linux-kernel - Re: [PATCH] bpf/verifier: allow calling bpf_kptr

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Message-ID: <CAADnVQ+TwUwzrWZ3EJnPz4S48HqBJxw3+OA6UL-K4CWgU+4PvA@mail.gmail.com>
Date: Thu, 22 Jan 2026 19:34:39 -0800
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: chengkaitao <pilgrimtao@...il.com>
Cc: Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	John Fastabend <john.fastabend@...il.com>, Andrii Nakryiko <andrii@...nel.org>, 
	Martin KaFai Lau <martin.lau@...ux.dev>, Eduard <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, KP Singh <kpsingh@...nel.org>, 
	Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, 
	bpf <bpf@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, 
	Chengkaitao <chengkaitao@...inos.cn>
Subject: Re: [PATCH] bpf/verifier: allow calling bpf_kptr_xchg while holding a lock

On Thu, Jan 22, 2026 at 12:14 AM chengkaitao <pilgrimtao@...il.com> wrote:
>
> From: Chengkaitao <chengkaitao@...inos.cn>
>
> For the following scenario:
> struct tree_node {
>     struct bpf_rb_node node;
>     struct request __kptr *req;
>     u64 key;
> };
> struct bpf_rb_root tree_root __contains(tree_node, node);
> struct bpf_spin_lock tree_lock;
>
> If we need to traverse all nodes in the rbtree, retrieve the __kptr
> pointer from each node, and read kernel data from the referenced
> object, using bpf_kptr_xchg appears unavoidable.
>
> This patch skips the BPF verifier checks for bpf_kptr_xchg when
> called while holding a lock.
>
> Signed-off-by: Chengkaitao <chengkaitao@...inos.cn>

The idea of the patch makes sense, but selftests is required
and you have to use proper full name in SOB.

pw-bot: cr