From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 03F9DC433F5 for ; Tue, 19 Apr 2022 15:42:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1353979AbiDSPpJ (ORCPT ); Tue, 19 Apr 2022 11:45:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47152 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240723AbiDSPpI (ORCPT ); Tue, 19 Apr 2022 11:45:08 -0400 Received: from mail-yb1-xb4a.google.com (mail-yb1-xb4a.google.com [IPv6:2607:f8b0:4864:20::b4a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3167A17E36 for ; Tue, 19 Apr 2022 08:42:25 -0700 (PDT) Received: by mail-yb1-xb4a.google.com with SMTP id a16-20020a056902057000b00641c83f82f5so15015005ybt.22 for ; Tue, 19 Apr 2022 08:42:25 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=MWhERi4DU4hY8hbRinL5pU8MGWdCiSqvzarGWodqTns=; b=Xa96Vb4Y1Q8TZ6IS/+WURX2vOyOEXq0qysiGlErbZR+wWj9FIRQO0lf2cLaN+Jhh3O cHOIQrQZY4+rFkcEQ6GEUebsnHFTTCRLHMyUkmiHn95Fg0ERfSXGcQBSRA00v03pnxzs Ytw+gZ+zCPr3WTRky8ytoGgq4mvX0aAi45cqa1JCIpKCPoysDDFT7NaS52UWU3f9eYuZ X7emeJZmm3zc2Bp4PkF1/9tay7ZqWO0SQDl/iJ0vassyFCFDjCLdVk/8zeFxjwyG0I+v 8yC5dSNIK3hrRl8y/oAU4bbhr3U86KI7l1JVQ8bfcrDkhuNgEwzxBKnqxRBjql/Q4F4s /AEw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=MWhERi4DU4hY8hbRinL5pU8MGWdCiSqvzarGWodqTns=; b=WJNMmZCyJpWn0EoxVMJzIjm8qSPoTzgLp0CEuaT1jkH6glMB9UKrPhdLF0rVIlrU6C mUL4HMCoVPsVB5so5/A0uS8hehllHSjPrn/oKh4atRbkoxINAmy7wW9w9vR08CxRnFDt ufyVYCKKU6ZKVD7ASEz1r/1r8guIzAfdRc2y2t4Uqi49iwK5eQ96K9rBsUPbQPs3P41e vjEh8z8HM3NVmYbiu5p7wFIv6Xw2Ku25/8IGOXSdtnLAcKsHP3M2/Ad7ARVGviaR0Cfe avfNSXOCLxWeQQ2OvCETN1Jf2HjF/Fo4Xah2LQzOUrc0uroCiSZfBi9d514c5fH9Cl4a PtNw== X-Gm-Message-State: AOAM530dnllPJE7p05AT3rdwH8A7zVxlGBfX5gxxDNjQV9YpxTJhwwKM cj1AJ9IWFcg69gc+pDndVnh0rcU= X-Google-Smtp-Source: ABdhPJzQzBklYFPdivJ3Z8Gc+UNAXKFCXm1LGcfqQQMV0CEwQhuGOrZGcqeelvEOosukbybSFgjATOs= X-Received: from sdf2.svl.corp.google.com ([2620:15c:2c4:201:37f:6746:8e66:a291]) (user=sdf job=sendgmr) by 2002:a81:ad47:0:b0:2ee:927d:ff39 with SMTP id l7-20020a81ad47000000b002ee927dff39mr16281999ywk.249.1650382944389; Tue, 19 Apr 2022 08:42:24 -0700 (PDT) Date: Tue, 19 Apr 2022 08:42:21 -0700 In-Reply-To: Message-Id: Mime-Version: 1.0 References: <20220414161233.170780-1-sdf@google.com> Subject: Re: [PATCH bpf-next v2] bpf: move rcu lock management out of BPF_PROG_RUN routines From: sdf@google.com To: Alexei Starovoitov Cc: Network Development , bpf , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau Content-Type: text/plain; charset="UTF-8"; format=flowed; delsp=yes Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 04/18, Alexei Starovoitov wrote: > On Mon, Apr 18, 2022 at 9:50 AM wrote: > > > > On 04/16, Alexei Starovoitov wrote: > > > On Thu, Apr 14, 2022 at 9:12 AM Stanislav Fomichev > 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 > Hmm. I'm not sure how you've got this asm. > Here is what I see with gcc 8 and gcc 10: > bpf_prog_run_array_cg: > ... > movq %rcx, %r12 # run_prog, run_prog > ... > # ../kernel/bpf/cgroup.c:77: run_ctx.prog_item = item; > movq %rbx, (%rsp) # item, run_ctx.prog_item > # ../kernel/bpf/cgroup.c:78: if (!run_prog(prog, ctx) && > !IS_ERR_VALUE((long)run_ctx.retval)) > movq %rbp, %rsi # ctx, > call *%r12 # run_prog > __cgroup_bpf_run_filter_sk: > movq $bpf_prog_run, %rcx #, > # ../kernel/bpf/cgroup.c:1202: return > bpf_prog_run_array_cg(&cgrp->bpf, atype, sk, bpf_prog_run, 0); > leaq 1520(%rax), %rdi #, tmp92 > # ../kernel/bpf/cgroup.c:1202: return > bpf_prog_run_array_cg(&cgrp->bpf, atype, sk, bpf_prog_run, 0); > jmp bpf_prog_run_array_cg # > This is without kasan, lockdep and all debug configs are off. > So the generated code is pretty bad as I predicted :( > So I'm afraid this approach is no go. I've retested again and it still unrolls it for me on gcc 11 :-/ Anyway, I guess we have two options: 1. Go back to defines. 2. Don't pass a ptr to func, but pass an enum which indicates whether to use bpf_prog_run or __bpf_prog_run_save_cb. Seems like in this case the compiler shouldn't have any trouble unwrapping it? I'll prototype and send (2). If it won't work out we can always get back to (1).