From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cuda.sgi.com (cuda2.sgi.com [192.48.176.25]) by oss.sgi.com (8.14.3/8.14.3/SuSE Linux 0.8) with ESMTP id q4IDXCx7174329 for ; Fri, 18 May 2012 08:33:12 -0500 Received: from mx2.suse.de (cantor2.suse.de [195.135.220.15]) by cuda.sgi.com with ESMTP id 7RteIcyLacyKAM2s (version=TLSv1 cipher=AES256-SHA bits=256 verify=NO) for ; Fri, 18 May 2012 06:33:11 -0700 (PDT) Date: Fri, 18 May 2012 15:32:50 +0200 From: Jan Kara Subject: Re: Hole punching and mmap races Message-ID: <20120518133250.GC5589@quack.suse.cz> References: <20120515224805.GA25577@quack.suse.cz> <20120516021423.GO25351@dastard> <20120516130445.GA27661@quack.suse.cz> <20120517074308.GQ25351@dastard> <20120517232829.GA31028@quack.suse.cz> <20120518101210.GX25351@dastard> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20120518101210.GX25351@dastard> List-Id: XFS Filesystem from SGI List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: xfs-bounces@oss.sgi.com Errors-To: xfs-bounces@oss.sgi.com To: Dave Chinner Cc: Jan Kara , Hugh Dickins , xfs@oss.sgi.com, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org On Fri 18-05-12 20:12:10, Dave Chinner wrote: > On Fri, May 18, 2012 at 01:28:29AM +0200, Jan Kara wrote: > > On Thu 17-05-12 17:43:08, Dave Chinner wrote: > > > On Wed, May 16, 2012 at 03:04:45PM +0200, Jan Kara wrote: > > > > On Wed 16-05-12 12:14:23, Dave Chinner wrote: > > > IIRC, it's a rare case (that I consider insane, BTW): read from a > > > file with into a buffer that is a mmap()d region of the same file > > > that has not been faulted in yet..... > > With punch hole, the race is less insane - just punching hole in the area > > which is accessed via mmap could race in a bad way AFAICS. > > Seems the simple answer to me is to prevent page faults while hole > punching, then.... Yes, that's what I was suggesting in the beginning :) And I was asking whether people are OK with another lock in the page fault path (in particular in ->page_mkwrite) or whether someone has a better idea (e.g. taking mmap_sem in the hole punching path seems possible but I'm not sure whether that would be considered acceptable abuse). Honza -- Jan Kara SUSE Labs, CR _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs