
Date:   Mon, 8 Oct 2018 18:36:39 -0700
From:   Song Liu <liu.song.a23@...il.com>
To:     mauricio.vasquez@...ito.it
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Networking <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf-next 4/6] bpf: add queue and stack maps

On Mon, Oct 8, 2018 at 12:12 PM Mauricio Vasquez B
<mauricio.vasquez@...ito.it> wrote:
>
> Queue/stack maps implement a FIFO/LIFO data storage for ebpf programs.
> These maps support peek, pop and push operations that are exposed to eBPF
> programs through the new bpf_map[peek/pop/push] helpers.  Those operations
> are exposed to userspace applications through the already existing
> syscalls in the following way:
>
> BPF_MAP_LOOKUP_ELEM            -> peek
> BPF_MAP_LOOKUP_AND_DELETE_ELEM -> pop
> BPF_MAP_UPDATE_ELEM            -> push
>
> Queue/stack maps are implemented using a buffer, tail and head indexes,
> hence BPF_F_NO_PREALLOC is not supported.
>
> As opposite to other maps, queue and stack do not use RCU for protecting
> maps values, the bpf_map[peek/pop] have a ARG_PTR_TO_UNINIT_MAP_VALUE
> argument that is a pointer to a memory zone where to save the value of a
> map.  Basically the same as ARG_PTR_TO_UNINIT_MEM, but the size has not
> be passed as an extra argument.
>
> Our main motivation for implementing queue/stack maps was to keep track
> of a pool of elements, like network ports in a SNAT, however we forsee
> other use cases, like for exampling saving last N kernel events in a map
> and then analysing from userspace.
>
> Signed-off-by: Mauricio Vasquez B <mauricio.vasquez@...ito.it>
> ---
>  include/linux/bpf.h           |    7 +
>  include/linux/bpf_types.h     |    2
>  include/uapi/linux/bpf.h      |   35 ++++-
>  kernel/bpf/Makefile           |    2
>  kernel/bpf/core.c             |    3
>  kernel/bpf/helpers.c          |   43 ++++++
>  kernel/bpf/queue_stack_maps.c |  288 +++++++++++++++++++++++++++++++++++++++++
>  kernel/bpf/syscall.c          |   30 +++-
>  kernel/bpf/verifier.c         |   28 +++-
>  net/core/filter.c             |    6 +
>  10 files changed, 426 insertions(+), 18 deletions(-)
>  create mode 100644 kernel/bpf/queue_stack_maps.c
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 98c7eeb6d138..cad3bc5cffd1 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -40,6 +40,9 @@ struct bpf_map_ops {
>         int (*map_update_elem)(struct bpf_map *map, void *key, void *value, u64 flags);
>         int (*map_delete_elem)(struct bpf_map *map, void *key);
>         void *(*map_lookup_and_delete_elem)(struct bpf_map *map, void *key);
> +       int (*map_push_elem)(struct bpf_map *map, void *value, u64 flags);
> +       int (*map_pop_elem)(struct bpf_map *map, void *value);
> +       int (*map_peek_elem)(struct bpf_map *map, void *value);
>
>         /* funcs called by prog_array and perf_event_array map */
>         void *(*map_fd_get_ptr)(struct bpf_map *map, struct file *map_file,
> @@ -139,6 +142,7 @@ enum bpf_arg_type {
>         ARG_CONST_MAP_PTR,      /* const argument used as pointer to bpf_map */
>         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 */

How about we put ARG_PTR_TO_UNINIT_MAP_VALUE and related logic to a
separate patch?

