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=-6.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 A15FDC433B4 for ; Mon, 26 Apr 2021 00:49:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 59E4861041 for ; Mon, 26 Apr 2021 00:49:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231403AbhDZAui (ORCPT ); Sun, 25 Apr 2021 20:50:38 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:50385 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231247AbhDZAui (ORCPT ); Sun, 25 Apr 2021 20:50:38 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1619398197; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=dwxmnzj2l32bEs+ERvIucHwyR58dm5h6uygjcfXO8BY=; b=LxVdelYXNS29RfxadqeYF9r3DBM/3dNtj6m2mFXgiBrVG14XaAyxLFmzop6Tp2tpHutQlT hUTE9U4x/s55bL+M9FyXqGZEZQcsepUbHlu1fMFBXt0VcTGZ/+pa9Rp0fqYpUVXEaE+hAz R9uHUDhxSbp/535Yu8FTQHJDyKjg9GI= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-455-kCWv3Sh2OC-q5JtJmqHiXA-1; Sun, 25 Apr 2021 20:49:54 -0400 X-MC-Unique: kCWv3Sh2OC-q5JtJmqHiXA-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id D5747343A5; Mon, 26 Apr 2021 00:49:52 +0000 (UTC) Received: from T590 (ovpn-12-48.pek2.redhat.com [10.72.12.48]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 6AF7A5D9DC; Mon, 26 Apr 2021 00:49:43 +0000 (UTC) Date: Mon, 26 Apr 2021 08:49:48 +0800 From: Ming Lei To: Bart Van Assche Cc: linux-nvme@lists.infradead.org, linux-scsi@vger.kernel.org, Jens Axboe , linux-block@vger.kernel.org, "Martin K . Petersen" , Christoph Hellwig , Khazhy Kumykov , Shin'ichiro Kawasaki , Hannes Reinecke , John Garry , David Jeffery Subject: Re: [PATCH 8/8] blk-mq: clear stale request in tags->rq[] before freeing one request pool Message-ID: References: <20210425085753.2617424-1-ming.lei@redhat.com> <20210425085753.2617424-9-ming.lei@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Sun, Apr 25, 2021 at 01:42:59PM -0700, Bart Van Assche wrote: > On 4/25/21 1:57 AM, Ming Lei wrote: > > + spin_lock_irqsave(&drv_tags->lock, flags); > > + list_for_each_entry(page, &tags->page_list, lru) { > > + unsigned long start = (unsigned long)page_address(page); > > + unsigned long end = start + order_to_size(page->private); > > + int i; > > + > > + for (i = 0; i < set->queue_depth; i++) { > > + struct request *rq = drv_tags->rqs[i]; > > + unsigned long rq_addr = (unsigned long)rq; > > + > > + if (rq_addr >= start && rq_addr < end) { > > + WARN_ON_ONCE(refcount_read(&rq->ref) != 0); > > + cmpxchg(&drv_tags->rqs[i], rq, NULL); > > + } > > + } > > + } > > + spin_unlock_irqrestore(&drv_tags->lock, flags); > > Using cmpxchg() on set->tags[] is only safe if all other set->tags[] > accesses are changed into WRITE_ONCE() or READ_ONCE(). Why? Semantic of cmpxchg() is to modify value pointed by the address if its old value is same with passed 'rq'. That is exactly what we need. writting 'void *' is always atomic. if someone has touched '->rqs[tag]', cmpxchg() won't modify the value. Thanks, Ming 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=-4.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,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 AC36FC433ED for ; Mon, 26 Apr 2021 00:50:25 +0000 (UTC) Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (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 28555611C9 for ; Mon, 26 Apr 2021 00:50:25 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 28555611C9 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-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=desiato.20200630; h=Sender:Content-Transfer-Encoding :Content-Type:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:Cc: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=mS6McWWPYnpswrl4fX+PkyxhC71J7tOaBsPRA8zC5lE=; b=L8rhcCv/Gdzh9f/1zlLe/Ijh5 s2i9DSqNB6tfR5GKUbceu/PKRcoaIv2SEPPSIR5Xi4svOsTScnLpy6by8M3ebHsDajSp/4rWuH24v UlRgzuDgeT2nhjD9Q4kN91ySRVMoozM9KDGHL/P7gLPKblkOzltckENTXlw4UVTng35BQbBHehY5x hSLdctI5a9OMRxxP/foT2jup3j7WSmEAohRKL4pZZv71Sd5zhq5XspIzIigdzUQx/pk0YUj8kDlfb