From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f70.google.com (mail-wm0-f70.google.com [74.125.82.70]) by kanga.kvack.org (Postfix) with ESMTP id 4FBB96B025E for ; Fri, 2 Dec 2016 05:08:23 -0500 (EST) Received: by mail-wm0-f70.google.com with SMTP id g23so2145986wme.4 for ; Fri, 02 Dec 2016 02:08:23 -0800 (PST) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id b188si2250273wme.154.2016.12.02.02.08.21 for (version=TLS1 cipher=AES128-SHA bits=128/128); Fri, 02 Dec 2016 02:08:22 -0800 (PST) Date: Fri, 2 Dec 2016 11:08:18 +0100 From: Jan Kara Subject: Re: [PATCH 5/6] dax: Call ->iomap_begin without entry lock during dax fault Message-ID: <20161202100818.GA26086@quack2.suse.cz> References: <1479980796-26161-1-git-send-email-jack@suse.cz> <1479980796-26161-6-git-send-email-jack@suse.cz> <20161201222447.GB13739@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161201222447.GB13739@linux.intel.com> Sender: owner-linux-mm@kvack.org List-ID: To: Ross Zwisler Cc: Jan Kara , linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-mm@kvack.org, linux-nvdimm@lists.01.org, Johannes Weiner On Thu 01-12-16 15:24:47, Ross Zwisler wrote: > On Thu, Nov 24, 2016 at 10:46:35AM +0100, Jan Kara wrote: > > Currently ->iomap_begin() handler is called with entry lock held. If the > > filesystem held any locks between ->iomap_begin() and ->iomap_end() > > (such as ext4 which will want to hold transaction open), this would cause > > lock inversion with the iomap_apply() from standard IO path which first > > calls ->iomap_begin() and only then calls ->actor() callback which grabs > > entry locks for DAX. > > I don't see the dax_iomap_actor() grabbing any entry locks for DAX? Is this > an issue currently, or are you just trying to make the code consistent so we > don't run into issues in the future? So dax_iomap_actor() copies data from / to user provided buffer. That can fault and if the buffer happens to be mmaped file on DAX filesystem, the fault will end up grabbing entry locks. Sample evil test: fd = open("some_file", O_RDWR); buf = mmap(NULL, 65536, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); write(fd, buf, 4096); Honza -- Jan Kara SUSE Labs, CR -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org