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 X-Spam-Level: X-Spam-Status: No, score=-2.1 required=3.0 tests=DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,T_DKIM_INVALID, USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 980E7C433F4 for ; Thu, 30 Aug 2018 20:45:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 51806205F4 for ; Thu, 30 Aug 2018 20:45:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="CRAIUUrW" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 51806205F4 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727486AbeHaAtW (ORCPT ); Thu, 30 Aug 2018 20:49:22 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:33554 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725893AbeHaAtW (ORCPT ); Thu, 30 Aug 2018 20:49:22 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=Cjky/mM1tjSK/MV1yu9uHtt6HigDi4I+7M1zq65dyMg=; b=CRAIUUrWqXf+NZL/BkReCCWUQ jkClMthPDm9mrWlk/LUh/aYKf0xhGtiQlL940iS9VDtI7aymZffu/QolYEfild8n9mGxIjuxh9cZe Vu2GFwYSGZDPXjDmrw3/Y/WV+6K0Bws9zHPlMU5DwBj81rlsAM66/28Udhp83aFuaJTZBAleF+ZEI n+EXKi+fiOVxXkZH/MsVzC+mgQa+OLjFmzKfDuIPwIgqfUOkR+CO/m/6Ojgj0dmKyDSVvfok06iOR qC9KRz+sGrQn0uEmkvUjZf9hJcOtX2QPRQ/d7OqUMUOc2vXrQVuI2AC+GWtrEz3Xh4YjCin8uOz/3 pbzpmN6Lw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1fvTob-0007Ym-Bn; Thu, 30 Aug 2018 20:45:17 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id AF59820255987; Thu, 30 Aug 2018 22:45:15 +0200 (CEST) Date: Thu, 30 Aug 2018 22:45:15 +0200 From: Peter Zijlstra To: Vineet Gupta Cc: Will Deacon , Eugeniy Paltsev , "mingo@kernel.org" , "linux-kernel@vger.kernel.org" , "Alexey.Brodkin@synopsys.com" , "tglx@linutronix.de" , "linux-snps-arc@lists.infradead.org" , "yamada.masahiro@socionext.com" , "linux-arm-kernel@lists.infradead.org" , "linux-arch@vger.kernel.org" Subject: Re: Patch "asm-generic/bitops/lock.h: Rewrite using atomic_fetch_" causes kernel crash Message-ID: <20180830204515.GC24124@hirez.programming.kicks-ass.net> References: <1535567633.4465.23.camel@synopsys.com> <20180830094411.GX24124@hirez.programming.kicks-ass.net> <20180830095148.GB5942@arm.com> <1535629996.4465.44.camel@synopsys.com> <20180830141713.GN24082@hirez.programming.kicks-ass.net> <20180830142354.GB13005@arm.com> <20180830142920.GO24082@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 30, 2018 at 08:31:59PM +0000, Vineet Gupta wrote: > On 08/30/2018 07:29 AM, Peter Zijlstra wrote: > > On Thu, Aug 30, 2018 at 03:23:55PM +0100, Will Deacon wrote: > > > >> Yes, that would be worth trying. However, I also just noticed that the > >> fetch-ops (which are now used to implement test_and_set_bit_lock()) seem > >> to be missing the backwards branch in the LL/SC case. Yet another diff > >> below. > >> > >> Will > >> > >> --->8 > >> > >> diff --git a/arch/arc/include/asm/atomic.h b/arch/arc/include/asm/atomic.h > >> index 4e0072730241..f06c5ed672b3 100644 > >> --- a/arch/arc/include/asm/atomic.h > >> +++ b/arch/arc/include/asm/atomic.h > >> @@ -84,7 +84,7 @@ static inline int atomic_fetch_##op(int i, atomic_t *v) \ > >> "1: llock %[orig], [%[ctr]] \n" \ > >> " " #asm_op " %[val], %[orig], %[i] \n" \ > >> " scond %[val], [%[ctr]] \n" \ > >> - " \n" \ > >> + " bnz 1b \n" \ > >> : [val] "=&r" (val), \ > >> [orig] "=&r" (orig) \ > >> : [ctr] "r" (&v->counter), \ > > ACK!! sorry about that, no idea how I messed that up. > > > > Also, once it all works, they should look at switching to _relaxed > > atomics for LL/SC. > > Indeed this is the mother of all issues, I tried and system is clearly hosed with > and works after. > What's amazing is the commit 4aef66c8ae9 which introduced it is from 2016 ;-) > Back then we had a retry branch with backoff stuff which I'd reverted for new > cores and the merge conflict somehow missed it. > > @PeterZ I'll create a patch with you as author ? do I need any formal sign offs, > acks etc ? Well, Will spotted it, give authorship to him, you have my ack per the above. > So after this there are 2 other things to be addresses / looked at still while we > are still here. > > 1. After 84c6591103db __clear_bit_lock() implementation will be broken (or atleast > not consistent with what we had after), do we need to reinstate it. > 2. Will's proposed change to remove the underlying issue, but the issue in #1 > remains ? No, like explained, for spinlock based atomics the issue _should_ not exist, and if you look at your atomic_set() implementation for that variant, you'll see it does the right thing by taking the lock. Basically atomic_set() for spinlock based atomics ends up being (void)atomic_xchg(). FWIW, also ACK on Will's patch to switch you over to asm-generic bitops entirely.