Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Thu, 5 Sep 2002 03:22:09 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Thu, 5 Sep 2002 03:22:09 -0400 Received: from dsl-213-023-038-092.arcor-ip.net ([213.23.38.92]:45989 "EHLO starship") by vger.kernel.org with ESMTP id ; Thu, 5 Sep 2002 03:22:08 -0400 Content-Type: text/plain; charset=US-ASCII From: Daniel Phillips To: Andrew Morton Subject: Re: Race in shrink_cache Date: Thu, 5 Sep 2002 09:28:48 +0200 X-Mailer: KMail [version 1.3.2] Cc: linux-kernel@vger.kernel.org References:

<3D7702BE.85A5D11D@zip.com.au> In-Reply-To: <3D7702BE.85A5D11D@zip.com.au> MIME-Version: 1.0 Content-Transfer-Encoding: 7BIT Message-Id: Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1777 Lines: 49 On Thursday 05 September 2002 09:07, Andrew Morton wrote: > Daniel Phillips wrote: > > > > ... > > /* > > * We must not allow an anon page > > * with no buffers to be visible on > > * the LRU, so we unlock the page after > > * taking the lru lock > > */ > > > > That is, what's scary about an anon page without buffers? > > ooop. That's an akpm comment. umm, err.. > > It solves this BUG: > > http://www.cs.helsinki.fi/linux/linux-kernel/2001-37/0594.html > > Around the 2.4.10 timeframe, Andrea started putting anon pages > on the LRU. Then he backed that out, then put it in again. I > think this comment dates from the time when anon pages were > not on the LRU. So there's a little window there where the > page is unlocked, we've just dropped its swapdev buffers, the page is > on the LRU and pagemap_lru_lock is not held. > > So another CPU came in, found the page on the LRU, saw that it had > no ->mapping and no ->buffers and went BUG. > > The fix was to take pagemap_lru_lock before unlocking the page. > > The comment is stale. With the atomic_dec_and_lock strategy, the page would be freed immediately on the buffers being released, and with the lru=1 strategy it doesn't matter in terms of correctness whether the page ends up on the lru or not, so I was inclined not to worry about this anyway, still, when you a dire-looking comment like that... You said something about your lru locking strategy in 2.5.33-mm2. I have not reverse engineered it yet, would you care to wax poetic? -- Daniel - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/