From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753267Ab1AVEqT (ORCPT ); Fri, 21 Jan 2011 23:46:19 -0500 Received: from smtp-out.google.com ([74.125.121.67]:39183 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751683Ab1AVEqS (ORCPT ); Fri, 21 Jan 2011 23:46:18 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=google.com; s=beta; h=date:from:x-x-sender:to:cc:subject:in-reply-to:message-id :references:user-agent:mime-version:content-type; b=Bc6zOtw8rphEoLUcIv2nX0HoHsPzaTIJ1I9GUQnExQtWFo4/KrQrCw6z9ll4ZD5JGc h+6yTlYHE3Ko65elUhTA== Date: Fri, 21 Jan 2011 20:46:00 -0800 (PST) From: Hugh Dickins X-X-Sender: hugh@sister.anvils To: Miklos Szeredi cc: Christoph Hellwig , akpm@linux-foundation.org, gurudas.pai@oracle.com, lkml20101129@newton.leun.net, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH] mm: prevent concurrent unmap_mapping_range() on the same inode In-Reply-To: Message-ID: References: <20110120124043.GA4347@infradead.org> User-Agent: Alpine 2.00 (LSU 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 20 Jan 2011, Miklos Szeredi wrote: > On Thu, 20 Jan 2011, Christoph Hellwig wrote: > > On Thu, Jan 20, 2011 at 01:30:58PM +0100, Miklos Szeredi wrote: > > > > > > Truncate and hole punching already serialize with i_mutex. Other > > > callers of unmap_mapping_range() do not, and it's difficult to get > > > i_mutex protection for all callers. In particular ->d_revalidate(), > > > which calls invalidate_inode_pages2_range() in fuse, may be called > > > with or without i_mutex. > > > > > > Which I think is mostly a fuse problem. I really hate bloating the > > generic inode (into which the address_space is embedded) with another > > mutex for deficits in rather special case filesystems. > > As Hugh pointed out unmap_mapping_range() has grown a varied set of > callers, which are difficult to fix up wrt i_mutex. Fuse was just an > example. > > I don't like the bloat either, but this is the best I could come up > with for fixing this problem generally. If you have a better idea, > please share it. If we start from the point that this is mostly a fuse problem (I expect that a thorough audit will show up a few other filesystems too, but let's start from this point): you cite ->d_revalidate as a particular problem, but can we fix up its call sites so that it is always called either with, or much preferably without, i_mutex held? Though actually I couldn't find where ->d_revalidate() is called while holding i_mutex. Failing that, can fuse down_write i_alloc_sem before calling invalidate_inode_pages2(_range), to achieve the same exclusion? The setattr truncation path takes i_alloc_sem as well as i_mutex, though I'm not certain of its full coverage. I did already consider holding and dropping i_alloc_sem inside invalidate_inode_pages2_range(); but direct-io.c very much wants to take mmap_sem (when get_user_pages_fast goes slow) after taking i_alloc_sem, whereas fuse_direct_mmap() very much wants to call invalidate_inode_pages2() while mmap_sem is held. Hugh