Commit fb5b4802 authored by Martin KaFai Lau's avatar Martin KaFai Lau Committed by Alexei Starovoitov
Browse files

bpf: Add bpf_list_{front,back} kfunc 



In the kernel fq qdisc implementation, it only needs to look at
the fields of the first node in a list but does not always
need to remove it from the list. It is more convenient to have
a peek kfunc for the list. It works similar to the bpf_rbtree_first().

This patch adds bpf_list_{front,back} kfunc. The verifier is changed
such that the kfunc returning "struct bpf_list_node *" will be
marked as non-owning. The exception is the KF_ACQUIRE kfunc. The
net effect is only the new bpf_list_{front,back} kfuncs will
have its return pointer marked as non-owning.

Acked-by: default avatarKumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: default avatarMartin KaFai Lau <martin.lau@kernel.org>
Link: https://lore.kernel.org/r/20250506015857.817950-8-martin.lau@linux.dev


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 3fab84f0

kernel/bpf/helpers.c

+22 −0
Original line number Diff line number Diff line
@@ -2293,6 +2293,26 @@ __bpf_kfunc struct bpf_list_node *bpf_list_pop_back(struct bpf_list_head *head) 
	return __bpf_list_del(head, true);

}



__bpf_kfunc struct bpf_list_node *bpf_list_front(struct bpf_list_head *head)

{

	struct list_head *h = (struct list_head *)head;



	if (list_empty(h) || unlikely(!h->next))

		return NULL;



	return (struct bpf_list_node *)h->next;

}



__bpf_kfunc struct bpf_list_node *bpf_list_back(struct bpf_list_head *head)

{

	struct list_head *h = (struct list_head *)head;



	if (list_empty(h) || unlikely(!h->next))

		return NULL;



	return (struct bpf_list_node *)h->prev;

}



__bpf_kfunc struct bpf_rb_node *bpf_rbtree_remove(struct bpf_rb_root *root,

						  struct bpf_rb_node *node)

{
@@ -3236,6 +3256,8 @@ BTF_ID_FLAGS(func, bpf_list_push_front_impl) 
BTF_ID_FLAGS(func, bpf_list_push_back_impl)

BTF_ID_FLAGS(func, bpf_list_pop_front, KF_ACQUIRE | KF_RET_NULL)

BTF_ID_FLAGS(func, bpf_list_pop_back, KF_ACQUIRE | KF_RET_NULL)

BTF_ID_FLAGS(func, bpf_list_front, KF_RET_NULL)

BTF_ID_FLAGS(func, bpf_list_back, KF_RET_NULL)

BTF_ID_FLAGS(func, bpf_task_acquire, KF_ACQUIRE | KF_RCU | KF_RET_NULL)

BTF_ID_FLAGS(func, bpf_task_release, KF_RELEASE)

BTF_ID_FLAGS(func, bpf_rbtree_remove, KF_ACQUIRE | KF_RET_NULL)

kernel/bpf/verifier.c

+10 −2
Original line number Diff line number Diff line
@@ -12079,6 +12079,8 @@ enum special_kfunc_type { 
	KF_bpf_list_push_back_impl,

	KF_bpf_list_pop_front,

	KF_bpf_list_pop_back,

	KF_bpf_list_front,

	KF_bpf_list_back,

	KF_bpf_cast_to_kern_ctx,

	KF_bpf_rdonly_cast,

	KF_bpf_rcu_read_lock,
@@ -12124,6 +12126,8 @@ BTF_ID(func, bpf_list_push_front_impl) 
BTF_ID(func, bpf_list_push_back_impl)

BTF_ID(func, bpf_list_pop_front)

BTF_ID(func, bpf_list_pop_back)

BTF_ID(func, bpf_list_front)

BTF_ID(func, bpf_list_back)

BTF_ID(func, bpf_cast_to_kern_ctx)

BTF_ID(func, bpf_rdonly_cast)

BTF_ID(func, bpf_rbtree_remove)
@@ -12160,6 +12164,8 @@ BTF_ID(func, bpf_list_push_front_impl) 
BTF_ID(func, bpf_list_push_back_impl)

BTF_ID(func, bpf_list_pop_front)

BTF_ID(func, bpf_list_pop_back)

BTF_ID(func, bpf_list_front)

BTF_ID(func, bpf_list_back)

BTF_ID(func, bpf_cast_to_kern_ctx)

BTF_ID(func, bpf_rdonly_cast)

BTF_ID(func, bpf_rcu_read_lock)
@@ -12598,7 +12604,9 @@ static bool is_bpf_list_api_kfunc(u32 btf_id) 
	return btf_id == special_kfunc_list[KF_bpf_list_push_front_impl] ||

	       btf_id == special_kfunc_list[KF_bpf_list_push_back_impl] ||

	       btf_id == special_kfunc_list[KF_bpf_list_pop_front] ||

	       btf_id == special_kfunc_list[KF_bpf_list_pop_back];

	       btf_id == special_kfunc_list[KF_bpf_list_pop_back] ||

	       btf_id == special_kfunc_list[KF_bpf_list_front] ||

	       btf_id == special_kfunc_list[KF_bpf_list_back];

}









static bool is_bpf_rbtree_api_kfunc(u32 btf_id)








@@ -13903,7 +13911,7 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,







			if (is_kfunc_ret_null(&meta))









				regs[BPF_REG_0].id = id;









			regs[BPF_REG_0].ref_obj_id = id;









		} else if (is_rbtree_node_type(ptr_type)) {









		} else if (is_rbtree_node_type(ptr_type) || is_list_node_type(ptr_type)) {









			ref_set_non_owning(env, &regs[BPF_REG_0]);









		}