jS+H+3hALo9WIWBERIxd3IsbFze+mpfMz1IuOLDHklyF008PzGN4GiLaobaKS0s8yozO4dAQhDxfK hq8LyYL5Q==; Received: from localhost ([::1] helo=desiato.infradead.org) by desiato.infradead.org with esmtp (Exim 4.94 #2 (Red Hat Linux)) id 1lapRr-006Z6n-Vi; Mon, 26 Apr 2021 00:50:04 +0000 Received: from bombadil.infradead.org ([2607:7c80:54:e::133]) by desiato.infradead.org with esmtps (Exim 4.94 #2 (Red Hat Linux)) id 1lapRp-006Z6K-HH for linux-nvme@desiato.infradead.org; Mon, 26 Apr 2021 00:50:01 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; 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; bh=dwxmnzj2l32bEs+ERvIucHwyR58dm5h6uygjcfXO8BY=; b=4BDinRYMPAzUFCOktXmObrd0Sd tJ1Uu3gwK2kaRx9VfsYkg6EXaySs+4rb40ji+iPhg8WlJ9RbbMThdudAj3jn2Fu4CnDNva3jKCnlw nEGUUt9Y70BvvghEzy9gN7S2yv84h/kuQpZWrBJSntbKBeKGS4wqOWhFmkUtUHsFnckQiZarUleco yc19AvUs8btdxFd7O/DHqfdMRBiKDunnsvn6+QSL0iSlIimJMPizXKOSN/0v3TJbADRfOzzQn5Cl0 anYBMbJ+X9NSpb/tsSj/wnsSDkkv8fFl2fyGhaw8C4f7rBxQEzC17a0MeAnStNlRGqBB7ySGfndJJ aCh7gjNA==; Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]) by bombadil.infradead.org with esmtps (Exim 4.94 #2 (Red Hat Linux)) id 1lapRm-00FfnZ-Ql for linux-nvme@lists.infradead.org; Mon, 26 Apr 2021 00:50:00 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1619398197; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=dwxmnzj2l32bEs+ERvIucHwyR58dm5h6uygjcfXO8BY=; b=LxVdelYXNS29RfxadqeYF9r3DBM/3dNtj6m2mFXgiBrVG14XaAyxLFmzop6Tp2tpHutQlT hUTE9U4x/s55bL+M9FyXqGZEZQcsepUbHlu1fMFBXt0VcTGZ/+pa9Rp0fqYpUVXEaE+hAz R9uHUDhxSbp/535Yu8FTQHJDyKjg9GI= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-455-kCWv3Sh2OC-q5JtJmqHiXA-1; Sun, 25 Apr 2021 20:49:54 -0400 X-MC-Unique: kCWv3Sh2OC-q5JtJmqHiXA-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id D5747343A5; Mon, 26 Apr 2021 00:49:52 +0000 (UTC) Received: from T590 (ovpn-12-48.pek2.redhat.com [10.72.12.48]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 6AF7A5D9DC; Mon, 26 Apr 2021 00:49:43 +0000 (UTC) Date: Mon, 26 Apr 2021 08:49:48 +0800 From: Ming Lei To: Bart Van Assche Cc: linux-nvme@lists.infradead.org, linux-scsi@vger.kernel.org, Jens Axboe , linux-block@vger.kernel.org, "Martin K . Petersen" , Christoph Hellwig , Khazhy Kumykov , Shin'ichiro Kawasaki , Hannes Reinecke , John Garry , David Jeffery Subject: Re: [PATCH 8/8] blk-mq: clear stale request in tags->rq[] before freeing one request pool Message-ID: References: <20210425085753.2617424-1-ming.lei@redhat.com> <20210425085753.2617424-9-ming.lei@redhat.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210425_174958_963988_1776DAEF X-CRM114-Status: GOOD ( 14.68 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org On Sun, Apr 25, 2021 at 01:42:59PM -0700, Bart Van Assche wrote: > On 4/25/21 1:57 AM, Ming Lei wrote: > > + spin_lock_irqsave(&drv_tags->lock, flags); > > + list_for_each_entry(page, &tags->page_list, lru) { > > + unsigned long start = (unsigned long)page_address(page); > > + unsigned long end = start + order_to_size(page->private); > > + int i; > > + > > + for (i = 0; i < set->queue_depth; i++) { > > + struct request *rq = drv_tags->rqs[i]; > > + unsigned long rq_addr = (unsigned long)rq; > > + > > + if (rq_addr >= start && rq_addr < end) { > > + WARN_ON_ONCE(refcount_read(&rq->ref) != 0); > > + cmpxchg(&drv_tags->rqs[i], rq, NULL); > > + } > > + } > > + } > > + spin_unlock_irqrestore(&drv_tags->lock, flags); > > Using cmpxchg() on set->tags[] is only safe if all other set->tags[] > accesses are changed into WRITE_ONCE() or READ_ONCE(). Why? Semantic of cmpxchg() is to modify value pointed by the address if its old value is same with passed 'rq'. That is exactly what we need. writting 'void *' is always atomic. if someone has touched '->rqs[tag]', cmpxchg() won't modify the value. Thanks, Ming _______________________________________________ Linux-nvme mailing list Linux-nvme@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-nvme