Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757854AbYAVWy4 (ORCPT ); Tue, 22 Jan 2008 17:54:56 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754744AbYAVWyq (ORCPT ); Tue, 22 Jan 2008 17:54:46 -0500 Received: from einhorn.in-berlin.de ([192.109.42.8]:34192 "EHLO einhorn.in-berlin.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753704AbYAVWyp (ORCPT ); Tue, 22 Jan 2008 17:54:45 -0500 X-Envelope-From: stefanr@s5r6.in-berlin.de Date: Tue, 22 Jan 2008 23:54:24 +0100 (CET) From: Stefan Richter Subject: [PATCH] lockdep: annotate epoll To: Peter Zijlstra cc: Denys Fedoryshchenko , linux-kernel@vger.kernel.org, Andrew Morton , Davide Libenzi In-Reply-To: Message-ID: References: <20080121160255.M12670@visp.net.lb> <47952094.9050102@s5r6.in-berlin.de> <20080122110448.M46928@visp.net.lb> <4796189F.8070506@s5r6.in-berlin.de> <1201019283.6341.28.camel@lappy> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; CHARSET=us-ascii Content-Disposition: INLINE Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3870 Lines: 106 On 22 Jan, Stefan Richter wrote: > On 22 Jan, Peter Zijlstra wrote: >> Curious though that this gets reported frequently the last few weeks, >> afaics this problem is way old. > > Here is a report against Fedora's 2.6.23-0.222.rc9.git4.fc8, filed in > October: https://bugzilla.redhat.com/show_bug.cgi?id=323411 Upstream bug: http://bugzilla.kernel.org/show_bug.cgi?id=9786 Date: Sun, 13 Jan 2008 19:44:26 +0100 From: Peter Zijlstra On Sat, 2008-01-05 at 13:35 -0800, Davide Libenzi wrote: > I remember I talked with Arjan about this time ago. Basically, since 1) > you can drop an epoll fd inside another epoll fd 2) callback-based wakeups > are used, you can see a wake_up() from inside another wake_up(), but they > will never refer to the same lock instance. > Think about: > > dfd = socket(...); > efd1 = epoll_create(); > efd2 = epoll_create(); > epoll_ctl(efd1, EPOLL_CTL_ADD, dfd, ...); > epoll_ctl(efd2, EPOLL_CTL_ADD, efd1, ...); > > When a packet arrives to the device underneath "dfd", the net code will > issue a wake_up() on its poll wake list. Epoll (efd1) has installed a > callback wakeup entry on that queue, and the wake_up() performed by the > "dfd" net code will end up in ep_poll_callback(). At this point epoll > (efd1) notices that it may have some event ready, so it needs to wake up > the waiters on its poll wait list (efd2). So it calls ep_poll_safewake() > that ends up in another wake_up(), after having checked about the > recursion constraints. That are, no more than EP_MAX_POLLWAKE_NESTS, to > avoid stack blasting. Never hit the same queue, to avoid loops like: > > epoll_ctl(efd2, EPOLL_CTL_ADD, efd1, ...); > epoll_ctl(efd3, EPOLL_CTL_ADD, efd2, ...); > epoll_ctl(efd4, EPOLL_CTL_ADD, efd3, ...); > epoll_ctl(efd1, EPOLL_CTL_ADD, efd4, ...); > > The code "if (tncur->wq == wq || ..." prevents re-entering the same > queue/lock. Since the epoll code is very careful to not nest same instance locks allow the recursion. Signed-off-by: Peter Zijlstra Tested-by: Stefan Richter --- fs/eventpoll.c | 2 +- include/linux/wait.h | 16 ++++++++++++++++ 2 files changed, 17 insertions(+), 1 deletion(-) Index: linux/fs/eventpoll.c =================================================================== --- linux.orig/fs/eventpoll.c +++ linux/fs/eventpoll.c @@ -353,7 +353,7 @@ static void ep_poll_safewake(struct poll spin_unlock_irqrestore(&psw->lock, flags); /* Do really wake up now */ - wake_up(wq); + wake_up_nested(wq, 1 + wake_nests); /* Remove the current task from the list */ spin_lock_irqsave(&psw->lock, flags); Index: linux/include/linux/wait.h =================================================================== --- linux.orig/include/linux/wait.h +++ linux/include/linux/wait.h @@ -161,6 +161,22 @@ wait_queue_head_t *FASTCALL(bit_waitqueu #define wake_up_locked(x) __wake_up_locked((x), TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE) #define wake_up_interruptible_sync(x) __wake_up_sync((x),TASK_INTERRUPTIBLE, 1) +#ifdef CONFIG_DEBUG_LOCK_ALLOC +/* + * macro to avoid include hell + */ +#define wake_up_nested(x, s) \ +do { \ + unsigned long flags; \ + \ + spin_lock_irqsave_nested(&(x)->lock, flags, (s)); \ + wake_up_locked(x); \ + spin_unlock_irqrestore(&(x)->lock, flags); \ +} while (0) +#else +#define wake_up_nested(x, s) wake_up(x) +#endif + #define __wait_event(wq, condition) \ do { \ DEFINE_WAIT(__wait); \ -- Stefan Richter -=====-==--- ---= =-==- http://arcgraph.de/sr/ -- 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/