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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 0D6F5C7618B for ; Fri, 26 Jul 2019 13:50:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E57AF22CE5 for ; Fri, 26 Jul 2019 13:50:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387971AbfGZNt4 (ORCPT ); Fri, 26 Jul 2019 09:49:56 -0400 Received: from mail-qt1-f194.google.com ([209.85.160.194]:44444 "EHLO mail-qt1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388448AbfGZNtt (ORCPT ); Fri, 26 Jul 2019 09:49:49 -0400 Received: by mail-qt1-f194.google.com with SMTP id 44so21601466qtg.11 for ; Fri, 26 Jul 2019 06:49:49 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:content-transfer-encoding :in-reply-to; bh=Arc7jiA/gNfqVVW7QNfgaMfkpV6mHYMiv3nUsNQh21Q=; b=hmLc8zO2nsV32cS7oIazq0jXP+3Jiypbryu819U9INWcwiTnH5OXUcXJfVaQD3SvS5 0qwicvQMXDDO8DyWNSa0HjSMhyi9JkRZiA1W9qmzMoAJguI9PA8yQUmQj4welY3Av6tn 18ZT/JSF9ONdfZkJCrTfJr+XpvaMY9h2toTWNT818zfsxrZUNvfAup2aQqU55ScYCgwd xw0MR6jw+n/d1hlgPCgk23hk8lKDULP7LAuDZ/1NB2QrFAVzLuqHcztUChlR46G+wEM2 HmgoGqM4nCH5C7bNWp0I5/AUF8iYj7OkA9iJqshfcgmRQIvGT1hMYGVIfT8T6b6n467K xYjg== X-Gm-Message-State: APjAAAW9aSHPn3YGmOV6OikxrkD9XgW7Ru/Tw3SMVrTYr65f4APutflO a+lX1l225MaTQjbGPDwzwKzXyg== X-Google-Smtp-Source: APXvYqwJQHLCc1j1lFY5aAZTn5kwYloU8xFZNwjN11XBjJ1dY1OXNTBegRGc33x5aUh2wiZJ7uMG3w== X-Received: by 2002:a0c:9233:: with SMTP id a48mr67054287qva.66.1564148988892; Fri, 26 Jul 2019 06:49:48 -0700 (PDT) Received: from redhat.com ([212.92.104.165]) by smtp.gmail.com with ESMTPSA id w19sm20959381qkj.66.2019.07.26.06.49.42 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Fri, 26 Jul 2019 06:49:48 -0700 (PDT) Date: Fri, 26 Jul 2019 09:49:39 -0400 From: "Michael S. Tsirkin" To: Jason Wang Cc: syzbot , aarcange@redhat.com, akpm@linux-foundation.org, christian@brauner.io, davem@davemloft.net, ebiederm@xmission.com, elena.reshetova@intel.com, guro@fb.com, hch@infradead.org, james.bottomley@hansenpartnership.com, jglisse@redhat.com, keescook@chromium.org, ldv@altlinux.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-parisc@vger.kernel.org, luto@amacapital.net, mhocko@suse.com, mingo@kernel.org, namit@vmware.com, peterz@infradead.org, syzkaller-bugs@googlegroups.com, viro@zeniv.linux.org.uk, wad@chromium.org Subject: Re: WARNING in __mmdrop Message-ID: <20190726094756-mutt-send-email-mst@kernel.org> References: <55e8930c-2695-365f-a07b-3ad169654d28@redhat.com> <20190725042651-mutt-send-email-mst@kernel.org> <84bb2e31-0606-adff-cf2a-e1878225a847@redhat.com> <20190725092332-mutt-send-email-mst@kernel.org> <11802a8a-ce41-f427-63d5-b6a4cf96bb3f@redhat.com> <20190726074644-mutt-send-email-mst@kernel.org> <5cc94f15-b229-a290-55f3-8295266edb2b@redhat.com> <20190726082837-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Sender: linux-parisc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-parisc@vger.kernel.org On Fri, Jul 26, 2019 at 09:36:18PM +0800, Jason Wang wrote: > > On 2019/7/26 下午8:53, Jason Wang wrote: > > > > On 