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 6590AC00140 for ; Fri, 19 Aug 2022 00:07:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239037AbiHSAHT (ORCPT ); Thu, 18 Aug 2022 20:07:19 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51386 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234482AbiHSAHR (ORCPT ); Thu, 18 Aug 2022 20:07:17 -0400 Received: from smtp-fw-9102.amazon.com (smtp-fw-9102.amazon.com [207.171.184.29]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 49D4EC7FBC; Thu, 18 Aug 2022 17:07:16 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazon201209; t=1660867637; x=1692403637; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=SaRfa3u26PjTQ23fCghirKypq5/HaGgCZmKXwPI3ZTs=; b=U1vxZMT5A9XD3/jgm7SUwGJ14bsWZvRLQHGePIjYqWrkZz73D3r7tU0f dmlZmp4gDybaoSlihXkWcJKV8pFaoNmI5anl17Whz2E2tCydSst4Xjcig tvTDzPq+nxQxLFykrJei1fZHB/hTGdtX3q25RqZTItOmri/mcM0Z6UZ8m k=; X-IronPort-AV: E=Sophos;i="5.93,247,1654560000"; d="scan'208";a="250466127" Received: from pdx4-co-svc-p1-lb2-vlan2.amazon.com (HELO email-inbound-relay-iad-1e-8be8ed69.us-east-1.amazon.com) ([10.25.36.210]) by smtp-border-fw-9102.sea19.amazon.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Aug 2022 00:07:01 +0000 Received: from EX13MTAUWB001.ant.amazon.com (iad12-ws-svc-p26-lb9-vlan3.iad.amazon.com [10.40.163.38]) by email-inbound-relay-iad-1e-8be8ed69.us-east-1.amazon.com (Postfix) with ESMTPS id 79894C0AB4; Fri, 19 Aug 2022 00:06:59 +0000 (UTC) Received: from EX19D004ANA001.ant.amazon.com (10.37.240.138) by EX13MTAUWB001.ant.amazon.com (10.43.161.207) with Microsoft SMTP Server (TLS) id 15.0.1497.38; Fri, 19 Aug 2022 00:06:56 +0000 Received: from 88665a182662.ant.amazon.com.com (10.43.162.85) by EX19D004ANA001.ant.amazon.com (10.37.240.138) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.1118.12; Fri, 19 Aug 2022 00:06:54 +0000 From: Kuniyuki Iwashima To: CC: , , , , , , Subject: Re: [PATCH v1 bpf 1/4] bpf: Fix data-races around bpf_jit_enable. Date: Thu, 18 Aug 2022 17:06:45 -0700 Message-ID: <20220819000645.55413-1-kuniyu@amazon.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-Originating-IP: [10.43.162.85] X-ClientProxiedBy: EX13D30UWB001.ant.amazon.com (10.43.161.80) To EX19D004ANA001.ant.amazon.com (10.37.240.138) Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org From: Alexei Starovoitov Date: Thu, 18 Aug 2022 15:49:46 -0700 > On Wed, Aug 17, 2022 at 9:24 PM Kuniyuki Iwashima wrote: > > > > A sysctl variable bpf_jit_enable is accessed concurrently, and there is > > always a chance of data-race. So, all readers and a writer need some > > basic protection to avoid load/store-tearing. > > > > Fixes: 0a14842f5a3c ("net: filter: Just In Time compiler for x86-64") > > Signed-off-by: Kuniyuki Iwashima > > --- > > arch/arm/net/bpf_jit_32.c | 2 +- > > arch/arm64/net/bpf_jit_comp.c | 2 +- > > arch/mips/net/bpf_jit_comp.c | 2 +- > > arch/powerpc/net/bpf_jit_comp.c | 5 +++-- > > arch/riscv/net/bpf_jit_core.c | 2 +- > > arch/s390/net/bpf_jit_comp.c | 2 +- > > arch/sparc/net/bpf_jit_comp_32.c | 5 +++-- > > arch/sparc/net/bpf_jit_comp_64.c | 5 +++-- > > arch/x86/net/bpf_jit_comp.c | 2 +- > > arch/x86/net/bpf_jit_comp32.c | 2 +- > > include/linux/filter.h | 2 +- > > net/core/sysctl_net_core.c | 4 ++-- > > 12 files changed, 19 insertions(+), 16 deletions(-) > > > > diff --git a/arch/arm/net/bpf_jit_32.c b/arch/arm/net/bpf_jit_32.c > > index 6a1c9fca5260..4b6b62a6fdd4 100644 > > --- a/arch/arm/net/bpf_jit_32.c > > +++ b/arch/arm/net/bpf_jit_32.c > > @@ -1999,7 +1999,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog) > > } > > flush_icache_range((u32)header, (u32)(ctx.target + ctx.idx)); > > > > - if (bpf_jit_enable > 1) > > + if (READ_ONCE(bpf_jit_enable) > 1) > > Nack. > Even if the compiler decides to use single byte loads for some > odd reason there is no issue here. I see, and same for 2nd/3rd patches, right? Then how about this part? It's not data-race nor problematic in practice, but should the value be consistent in the same function? The 2nd/3rd patches also have this kind of part. ---8<--- diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c index 43e634126514..c71d1e94ee7e 100644 --- a/arch/powerpc/net/bpf_jit_comp.c +++ b/arch/powerpc/net/bpf_jit_comp.c @@ -122,6 +122,7 @@ bool bpf_jit_needs_zext(void) struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp) { + int jit_enable = READ_ONCE(bpf_jit_enable); u32 proglen; u32 alloclen; u8 *image = NULL; @@ -263,13 +264,13 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp) } bpf_jit_build_epilogue(code_base, &cgctx); - if (bpf_jit_enable > 1) + if (jit_enable > 1) pr_info("Pass %d: shrink = %d, seen = 0x%x\n", pass, proglen - (cgctx.idx * 4), cgctx.seen); } skip_codegen_passes: - if (bpf_jit_enable > 1) + if (jit_enable > 1) /* * Note that we output the base address of the code_base * rather than image, since opcodes are in code_base. ---8<---