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[23.128.96.18]) by mx.google.com with ESMTP id r9si488045eji.262.2020.05.13.13.42.20; Wed, 13 May 2020 13:42:42 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@google.com header.s=20161025 header.b="t/LHvFU/"; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=google.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726201AbgEMNQJ (ORCPT + 99 others); Wed, 13 May 2020 09:16:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53254 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725925AbgEMNQI (ORCPT ); Wed, 13 May 2020 09:16:08 -0400 Received: from mail-ot1-x344.google.com (mail-ot1-x344.google.com [IPv6:2607:f8b0:4864:20::344]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 98B4CC061A0E for ; Wed, 13 May 2020 06:16:08 -0700 (PDT) Received: by mail-ot1-x344.google.com with SMTP id 63so5967510oto.8 for ; Wed, 13 May 2020 06:16:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=ccPCDIGO/E8Bs4gAGfnutXW1wbp7wpweTm7DNmF97Nw=; b=t/LHvFU/22qCKVdWh9xY8l9LFSJBwOw/eZn/HBv6h4Qe2s4rNjQLY2ENX8Jo+NsECz r1LThDjUDgu+VJXlpDwLUWuBvhVsMnfYwWkJkGtnkFcF4iDa5CPj0RQCVUSXQ6yIGPWb 76i5G37gPIlhqXpFEvAOsY5bf86SFFObY3u4phokCQ4bVO4JCg+W0ARwxFug2zG+OH4N Ktq8uyXEWvfQFova71p+/rDoK9hzllf+i1DjMkrb7/e4UIuIu91xxz5wAu68OoIZU7Nr n8dtiUFuHBnuxx71p9bT52roE/oZTXbX20xKY4NJh6e+NTr1qbXZMlXOCuDYVIAKG2Lf RY5Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=ccPCDIGO/E8Bs4gAGfnutXW1wbp7wpweTm7DNmF97Nw=; b=UKpV5JmeS2BwsbVbv2s0d7RkpgLflyBPlykxZnU0RRZWwNo0ZuwpfP2aMWSbBDZLXE uGWbuEf/Ut0Ve88pstDIFbTAMSha3UWrHuojmL3bL54M48OBWEhOcmBRDDyy/N5kXuGW jYWkeFXqw5To34zzgotPvMLjVkQ87sKkO5tVB66T1ovSVdyF7pIbKC1HOkuRWMqhiChW tXifb80mcNKzWp/EKafAfUvteI7K+qLTcv1MAVX6IVneka9c6zq9Zdfudxa+6Je7ecPm SICEX4I9RMaC87Kv7bob8Zoe6nza81u6pZtuw1vL+pJT536iIFTVxqx7r1X0H3XTbPjM 762Q== X-Gm-Message-State: AGi0PuYQdafx2/kKRfLOkawSWKW0aW+GjmZagY0YIAyUQUZCo+5Bfzg4 egsuAeA4sWeYY28MZ29Y4bDNVaf8bh1oEXcxR8hh0g== X-Received: by 2002:a9d:4a:: with SMTP id 68mr8825172ota.17.1589375767383; Wed, 13 May 2020 06:16:07 -0700 (PDT) MIME-Version: 1.0 References: <20200511204150.27858-1-will@kernel.org> <20200512081826.GE2978@hirez.programming.kicks-ass.net> <20200512190755.GL2957@hirez.programming.kicks-ass.net> <20200513111057.GN2957@hirez.programming.kicks-ass.net> <20200513123243.GO2957@hirez.programming.kicks-ass.net> <20200513124021.GB20278@willie-the-truck> In-Reply-To: <20200513124021.GB20278@willie-the-truck> From: Marco Elver Date: Wed, 13 May 2020 15:15:55 +0200 Message-ID: Subject: Re: [PATCH v5 00/18] Rework READ_ONCE() to improve codegen To: Will Deacon Cc: Peter Zijlstra , LKML , Thomas Gleixner , "Paul E. McKenney" , Ingo Molnar , Dmitry Vyukov Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 13 May 2020 at 14:40, Will Deacon wrote: > > On Wed, May 13, 2020 at 02:32:43PM +0200, Peter Zijlstra wrote: > > On Wed, May 13, 2020 at 01:48:41PM +0200, Marco Elver wrote: > > > > > Disabling most instrumentation for arch/x86 is reasonable. Also fine > > > with the __READ_ONCE/__WRITE_ONCE changes (your improved > > > compiler-friendlier version). > > > > > > We likely can't have both: still instrument __READ_ONCE/__WRITE_ONCE > > > (as Will suggested) *and* avoid double-instrumentation in arch_atomic. > > > If most use-cases of __READ_ONCE/__WRITE_ONCE are likely to use > > > data_race() or KCSAN_SANITIZE := n anyway, I'd say it's reasonable for > > > now. > > I agree that Peter's patch is the right thing to do for now. I was hoping we > could instrument __{READ,WRITE}_ONCE(), but that we before I realised that > __no_sanitize_or_inline doesn't seem to do anything. > > > Right, if/when people want sanitize crud enabled for x86 I need > > something that: > > > > - can mark a function 'no_sanitize' and all code that gets inlined into > > that function must automagically also not get sanitized. ie. make > > inline work like macros (again). > > > > And optionally: > > > > - can mark a function explicitly 'sanitize', and only when an explicit > > sanitize and no_sanitize mix in inlining give the current > > incompatible attribute splat. > > > > That way we can have the noinstr function attribute imply no_sanitize > > and frob the DEFINE_IDTENTRY*() macros to use (a new) sanitize_or_inline > > helper instead of __always_inline for __##func(). > > Sounds like a good plan to me, assuming the compiler folks are onboard. > In the meantime, can we kill __no_sanitize_or_inline and put it back to > the old __no_kasan_or_inline, which I think simplifies compiler.h and > doesn't mislead people into using the function annotation to avoid KCSAN? > > READ_ONCE_NOCHECK should also probably be READ_ONCE_NOKASAN, but I > appreciate that's a noisier change. So far so good, except: both __no_sanitize_or_inline and __no_kcsan_or_inline *do* avoid KCSAN instrumenting plain accesses, it just doesn't avoid explicit kcsan_check calls, like those in READ/WRITE_ONCE if KCSAN is enabled for the compilation unit. That's just because macros won't be redefined just for __no_sanitize functions. Similarly, READ_ONCE_NOCHECK does work as expected, and its access is unchecked. This will have the expected result: __no_sanitize_or_inline void foo(void) { x++; } // no data races reported This will not work as expected: __no_sanitize_or_inline void foo(void) { READ_ONCE(x); } // data races are reported All this could be fixed if GCC devs would finally take my patch to make -fsanitize=thread distinguish volatile [1], but then we have to wait ~years for the new compilers to reach us. So please don't hold your breath for this one any time soon. [1] https://gcc.gnu.org/pipermail/gcc-patches/2020-April/544452.html Thanks, -- Marco