>
>         /* the following constraints used to prototype bpf_memcmp() and other
>          * functions that access data on eBPF program stack
> @@ -825,6 +829,9 @@ static inline int bpf_fd_reuseport_array_update_elem(struct bpf_map *map,
>  extern const struct bpf_func_proto bpf_map_lookup_elem_proto;
>  extern const struct bpf_func_proto bpf_map_update_elem_proto;
>  extern const struct bpf_func_proto bpf_map_delete_elem_proto;
> +extern const struct bpf_func_proto bpf_map_push_elem_proto;
> +extern const struct bpf_func_proto bpf_map_pop_elem_proto;
> +extern const struct bpf_func_proto bpf_map_peek_elem_proto;
>
>  extern const struct bpf_func_proto bpf_get_prandom_u32_proto;
>  extern const struct bpf_func_proto bpf_get_smp_processor_id_proto;
> diff --git a/include/linux/bpf_types.h b/include/linux/bpf_types.h
> index 658509daacd4..a2ec73aa1ec7 100644
> --- a/include/linux/bpf_types.h
> +++ b/include/linux/bpf_types.h
> @@ -69,3 +69,5 @@ BPF_MAP_TYPE(BPF_MAP_TYPE_XSKMAP, xsk_map_ops)
>  BPF_MAP_TYPE(BPF_MAP_TYPE_REUSEPORT_SOCKARRAY, reuseport_array_ops)
>  #endif
>  #endif
> +BPF_MAP_TYPE(BPF_MAP_TYPE_QUEUE, queue_map_ops)
> +BPF_MAP_TYPE(BPF_MAP_TYPE_STACK, stack_map_ops)
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 3bb94aa2d408..bfa042273fad 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -129,6 +129,8 @@ enum bpf_map_type {
>         BPF_MAP_TYPE_CGROUP_STORAGE,
>         BPF_MAP_TYPE_REUSEPORT_SOCKARRAY,
>         BPF_MAP_TYPE_PERCPU_CGROUP_STORAGE,
> +       BPF_MAP_TYPE_QUEUE,
> +       BPF_MAP_TYPE_STACK,
>  };
>
>  enum bpf_prog_type {
> @@ -463,6 +465,28 @@ union bpf_attr {
>   *     Return
>   *             0 on success, or a negative error in case of failure.
>   *
> + * int bpf_map_push_elem(struct bpf_map *map, const void *value, u64 flags)
> + *     Description
> + *             Push an element *value* in *map*. *flags* is one of:
> + *
> + *             **BPF_EXIST**
> + *             If the queue/stack is full, the oldest element is removed to
> + *             make room for this.
> + *     Return
> + *             0 on success, or a negative error in case of failure.
> + *
> + * int bpf_map_pop_elem(struct bpf_map *map, void *value)
> + *     Description
> + *             Pop an element from *map*.
> + * Return
> + *             0 on success, or a negative error in case of failure.
> + *
> + * int bpf_map_peek_elem(struct bpf_map *map, void *value)
> + *     Description
> + *             Get an element from *map* without removing it.
> + * Return
> + *             0 on success, or a negative error in case of failure.
> + *
>   * int bpf_probe_read(void *dst, u32 size, const void *src)
>   *     Description
>   *             For tracing programs, safely attempt to read *size* bytes from
> @@ -790,14 +814,14 @@ union bpf_attr {
>   *
>   *                     int ret;
>   *                     struct bpf_tunnel_key key = {};
> - *
> + *
>   *                     ret = bpf_skb_get_tunnel_key(skb, &key, sizeof(key), 0);
>   *                     if (ret < 0)
>   *                             return TC_ACT_SHOT;     // drop packet
> - *
> + *
>   *                     if (key.remote_ipv4 != 0x0a000001)
>   *                             return TC_ACT_SHOT;     // drop packet
> - *
> + *
>   *                     return TC_ACT_OK;               // accept packet
>   *
>   *             This interface can also be used with all encapsulation devices
> @@ -2304,7 +2328,10 @@ union bpf_attr {
>         FN(skb_ancestor_cgroup_id),     \
>         FN(sk_lookup_tcp),              \
>         FN(sk_lookup_udp),              \
> -       FN(sk_release),
