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 C783F8D003A for ; Thu, 20 Jan 2011 09:14:45 -0500 (EST) In-reply-to: <20110120124043.GA4347@infradead.org> (message from Christoph Hellwig on Thu, 20 Jan 2011 07:40:43 -0500) Subject: Re: [PATCH] mm: prevent concurrent unmap_mapping_range() on the same inode References: <20110120124043.GA4347@infradead.org> Message-Id: From: Miklos Szeredi Date: Thu, 20 Jan 2011 15:13:59 +0100 Sender: owner-linux-mm@kvack.org To: Christoph Hellwig Cc: miklos@szeredi.hu, akpm@linux-foundation.org, hughd@google.com, gurudas.pai@oracle.com, lkml20101129@newton.leun.net, linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: On Thu, 20 Jan 2011, Christoph Hellwig wrote: > On Thu, Jan 20, 2011 at 01:30:58PM +0100, Miklos Szeredi wrote: > > From: Miklos Szeredi > > > > Running a fuse filesystem with multiple open()'s in parallel can > > trigger a "kernel BUG at mm/truncate.c:475" > > > > The reason is, unmap_mapping_range() is not prepared for more than > > one concurrent invocation per inode. For example: > > > > thread1: going through a big range, stops in the middle of a vma and > > stores the restart address in vm_truncate_count. > > > > thread2: comes in with a small (e.g. single page) unmap request on > > the same vma, somewhere before restart_address, finds that the > > vma was already unmapped up to the restart address and happily > > returns without doing anything. > > > > Another scenario would be two big unmap requests, both having to > > restart the unmapping and each one setting vm_truncate_count to its > > own value. This could go on forever without any of them being able to > > finish. > > > > 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. 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