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Message-Id: <Yl2W5ThWCFPIeLW8@google.com> Date: Mon, 18 Apr 2022 09:50:45 -0700 From: sdf@...gle.com To: Alexei Starovoitov <alexei.starovoitov@...il.com> Cc: Network Development <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <kafai@...com> Subject: Re: [PATCH bpf-next v2] bpf: move rcu lock management out of BPF_PROG_RUN routines On 04/16, Alexei Starovoitov wrote: > On Thu, Apr 14, 2022 at 9:12 AM Stanislav Fomichev <sdf@...gle.com> wrote: > > +static int > > +bpf_prog_run_array_cg_flags(const struct cgroup_bpf *cgrp, > > + enum cgroup_bpf_attach_type atype, > > + const void *ctx, bpf_prog_run_fn run_prog, > > + int retval, u32 *ret_flags) > > +{ > > + const struct bpf_prog_array_item *item; > > + const struct bpf_prog *prog; > > + const struct bpf_prog_array *array; > > + struct bpf_run_ctx *old_run_ctx; > > + struct bpf_cg_run_ctx run_ctx; > > + u32 func_ret; > > + > > + run_ctx.retval = retval; > > + migrate_disable(); > > + rcu_read_lock(); > > + array = rcu_dereference(cgrp->effective[atype]); > > + item = &array->items[0]; > > + old_run_ctx = bpf_set_run_ctx(&run_ctx.run_ctx); > > + while ((prog = READ_ONCE(item->prog))) { > > + run_ctx.prog_item = item; > > + func_ret = run_prog(prog, ctx); > ... > > + ret = bpf_prog_run_array_cg(&cgrp->bpf, CGROUP_GETSOCKOPT, > > &ctx, bpf_prog_run, retval); > Did you check the asm that bpf_prog_run gets inlined > after being passed as a pointer to a function? > Crossing fingers... I suspect not every compiler can do that :( > De-virtualization optimization used to be tricky. No, I didn't, but looking at it right now, both gcc and clang seem to be doing inlining all way up to bpf_dispatcher_nop_func. clang: 0000000000001750 <__cgroup_bpf_run_filter_sock_addr>: __cgroup_bpf_run_filter_sock_addr(): ./kernel/bpf/cgroup.c:1226 int __cgroup_bpf_run_filter_sock_addr(struct sock *sk, struct sockaddr *uaddr, enum cgroup_bpf_attach_type atype, void *t_ctx, u32 *flags) { ... ./include/linux/filter.h:628 ret = dfunc(ctx, prog->insnsi, prog->bpf_func); 1980: 49 8d 75 48 lea 0x48(%r13),%rsi bpf_dispatcher_nop_func(): ./include/linux/bpf.h:804 return bpf_func(ctx, insnsi); 1984: 4c 89 f7 mov %r14,%rdi 1987: 41 ff 55 30 call *0x30(%r13) 198b: 89 c3 mov %eax,%ebx gcc (w/retpoline): 0000000000001110 <__cgroup_bpf_run_filter_sock_addr>: __cgroup_bpf_run_filter_sock_addr(): kernel/bpf/cgroup.c:1226 { ... ./include/linux/filter.h:628 ret = dfunc(ctx, prog->insnsi, prog->bpf_func); 11c5: 49 8d 75 48 lea 0x48(%r13),%rsi bpf_dispatcher_nop_func(): ./include/linux/bpf.h:804 11c9: 48 8d 7c 24 10 lea 0x10(%rsp),%rdi 11ce: e8 00 00 00 00 call 11d3 <__cgroup_bpf_run_filter_sock_addr+0xc3> 11cf: R_X86_64_PLT32 __x86_indirect_thunk_rax-0x4 11d3: 89 c3 mov %eax,%ebx
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