> +       FN(sk_release),                 \
> +       FN(map_push_elem),              \
> +       FN(map_pop_elem),               \
> +       FN(map_peek_elem),
>
>  /* integer value in 'imm' field of BPF_CALL instruction selects which helper
>   * function eBPF program intends to call
> diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
> index 0488b8258321..17afae9e65f3 100644
> --- a/kernel/bpf/Makefile
> +++ b/kernel/bpf/Makefile
> @@ -3,7 +3,7 @@ obj-y := core.o
>
>  obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o tnum.o
>  obj-$(CONFIG_BPF_SYSCALL) += hashtab.o arraymap.o percpu_freelist.o bpf_lru_list.o lpm_trie.o map_in_map.o
> -obj-$(CONFIG_BPF_SYSCALL) += local_storage.o
> +obj-$(CONFIG_BPF_SYSCALL) += local_storage.o queue_stack_maps.o
>  obj-$(CONFIG_BPF_SYSCALL) += disasm.o
>  obj-$(CONFIG_BPF_SYSCALL) += btf.o
>  ifeq ($(CONFIG_NET),y)
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index 3f5bf1af0826..8d2db076d123 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -1783,6 +1783,9 @@ BPF_CALL_0(bpf_user_rnd_u32)
>  const struct bpf_func_proto bpf_map_lookup_elem_proto __weak;
>  const struct bpf_func_proto bpf_map_update_elem_proto __weak;
>  const struct bpf_func_proto bpf_map_delete_elem_proto __weak;
> +const struct bpf_func_proto bpf_map_push_elem_proto __weak;
> +const struct bpf_func_proto bpf_map_pop_elem_proto __weak;
> +const struct bpf_func_proto bpf_map_peek_elem_proto __weak;
>
>  const struct bpf_func_proto bpf_get_prandom_u32_proto __weak;
>  const struct bpf_func_proto bpf_get_smp_processor_id_proto __weak;
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index 6502115e8f55..ab0d5e3f9892 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -76,6 +76,49 @@ const struct bpf_func_proto bpf_map_delete_elem_proto = {
>         .arg2_type      = ARG_PTR_TO_MAP_KEY,
>  };
>
> +BPF_CALL_3(bpf_map_push_elem, struct bpf_map *, map, void *, value, u64, flags)
> +{
> +       return map->ops->map_push_elem(map, value, flags);
> +}
> +
> +const struct bpf_func_proto bpf_map_push_elem_proto = {
> +       .func           = bpf_map_push_elem,
> +       .gpl_only       = false,
> +       .pkt_access     = true,
> +       .ret_type       = RET_INTEGER,
> +       .arg1_type      = ARG_CONST_MAP_PTR,
> +       .arg2_type      = ARG_PTR_TO_MAP_VALUE,
> +       .arg3_type      = ARG_ANYTHING,
> +};
> +
> +BPF_CALL_2(bpf_map_pop_elem, struct bpf_map *, map, void *, value)
> +{
> +       return map->ops->map_pop_elem(map, value);
> +}
> +
> +const struct bpf_func_proto bpf_map_pop_elem_proto = {
> +       .func           = bpf_map_pop_elem,
> +       .gpl_only       = false,
> +       .pkt_access     = true,
> +       .ret_type       = RET_INTEGER,
> +       .arg1_type      = ARG_CONST_MAP_PTR,
> +       .arg2_type      = ARG_PTR_TO_UNINIT_MAP_VALUE,
> +};
> +
> +BPF_CALL_2(bpf_map_peek_elem, struct bpf_map *, map, void *, value)
> +{
> +       return map->ops->map_peek_elem(map, value);
> +}
> +
> +const struct bpf_func_proto bpf_map_peek_elem_proto = {
> +       .func           = bpf_map_pop_elem,
> +       .gpl_only       = false,
> +       .pkt_access     = true,
> +       .ret_type       = RET_INTEGER,
> +       .arg1_type      = ARG_CONST_MAP_PTR,
> +       .arg2_type      = ARG_PTR_TO_UNINIT_MAP_VALUE,
> +};
> +
>  const struct bpf_func_proto bpf_get_prandom_u32_proto = {
>         .func           = bpf_user_rnd_u32,
>         .gpl_only       = false,
> diff --git a/kernel/bpf/queue_stack_maps.c b/kernel/bpf/queue_stack_maps.c
> new file mode 100644
> index 000000000000..12a93fb37449
> --- /dev/null
> +++ b/kernel/bpf/queue_stack_maps.c
