From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx3-rdu2.redhat.com ([66.187.233.73]:49342 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751835AbeFAUTo (ORCPT ); Fri, 1 Jun 2018 16:19:44 -0400 Date: Fri, 1 Jun 2018 16:19:25 -0400 From: Mike Snitzer To: Ross Zwisler Cc: Toshi Kani , dm-devel@redhat.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nvdimm@lists.01.org, linux-xfs@vger.kernel.org Subject: Re: [PATCH v2 3/7] dm: fix test for DAX device support Message-ID: <20180601201924.GA1144@redhat.com> References: <20180529195106.14268-1-ross.zwisler@linux.intel.com> <20180529195106.14268-4-ross.zwisler@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180529195106.14268-4-ross.zwisler@linux.intel.com> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Tue, May 29 2018 at 3:51P -0400, Ross Zwisler wrote: > Currently device_supports_dax() just checks to see if the QUEUE_FLAG_DAX > flag is set on the device's request queue to decide whether or not the > device supports filesystem DAX. This is insufficient because there are > devices like PMEM namespaces in raw mode which have QUEUE_FLAG_DAX set but > which don't actually support DAX. Isn't that a PMEM bug then? What is the point of setting QUEUE_FLAG_DAX if it cannot be trusted? > This means that you could create a dm-linear device, for example, where the > first part of the dm-linear device was a PMEM namespace in fsdax mode and > the second part was a PMEM namespace in raw mode. Both DM and the > filesystem you put on that dm-linear device would think the whole device > supports DAX, which would lead to bad behavior once your raw PMEM namespace > part using DAX needed struct page for something. The PMEM namespace in raw mode shouldn't be setting QUEUE_FLAG_DAX, if it didn't then the stacked-up linear DM wouldn't > Fix this by using bdev_dax_supported() like filesystems do at mount time. > This checks for raw mode and also performs other tests like checking to > make sure the dax_direct_access() path works. Sorry "This" does those things where? > > Signed-off-by: Ross Zwisler > Fixes: commit 545ed20e6df6 ("dm: add infrastructure for DAX support") > --- > drivers/md/dm-table.c | 4 +--- > 1 file changed, 1 insertion(+), 3 deletions(-) > > diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c > index 0589a4da12bb..5bb994b012ca 100644 > --- a/drivers/md/dm-table.c > +++ b/drivers/md/dm-table.c > @@ -885,9 +885,7 @@ EXPORT_SYMBOL_GPL(dm_table_set_type); > static int device_supports_dax(struct dm_target *ti, struct dm_dev *dev, > sector_t start, sector_t len, void *data) > { > - struct request_queue *q = bdev_get_queue(dev->bdev); > - > - return q && blk_queue_dax(q); > + return bdev_dax_supported(dev->bdev, PAGE_SIZE); > } > > static bool dm_table_supports_dax(struct dm_table *t) > -- > 2.14.3 >