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