> @@ -0,0 +1,288 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * queue_stack_maps.c: BPF queue and stack maps
> + *
> + * Copyright (c) 2018 Politecnico di Torino
> + */
> +#include <linux/bpf.h>
> +#include <linux/list.h>
> +#include <linux/slab.h>
> +#include "percpu_freelist.h"
> +
> +#define QUEUE_STACK_CREATE_FLAG_MASK \
> +       (BPF_F_NUMA_NODE | BPF_F_RDONLY | BPF_F_WRONLY)
> +
> +
> +struct bpf_queue_stack {
> +       struct bpf_map map;
> +       raw_spinlock_t lock;
> +       u32 head, tail;
> +       u32 size; /* max_entries + 1 */
> +
> +       char elements[0] __aligned(8);
> +};
> +
> +static struct bpf_queue_stack *bpf_queue_stack(struct bpf_map *map)
> +{
> +       return container_of(map, struct bpf_queue_stack, map);
> +}
> +
> +static bool queue_stack_map_is_empty(struct bpf_queue_stack *qs)
> +{
> +       return qs->head == qs->tail;
> +}
> +
> +static bool queue_stack_map_is_full(struct bpf_queue_stack *qs)
> +{
> +       u32 head = qs->head + 1;
> +
> +       if (unlikely(head >= qs->size))
> +               head = 0;
> +
> +       return head == qs->tail;
> +}
> +
> +/* Called from syscall */
> +static int queue_stack_map_alloc_check(union bpf_attr *attr)
> +{
> +       /* check sanity of attributes */
> +       if (attr->max_entries == 0 || attr->key_size != 0 ||
> +           attr->map_flags & ~QUEUE_STACK_CREATE_FLAG_MASK)
> +               return -EINVAL;
> +
> +       if (attr->value_size > KMALLOC_MAX_SIZE)
> +               /* if value_size is bigger, the user space won't be able to
> +                * access the elements.
> +                */
> +               return -E2BIG;
> +
> +       return 0;
> +}
> +
> +static struct bpf_map *queue_stack_map_alloc(union bpf_attr *attr)
> +{
> +       int ret, numa_node = bpf_map_attr_numa_node(attr);
> +       struct bpf_queue_stack *qs;
> +       u32 size, value_size;
> +       u64 queue_size, cost;
> +
> +       size = attr->max_entries + 1;
> +       value_size = attr->value_size;
> +
> +       queue_size = sizeof(*qs) + (u64) value_size * size;
> +
> +       cost = queue_size;
> +       if (cost >= U32_MAX - PAGE_SIZE)
> +               return ERR_PTR(-E2BIG);
> +
> +       cost = round_up(cost, PAGE_SIZE) >> PAGE_SHIFT;
> +
> +       ret = bpf_map_precharge_memlock(cost);
> +       if (ret < 0)
> +               return ERR_PTR(ret);
> +
> +       qs = bpf_map_area_alloc(queue_size, numa_node);
> +       if (!qs)
> +               return ERR_PTR(-ENOMEM);
> +
> +       memset(qs, 0, sizeof(*qs));
> +
> +       bpf_map_init_from_attr(&qs->map, attr);
> +
> +       qs->map.pages = cost;
> +       qs->size = size;
> +
> +       raw_spin_lock_init(&qs->lock);
> +
> +       return &qs->map;
> +}
> +
> +/* Called when map->refcnt goes to zero, either from workqueue or from syscall */
> +static void queue_stack_map_free(struct bpf_map *map)
> +{
> +       struct bpf_queue_stack *qs = bpf_queue_stack(map);
> +
> +       /* at this point bpf_prog->aux->refcnt == 0 and this map->refcnt == 0,
> +        * so the programs (can be more than one that used this map) were
> +        * disconnected from events. Wait for outstanding critical sections in
> +        * these programs to complete
> +        */
> +       synchronize_rcu();
> +
> +       bpf_map_area_free(qs);
> +}
> +
> +static int __queue_map_get(struct bpf_map *map, void *value, bool delete)
> +{
> +       struct bpf_queue_stack *qs = bpf_queue_stack(map);
> +       unsigned long flags;
> +       int err = 0;
> +       void *ptr;
> +
> +       raw_spin_lock_irqsave(&qs->lock, flags);
> +
> +       if (queue_stack_map_is_empty(qs)) {
> +               err = -ENOENT;
> +               goto out;
> +       }
