From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <447CE1A3.60507@yahoo.com.au> Date: Wed, 31 May 2006 10:21:55 +1000 From: Nick Piggin MIME-Version: 1.0 Subject: Re: [rfc][patch] remove racy sync_page? References: <447AC011.8050708@yahoo.com.au> <20060529121556.349863b8.akpm@osdl.org> <447B8CE6.5000208@yahoo.com.au> <20060529183201.0e8173bc.akpm@osdl.org> <447BB3FD.1070707@yahoo.com.au> <447BD31E.7000503@yahoo.com.au> <447BD9CE.2020505@yahoo.com.au> In-Reply-To: Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Hugh Dickins Cc: Linus Torvalds , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, mason@suse.com, andrea@suse.de, axboe@suse.de List-ID: Hugh Dickins wrote: > On Tue, 30 May 2006, Nick Piggin wrote: > >>But for 2.6.17, how's this? > > > It was a great emperor's-clothes-like discovery. But we've survived > for so many years without noticing, does it have to be fixed right > now for 2.6.17? (I bet I'd be insisting yes if I'd found it.) It's up to Linus and Andrew I guess. I don't see why not, but I don't much care one way or the other. But thanks having a quick look at it, we may want it for the Suse kernel. > > The thing I don't like about your lock_page_nosync (reasonable as > it is) is that the one case you're using it, set_page_dirty_nolock, > would be so much happier not to have to lock the page in the first > place - it's only doing _that_ to stabilize page->mapping, and the > lock_page forbids it from being called from anywhere that can't > sleep, which is often just where we want to call it from. Neil's > suggestion, using a spin_lock against the mapping changing, would > help there; but seems like more work than I'd want to get into. But making PG_lock a spinning lock is completely unrelated to the bug at hand. > > So, although I think lock_page_nosync fixes the bug (at least in > that one place we've identified there's likely to be such a bug), > it seems to be aiming at the wrong target. I'm pacing and thinking, > doubt I'll come up with anything better, please don't hold breath. It is the correct target. I know all about your set_page_dirty_lock problems, but they aren't what I'm trying to fix. AFAIKS, you could also make set_page_dirty_lock non sleeping quite easily by making inode slabs RCU freed. What places want to use set_page_dirty_lock without sleeping? The only place in drivers/ apart from sg/st that SetPageDirty are rd.c and via_dmablit.c, both of which look OK, if a bit crufty. -- SUSE Labs, Novell Inc. Send instant messages to your online friends http://au.messenger.yahoo.com -- 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