From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=213.95.11.211 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794490796; b=1Ojj2ZuBUN3hRw5WpEhtbI6b721pBhWHUgs++DJgbMsHP5Q7paDPEAimiebPR6gU/Pcn JK2Efa08zrb9n1NFsZNUP7pBK00k7B4Yyd0JWoEHWxnuCjPdSapSINfDIf7upGeQ27rxh /EGVJW7D2bX+1TT4L8mz6BaEUVnBvSpm5BXFICE0A5BmnB/fKTwwk7wbzWRuPqHnQqpu4 H+8F07EkKlogeUKutWBDKmMd8kfh/8GxTBgwGy0kNHgqkFDidyxkwmS14bq/ljXRUQjul Rioq97LWqfwzLaS2CG9KxjcuQuK5959oMvntL2B+PuOJw/RwUgnRLygiei10uXQouaA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794490796; h=DMARC-Filter:Received:Date:From:To:Cc:Subject:Message-ID:References: MIME-Version:Content-Type:Content-Disposition:In-Reply-To:User-Agent; bh=NQFIYysb2hWKuro6zw4pfUd0EAxD2lKYbXMorN8G9OA=; b=4auf83Dqd5CxxLTZ3tLQQpfnQC18nadAEBgn5Qo7uuv6+BZ0TMaYP113UEgdX4dxhemK Sy8Xo7HeZf0sVVSW1m/LePoZxc3alasoDrlW6WoSA94Z6JyuR/H0lc0SeqSCnNGUlawGC 5kdvx/C7OaDJu38ZyspxIKHZgrwKLpetrvTkbRyr18JbGpzNRLVCdmhijgCt4USh/ZVeG ZNBRMRryeTLRif6AgAvuzhgRfYcCL/nCabmf5FooZiYyT515i/103nZ9EMqE+dP31Ar6R QhNYbm+lqkxSAqi5/IV5jKBajpwxfdhil42yLl4+5F4Bfjt0Z33VtFVaoB0xGlqZQig== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=lst.de; spf=pass smtp.mailfrom=lst.de; arc=none smtp.remote-ip=213.95.11.211 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) (using TLSv1.2 with cipher ECDHE-ECDSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CB8A3606A335; Thu, 12 Nov 2026 13:39:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org CB8A3606A335 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=lst.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=lst.de Received: by verein.lst.de (Postfix, from userid 2407) id 6CF1F6732A; Thu, 12 Nov 2026 14:39:50 +0100 (CET) Date: Thu, 12 Nov 2026 14:39:50 +0100 From: Christoph Hellwig To: Chris Mason Cc: tytso@mit.edu, cem@kernel.org, david@fromorbit.com, jack@suse.cz, djwong@kernel.org, josef@toxicpanda.com, hch@lst.de, linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, tz2294@columbia.edu, brauner@kernel.org Subject: Re: [PATCH v8 15/15] xfs: don't enable DAX on zoned inodes Message-ID: <20261112133950.GE22165@lst.de> References: <20261112010229.51029-1-mason@kernel.org> <20261112010229.51029-16-mason@kernel.org> X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261112010229.51029-16-mason@kernel.org> User-Agent: Mutt/1.5.17 (2007-11-01) On Wed, Nov 11, 2026 at 08:02:44PM -0500, Chris Mason wrote: > A store through a shared mapping can dereference a NULL pointer if the > file is zoned and has S_DAX. > > DAX writes in place, DAX does not actually require in-place writes, we had patches to support DAX with reflink for example. > and zoned inodes are only written out of place, so > the two can't work together. XFS doesn't check for this: with dax=always > or FS_XFLAG_DAX, an inode gets S_DAX if its device does DAX, and an > internal zoned section on pmem does. The write fault then takes the > zoned path: > > xfs_filemap_fault() > xfs_write_fault() > xfs_write_fault_zoned() > page_folio(vmf->page) /* NULL in a DAX fault */ but this is real issue, and xfs_write_fault_zoned would need to find a way to deal with pfn faults. I think thi could be supported, but there's no real reason to bother as there is no good use yet (at least right now). So I think your change is fine, but the commit log and comments are not. Just say that the zone code does not support DAX, and maybe mention this callchain.