From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail203.messagelabs.com (mail203.messagelabs.com [216.82.254.243]) by kanga.kvack.org (Postfix) with ESMTP id A070E6B0092 for ; Mon, 24 Jan 2011 14:48:16 -0500 (EST) In-reply-to: (message from Hugh Dickins on Fri, 21 Jan 2011 20:46:00 -0800 (PST)) Subject: Re: [PATCH] mm: prevent concurrent unmap_mapping_range() on the same inode References: <20110120124043.GA4347@infradead.org> Message-Id: From: Miklos Szeredi Date: Mon, 24 Jan 2011 20:47:44 +0100 Sender: owner-linux-mm@kvack.org To: Hugh Dickins Cc: miklos@szeredi.hu, hch@infradead.org, akpm@linux-foundation.org, gurudas.pai@oracle.com, lkml20101129@newton.leun.net, linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: On Fri, 21 Jan 2011, Hugh Dickins wrote: > 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. lookup_one_len lookup_hash __lookup_hash do_revalidate d_revalidate I don't see an easy way to get rid of i_mutex for lookup_one_len() and lookup_hash(). > 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. Yeah, fuse could use i_alloc_sem or a private mutex, but that would leave the other uses of unmap_mapping_range() to sort this out for themsevels. Thanks, Miklos -- 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/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: email@kvack.org