Re: [PATCH net v4] bpf, net: Check cgroup_bpf_enabled() only once in do_sock_getsockopt()
From: Alexei Starovoitov <hidden>
Date: 2024-08-22 16:00:48
Also in:
bpf, linux-arm-kernel, linux-mediatek, lkml
On Thu, Aug 22, 2024 at 12:02 AM Tze-nan Wu (吳澤南) [off-list ref] wrote:
quoted hunk ↗ jump to hunk
BTW, If this should be handled in kernel, modification shown below could fix the issue without breaking the "static_branch" usage in both macros:+++ /include/linux/bpf-cgroup.h: -#define BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen) +#define BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen, compat) ({ int __ret = 0; if (cgroup_bpf_enabled(CGROUP_GETSOCKOPT)) copy_from_sockptr(&__ret, optlen, sizeof(int)); + else + *compat = true; __ret; }) #define BPF_CGROUP_RUN_PROG_GETSOCKOPT(sock, level, optname,optval, optlen, max_optlen, retval) ({ int __ret = retval; - if (cgroup_bpf_enabled(CGROUP_GETSOCKOPT) && - cgroup_bpf_sock_enabled(sock, CGROUP_GETSOCKOPT)) + if (cgroup_bpf_sock_enabled(sock, CGROUP_GETSOCKOPT)) if (!(sock)->sk_prot->bpf_bypass_getsockopt || ... +++ /net/socket.c: int do_sock_getsockopt(struct socket *sock, bool compat, int level, { ... ... + /* The meaning of `compat` variable could be changed here + * to indicate if cgroup_bpf_enabled(CGROUP_SOCK_OPS) is false. + */ if (!compat) - max_optlen = BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen); + max_optlen = BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen, &compat);
This is better, but it's still quite a hack. Let's not override it. We can have another bool, but the question: do we really need BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN ? copy_from_sockptr(&__ret, optlen, sizeof(int)); should be fast enough to do it unconditionally. What are we saving here? Stan ?
quoted
Thanks, --tze-nan*********** MEDIATEK Confidentiality Notice ***********
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