From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with SMTP id C6EC36B004D for ; Wed, 18 Mar 2009 08:37:56 -0400 (EDT) From: Nick Piggin Subject: Re: fput under mmap_sem Date: Wed, 18 Mar 2009 23:37:48 +1100 References: <200903151459.01320.denys@visp.net.lb> <20090315221921.GY26138@disturbed> <20090318071313.GA30011@infradead.org> In-Reply-To: <20090318071313.GA30011@infradead.org> MIME-Version: 1.0 Content-Disposition: inline Message-Id: <200903182337.48789.nickpiggin@yahoo.com.au> Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Christoph Hellwig Cc: xfs@oss.sgi.com, linux-mm@kvack.org List-ID: On Wednesday 18 March 2009 18:13:13 Christoph Hellwig wrote: > On Mon, Mar 16, 2009 at 09:19:21AM +1100, Dave Chinner wrote: > > This is a VM problem where it calls fput() with the mmap_sem() held > > in remove_vma(). It makes the incorrect assumption that filesystems > > will never use the same lock in the IO path and the inode release path. > > > > This can deadlock if you are really unlucky. > > I really wonder why other filesystems haven't hit this yet. Any chance > we can get the fput moved out of mmap_sem to get rid of this class of > problems? Yes I don't think there is any reason against holding the file refcount a little longer, but it can be pretty nasty to do in practice because of deep call chains and sometimes multiple fputs within a given lock section. Possibly the easiest and quickest way will be to move aio's deferred __fput into a usable API and try that. If there are any performance problems, then we can try to move those fputs out from the mmap_sem one at a time (eg. I don't expect fput for vma replacement/merging to often cause the refcount to reach 0, and this is one of the harder places; wheras fput for a simple munmap might be more often causing refcount to reach 0 but it should be simpler to move out of mmap_sem if it is a problem). -- 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