Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755857AbXJ0PvV (ORCPT ); Sat, 27 Oct 2007 11:51:21 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752663AbXJ0PvN (ORCPT ); Sat, 27 Oct 2007 11:51:13 -0400 Received: from pentafluge.infradead.org ([213.146.154.40]:47885 "EHLO pentafluge.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752650AbXJ0PvN (ORCPT ); Sat, 27 Oct 2007 11:51:13 -0400 Date: Sat, 27 Oct 2007 08:47:13 -0700 From: Arjan van de Ven To: Jiri Kosina Cc: Gabriel C , a.zummo@towertech.it, Linux Kernel Mailing List , Andrew Morton , rtc-linux@googlegroups.com, Peter Zijlstra Subject: Re: BUG: lock held when returning to user space Message-ID: <20071027084713.72733460@laptopd505.fenrus.org> In-Reply-To: References: <472348F6.6050100@googlemail.com> Organization: Intel X-Mailer: Claws Mail 3.0.2 (GTK+ 2.12.1; i386-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-SRS-Rewrite: SMTP reverse-path rewritten from by pentafluge.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1878 Lines: 45 On Sat, 27 Oct 2007 17:12:41 +0200 (CEST) Jiri Kosina wrote: > On Sat, 27 Oct 2007, Gabriel C wrote: > > > I found that today in dmesg after booting current git ( > > ec3b67c11df42362ccda81261d62829042f223f0 ) : > > ... > > [ 592.752777] > > [ 592.752781] ================================================ > > [ 592.753478] [ BUG: lock held when returning to user space! ] > > [ 592.753880] ------------------------------------------------ > > [ 592.754262] hwclock/1452 is leaving the kernel with locks still > > held! [ 592.754655] 1 lock held by hwclock/1452: > > [ 592.755007] #0: (&rtc->char_lock){--..}, at: [] > > rtc_dev_open+0x2e/0x7e > > Yes, this is because rtc keeps a char_lock mutex locked as long as > the device is open, to avoid concurrent accessess. > > It could be easily substituted by some counting -- setting and > clearing bit in struct rtc_device instead of using char_lock, but > doing this just to shut the lockdep off is questionable imho. it's not about lockdep; what this code doing is not valid use of a mutex: A mutex is required to have a clear process as owner, and in this case it doesn't have that... at all. This is a violation of the kernel mutex semantics.. and should be fixed. > Peter, what is the preferred way to annotate these kinds of locking > for lockdep to express that it is intended? the preferred method is to not use a mutex like this... -- If you want to reach me at my work email, use arjan@linux.intel.com For development, discussion and tips for power savings, visit http://www.lesswatts.org - 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/