> +
> +       ptr = &qs->elements[qs->tail * qs->map.value_size];
> +       memcpy(value, ptr, qs->map.value_size);
> +
> +       if (delete) {
> +               if (unlikely(++qs->tail >= qs->size))
> +                       qs->tail = 0;
> +       }
> +
> +out:
> +       raw_spin_unlock_irqrestore(&qs->lock, flags);
> +       return err;
> +}
> +
> +
> +static int __stack_map_get(struct bpf_map *map, void *value, bool delete)
> +{
> +       struct bpf_queue_stack *qs = bpf_queue_stack(map);
> +       unsigned long flags;
> +       int err = 0;
> +       void *ptr;
> +       u32 index;
> +
> +       raw_spin_lock_irqsave(&qs->lock, flags);
> +
> +       if (queue_stack_map_is_empty(qs)) {
> +               err = -ENOENT;
> +               goto out;
> +       }
> +
> +       index = qs->head - 1;
> +       if (unlikely(index >= qs->size))
> +               index = qs->size - 1;
> +
> +       ptr = &qs->elements[index * qs->map.value_size];
> +       memcpy(value, ptr, qs->map.value_size);
> +
> +       if (delete)
> +               qs->head = index;
> +
> +out:
> +       raw_spin_unlock_irqrestore(&qs->lock, flags);
> +       return err;
> +}
> +
> +/* Called from syscall or from eBPF program */
> +static int queue_map_peek_elem(struct bpf_map *map, void *value)
> +{
> +       return __queue_map_get(map, value, false);
> +}
> +
> +/* Called from syscall or from eBPF program */
> +static int stack_map_peek_elem(struct bpf_map *map, void *value)
> +{
> +       return __stack_map_get(map, value, false);
> +}
> +
> +/* Called from syscall or from eBPF program */
> +static int queue_map_pop_elem(struct bpf_map *map, void *value)
> +{
> +       return __queue_map_get(map, value, true);
> +}
> +
> +/* Called from syscall or from eBPF program */
> +static int stack_map_pop_elem(struct bpf_map *map, void *value)
> +{
> +       return __stack_map_get(map, value, true);
> +}
> +
> +/* Called from syscall or from eBPF program */
> +static int queue_stack_map_push_elem(struct bpf_map *map, void *value,
> +                                    u64 flags)
> +{
> +       struct bpf_queue_stack *qs = bpf_queue_stack(map);
> +       unsigned long irq_flags;
> +       int err = 0;
> +       void *dst;
> +
> +       /* BPF_EXIST is used to force making room for a new element in case the
> +        * map is full
> +        */
> +       bool replace = (flags & BPF_EXIST);
> +
> +       /* Check supported flags for queue and stack maps */
> +       if (flags & BPF_NOEXIST || flags > BPF_EXIST)
> +               return -EINVAL;
> +
> +       raw_spin_lock_irqsave(&qs->lock, irq_flags);
> +
> +       if (queue_stack_map_is_full(qs)) {
> +               if (!replace) {
> +                       err = -E2BIG;
> +                       goto out;
> +               }
> +               /* advance tail pointer to overwrite oldest element */
> +               if (unlikely(++qs->tail >= qs->size))
> +                       qs->tail = 0;
> +       }
> +
> +       dst = &qs->elements[qs->head * qs->map.value_size];
> +       memcpy(dst, value, qs->map.value_size);
> +
> +       if (unlikely(++qs->head >= qs->size))
> +               qs->head = 0;
> +
> +out:
> +       raw_spin_unlock_irqrestore(&qs->lock, irq_flags);
> +       return err;
> +}
> +
> +/* Called from syscall or from eBPF program */
> +static void *queue_stack_map_lookup_elem(struct bpf_map *map, void *key)
> +{
> +       return NULL;
> +}
> +
> +/* Called from syscall or from eBPF program */
> +static int queue_stack_map_update_elem(struct bpf_map *map, void *key,
> +                                      void *value, u64 flags)
> +{
> +       return -EINVAL;
> +}
> +
