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=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 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 CA625C433E0 for ; Tue, 30 Jun 2020 14:44:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9D7162074F for ; Tue, 30 Jun 2020 14:44:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389062AbgF3On7 (ORCPT ); Tue, 30 Jun 2020 10:43:59 -0400 Received: from mx2.suse.de ([195.135.220.15]:58852 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726072AbgF3On7 (ORCPT ); Tue, 30 Jun 2020 10:43:59 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 06EF1AB3D; Tue, 30 Jun 2020 14:43:57 +0000 (UTC) Date: Tue, 30 Jun 2020 16:43:55 +0200 From: Michal =?iso-8859-1?Q?Such=E1nek?= To: Mike Snitzer Cc: Mikulas Patocka , linux-nvdimm@lists.01.org, "Aneesh Kumar K.V" , Jan Kara , Alasdair Kergon , dm-devel@redhat.com, "Michael S. Tsirkin" , Yuval Shaia , Cornelia Huck , Jakub Staron , linux-kernel@vger.kernel.org Subject: Re: dm writecache: reject asynchronous pmem. Message-ID: <20200630144355.GA21462@kitsune.suse.cz> References: <20200630123528.29660-1-msuchanek@suse.de> <20200630141022.GZ21462@kitsune.suse.cz> <20200630133546.GA20439@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20200630133546.GA20439@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 30, 2020 at 09:36:33AM -0400, Mike Snitzer wrote: > On Tue, Jun 30 2020 at 10:10am -0400, > Michal Suchánek wrote: > > > On Tue, Jun 30, 2020 at 09:32:01AM -0400, Mikulas Patocka wrote: > > > > > > > > > On Tue, 30 Jun 2020, Michal Suchanek wrote: > > > > > > > The writecache driver does not handle asynchronous pmem. Reject it when > > > > supplied as cache. > > > > > > > > Link: https://lore.kernel.org/linux-nvdimm/87lfk5hahc.fsf@linux.ibm.com/ > > > > Fixes: 6e84200c0a29 ("virtio-pmem: Add virtio pmem driver") > > > > > > > > Signed-off-by: Michal Suchanek > > > > --- > > > > drivers/md/dm-writecache.c | 6 ++++++ > > > > 1 file changed, 6 insertions(+) > > > > > > > > diff --git a/drivers/md/dm-writecache.c b/drivers/md/dm-writecache.c > > > > index 30505d70f423..57b0a972f6fd 100644 > > > > --- a/drivers/md/dm-writecache.c > > > > +++ b/drivers/md/dm-writecache.c > > > > @@ -2277,6 +2277,12 @@ static int writecache_ctr(struct dm_target *ti, unsigned argc, char **argv) > > > > > > > > wc->memory_map_size -= (uint64_t)wc->start_sector << SECTOR_SHIFT; > > > > > > > > + if (!dax_synchronous(wc->ssd_dev->dax_dev)) { > > > > + r = -EOPNOTSUPP; > > > > + ti->error = "Asynchronous persistent memory not supported as pmem cache"; > > > > + goto bad; > > > > + } > > > > + > > > > bio_list_init(&wc->flush_list); > > > > wc->flush_thread = kthread_create(writecache_flush_thread, wc, "dm_writecache_flush"); > > > > if (IS_ERR(wc->flush_thread)) { > > > > -- > > > > > > Hi > > > > > > Shouldn't this be in the "if (WC_MODE_PMEM(wc))" block? > > That should be always the case at this point. > > > > > > WC_MODE_PMEM(wc) retrurns true if we are using persistent memory as a > > > cache device, otherwise we are using generic block device as a cache > > > device. > > > > This is to prevent the situation where we have WC_MODE_PMEM(wc) but > > cannot guarantee consistency because the async flush is not handled. > > The writecache operates in 2 modes. SSD or PMEM. Mikulas is saying > your dax_synchronous() check should go within a WC_MODE_PMEM(wc) block > because it doesn't make sense to do the check when in SSD mode. Indeed, it's in the wrong if/else branch. Thanks Michal