2019/7/26 下午8:38, Michael S. Tsirkin wrote: > > > On Fri, Jul 26, 2019 at 08:00:58PM +0800, Jason Wang wrote: > > > > On 2019/7/26 下午7:49, Michael S. Tsirkin wrote: > > > > > On Thu, Jul 25, 2019 at 10:25:25PM +0800, Jason Wang wrote: > > > > > > On 2019/7/25 下午9:26, Michael S. Tsirkin wrote: > > > > > > > > Exactly, and that's the reason actually I use > > > > > > > > synchronize_rcu() there. > > > > > > > > > > > > > > > > So the concern is still the possible synchronize_expedited()? > > > > > > > I think synchronize_srcu_expedited. > > > > > > > > > > > > > > synchronize_expedited sends lots of IPI and is bad for realtime VMs. > > > > > > > > > > > > > > > Can I do this > > > > > > > > on through another series on top of the incoming V2? > > > > > > > > > > > > > > > > Thanks > > > > > > > > > > > > > > > The question is this: is this still a gain if we switch to the > > > > > > > more expensive srcu? If yes then we can keep the feature on, > > > > > > I think we only care about the cost on srcu_read_lock() > > > > > > which looks pretty > > > > > > tiny form my point of view. Which is basically a > > > > > > READ_ONCE() + WRITE_ONCE(). > > > > > > > > > > > > Of course I can benchmark to see the difference. > > > > > > > > > > > > > > > > > > > if not we'll put it off until next release and think > > > > > > > of better solutions. rcu->srcu is just a find and replace, > > > > > > > don't see why we need to defer that. can be a separate patch > > > > > > > for sure, but we need to know how well it works. > > > > > > I think I get here, let me try to do that in V2 and > > > > > > let's see the numbers. > > > > > > > > > > > > Thanks > > > > > > > > It looks to me for tree rcu, its srcu_read_lock() have a mb() > > > > which is too > > > > expensive for us. > > > I will try to ponder using vq lock in some way. > > > Maybe with trylock somehow ... > > > > > > Ok, let me retry if necessary (but I do remember I end up with deadlocks > > last try). > > > Ok, I play a little with this. And it works so far. Will do more testing > tomorrow. > > One reason could be I switch to use get_user_pages_fast() to > __get_user_pages_fast() which doesn't need mmap_sem. > > Thanks OK that sounds good. If we also set a flag to make vhost_exceeds_weight exit, then I think it will be all good. -- MST 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=-0.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=no 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 2BCA3C76190 for ; Fri, 26 Jul 2019 13:49:54 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 059DA22CD8 for ; Fri, 26 Jul 2019 13:49:53 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="MqBDHyLA" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 059DA22CD8 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=WXG0k9AjSgDPn7UkLTO8mzQ4sfI1v91kpRkKjk8r5DA=; b=MqBDHyLA0t+qqk P+GowVR+xBifD0L2rqJKog4j8vCOxQ2pSI5wdmOjKmbZii0ZK1txPtCLLVXpEawQxftvXZjOsSADX W38xuNcwiwGnmMUxSn+F2XZENRZ8+4sgxq3qR03FFbrLFY79+h1jYpJTlEkC02qqpS6mqxrIBO0FE