From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Mon, 9 Oct 2006 20:50:30 -0700 From: Andrew Morton Subject: Re: [patch] mm: bug in set_page_dirty_buffers Message-Id: <20061009205030.e247482e.akpm@osdl.org> In-Reply-To: <20061010033412.GH15822@wotan.suse.de> References: <20061010023654.GD15822@wotan.suse.de> <20061009202039.b6948a93.akpm@osdl.org> <20061010033412.GH15822@wotan.suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Nick Piggin Cc: Linus Torvalds , Peter Zijlstra , Linux Memory Management List , Greg KH List-ID: On Tue, 10 Oct 2006 05:34:12 +0200 Nick Piggin wrote: > On Mon, Oct 09, 2006 at 08:20:39PM -0700, Andrew Morton wrote: > > On Mon, 9 Oct 2006 20:06:05 -0700 (PDT) > > Linus Torvalds wrote: > > > > > On Tue, 10 Oct 2006, Nick Piggin wrote: > > > > > > > > This was triggered, but not the fault of, the dirty page accounting > > > > patches. Suitable for -stable as well, after it goes upstream. > > > > > > Applied. However, I wonder what protects "page_mapping()" here? > > > > Nothing. And I don't understand the (unchangelogged) switch from > > page->mapping to page_mapping(). > > I did the switch because that is that its callers and > the other spd functions are using to find the mapping. Maybe they're wrong? > > > I don't > > > think we hold the page lock anywhere, so "page->mapping" can change at any > > > time, no? > > > > Yes. The patch makes the race window a bit smaller. > > It fixes the problem. The mapping is already pinned at this point, Needs comment. > the problem is that page_mapping is still free to go NULL at any > time, and __set_page_dirty_buffers wasn't checking for that. > > If there is another race, then it must be because the buffer code > cannot cope with dirty buffers against a truncated page. It is > kind of spaghetti, though. What stops set_page_dirty_buffers from > racing with block_invalidatepage, for example? Nothing that I can think of. We keep on adding calls to set_page_dirty() against unlocked pages. It would have been better to fix that one case in the pte-unmapping path rather than adding heaps more. -- 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