> +/* Called from syscall or from eBPF program */
> +static int queue_stack_map_delete_elem(struct bpf_map *map, void *key)
> +{
> +       return -EINVAL;
> +}
> +
> +/* Called from syscall */
> +static int queue_stack_map_get_next_key(struct bpf_map *map, void *key,
> +                                       void *next_key)
> +{
> +       return -EINVAL;
> +}
> +
> +const struct bpf_map_ops queue_map_ops = {
> +       .map_alloc_check = queue_stack_map_alloc_check,
> +       .map_alloc = queue_stack_map_alloc,
> +       .map_free = queue_stack_map_free,
> +       .map_lookup_elem = queue_stack_map_lookup_elem,
> +       .map_update_elem = queue_stack_map_update_elem,
> +       .map_delete_elem = queue_stack_map_delete_elem,
> +       .map_push_elem = queue_stack_map_push_elem,
> +       .map_pop_elem = queue_map_pop_elem,
> +       .map_peek_elem = queue_map_peek_elem,
> +       .map_get_next_key = queue_stack_map_get_next_key,
> +};
> +
> +const struct bpf_map_ops stack_map_ops = {
> +       .map_alloc_check = queue_stack_map_alloc_check,
> +       .map_alloc = queue_stack_map_alloc,
> +       .map_free = queue_stack_map_free,
> +       .map_lookup_elem = queue_stack_map_lookup_elem,
> +       .map_update_elem = queue_stack_map_update_elem,
> +       .map_delete_elem = queue_stack_map_delete_elem,
> +       .map_push_elem = queue_stack_map_push_elem,
> +       .map_pop_elem = stack_map_pop_elem,
> +       .map_peek_elem = stack_map_peek_elem,
> +       .map_get_next_key = queue_stack_map_get_next_key,
> +};
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index c33d9303f72f..c135d205fd09 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -727,6 +727,9 @@ static int map_lookup_elem(union bpf_attr *attr)
>                 err = bpf_fd_htab_map_lookup_elem(map, key, value);
>         } else if (map->map_type == BPF_MAP_TYPE_REUSEPORT_SOCKARRAY) {
>                 err = bpf_fd_reuseport_array_lookup_elem(map, key, value);
> +       } else if (map->map_type == BPF_MAP_TYPE_QUEUE ||
> +                  map->map_type == BPF_MAP_TYPE_STACK) {
> +               err = map->ops->map_peek_elem(map, value);
>         } else {
>                 rcu_read_lock();
>                 ptr = map->ops->map_lookup_elem(map, key);
> @@ -841,6 +844,9 @@ static int map_update_elem(union bpf_attr *attr)
>                 /* rcu_read_lock() is not needed */
>                 err = bpf_fd_reuseport_array_update_elem(map, key, value,
>                                                          attr->flags);
> +       } else if (map->map_type == BPF_MAP_TYPE_QUEUE ||
> +                  map->map_type == BPF_MAP_TYPE_STACK) {
> +               err = map->ops->map_push_elem(map, value, attr->flags);
>         } else {
>                 rcu_read_lock();
>                 err = map->ops->map_update_elem(map, key, value, attr->flags);
> @@ -1023,16 +1029,22 @@ static int map_lookup_and_delete_elem(union bpf_attr *attr)
>          */
>         preempt_disable();
>         __this_cpu_inc(bpf_prog_active);
> -       if (!map->ops->map_lookup_and_delete_elem) {
> -               err = -ENOTSUPP;
> -               goto free_value;
> +       if (map->map_type == BPF_MAP_TYPE_QUEUE ||
> +           map->map_type == BPF_MAP_TYPE_STACK) {
> +               err = map->ops->map_pop_elem(map, value);
> +       } else {
> +               if (!map->ops->map_lookup_and_delete_elem) {
> +                       err = -ENOTSUPP;
> +                       goto free_value;

similar to previous patch: either we move this check, or we add
__this_cpu_dec() and preempt_enable().

Thanks,
Song

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