Uw2PA6o3+nSIPl23bkbPNgjc21ShcmoUH5D1A5MFg8x5TQvSM66Qow+rFXmDVdKIvRtZr6hswd5Kd SVy3ypeAiEWeKjQhiyJI6+4UTAaePd8DSW3oGwYAlYaCAE2xc89rhyXM4i/kxD5fj9BB7gMnaQ/fd l2hLqdku3e5ob0EMAVFw==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hr0bZ-0005tc-FT; Fri, 26 Jul 2019 13:49:53 +0000 Received: from mail-qt1-f194.google.com ([209.85.160.194]) by bombadil.infradead.org with esmtps (Exim 4.92 #3 (Red Hat Linux)) id 1hr0bV-0005sw-K4 for linux-arm-kernel@lists.infradead.org; Fri, 26 Jul 2019 13:49:50 +0000 Received: by mail-qt1-f194.google.com with SMTP id l9so52585434qtu.6 for ; Fri, 26 Jul 2019 06:49:49 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:content-transfer-encoding :in-reply-to; bh=Arc7jiA/gNfqVVW7QNfgaMfkpV6mHYMiv3nUsNQh21Q=; b=VrrHDHNpsc+vyibC8NlSUPgsG9JCO0Ra8feYhaHNvaUFlOOQD9pKz80Q2PQmFvbrWG A+U3q8jdiLPzn5eZfyUift2T1qYz+SABAKPMStjKxVMtcAWa1Hyg9dnOErO0jpnB2LKC 0TJpeO9ZekzlyeUI0llTQlYA5uKRtqCtr5vULefTswKG/DuwCzXHunycEFh1pKvdJsFw uvAQPGqmAcZS/QRTbMpbgEE9SaTdhnJqIT9MhK8rhgEIg1p468zInuchzjHEv/sR1NyY uAjwcwl2+yZUxNBcxaJ+vp4BU2MoD3ioF5yfOwCc2qMHGpiRX9q899HLlgQ9EqTANUga t/9g== X-Gm-Message-State: APjAAAUJ+NeiHqCnjiixmc2nngzZMzWMKJM3wJrkhA1VoWlLNiALB4jd giHW243KBDjBcwZZowD5q98yDA== X-Google-Smtp-Source: APXvYqwJQHLCc1j1lFY5aAZTn5kwYloU8xFZNwjN11XBjJ1dY1OXNTBegRGc33x5aUh2wiZJ7uMG3w== X-Received: by 2002:a0c:9233:: with SMTP id a48mr67054287qva.66.1564148988892; Fri, 26 Jul 2019 06:49:48 -0700 (PDT) Received: from redhat.com ([212.92.104.165]) by smtp.gmail.com with ESMTPSA id w19sm20959381qkj.66.2019.07.26.06.49.42 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Fri, 26 Jul 2019 06:49:48 -0700 (PDT) Date: Fri, 26 Jul 2019 09:49:39 -0400 From: "Michael S. Tsirkin" To: Jason Wang Subject: Re: WARNING in __mmdrop Message-ID: <20190726094756-mutt-send-email-mst@kernel.org> References: <55e8930c-2695-365f-a07b-3ad169654d28@redhat.com> <20190725042651-mutt-send-email-mst@kernel.org> <84bb2e31-0606-adff-cf2a-e1878225a847@redhat.com> <20190725092332-mutt-send-email-mst@kernel.org> <11802a8a-ce41-f427-63d5-b6a4cf96bb3f@redhat.com> <20190726074644-mutt-send-email-mst@kernel.org> <5cc94f15-b229-a290-55f3-8295266edb2b@redhat.com> <20190726082837-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190726_064949_660978_CDC2F7DD X-CRM114-Status: GOOD ( 24.14 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: mhocko@suse.com, peterz@infradead.org, ldv@altlinux.org, james.bottomley@hansenpartnership.com, linux-mm@kvack.org, namit@vmware.com, mingo@kernel.org, elena.reshetova@intel.com, keescook@chromium.org, aarcange@redhat.com, davem@davemloft.net, hch@infradead.org, christian@brauner.io, syzbot , syzkaller-bugs@googlegroups.com, jglisse@redhat.com, viro@zeniv.linux.org.uk, linux-arm-kernel@lists.infradead.org, wad@chromium.org, linux-parisc@vger.kernel.org, linux-kernel@vger.kernel.org, luto@amacapital.net, ebiederm@xmission.com, akpm@linux-foundation.org, guro@fb.com Content-Type: text/plain; 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