From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752379Ab1HJJEr (ORCPT ); Wed, 10 Aug 2011 05:04:47 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:59019 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751393Ab1HJJEp (ORCPT ); Wed, 10 Aug 2011 05:04:45 -0400 Date: Wed, 10 Aug 2011 11:03:30 +0200 From: Ingo Molnar To: Jan Beulich Cc: Matt Fleming , Jeremy Fitzhardinge , Thomas Gleixner , hpa@linux.intel.com, Avi Kivity , mjg@redhat.com, Marcelo Tosatti , johnstultz , linux-kernel@vger.kernel.org Subject: Re: [PATCH] x86, efi: Don't recursively acquire rtc_lock Message-ID: <20110810090330.GF26762@elte.hu> References: <4E3C30C602000078000740D5@nat28.tlf.novell.com> <1312810836.10579.127.camel@mfleming-mobl1.ger.corp.intel.com> <4E4009A50200007800050258@nat28.tlf.novell.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4E4009A50200007800050258@nat28.tlf.novell.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-ELTE-SpamScore: -1.9 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.9 required=5.9 tests=AWL,BAYES_00 autolearn=no SpamAssassin version=3.3.1 -2.0 BAYES_00 BODY: Bayes spam probability is 0 to 1% [score: 0.0000] 0.1 AWL AWL: From: address is in the auto white-list Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Jan Beulich wrote: > >>> On 08.08.11 at 15:40, Matt Fleming wrote: > > On Fri, 2011-08-05 at 18:04 +0100, Jan Beulich wrote: > >> > >> Virtual platforms will have to take care of the serialization in the > >> host anyway, so the guest side implementation of getwallclock et al > >> is entirely unaffected. > > > > Ah, OK, that's the important part. I didn't realise that rtc_lock isn't > > actually required by any other code. In which case, yes, it completely > > makes sense to push the locking of rtc_lock down into the > > implementations that actually need it. > > > > It'd be great if I could get some ACK's from the virtualization guys. > > > > --------8<-------- > > > > From a0a39dbb69f6ac675846bf00f30ad153506a4567 Mon Sep 17 00:00:00 2001 > > From: Matt Fleming > > Date: Mon, 8 Aug 2011 12:59:35 +0100 > > Subject: [PATCH] x86, efi: Don't recursively acquire rtc_lock > > > > A deadlock was introduced on x86 in commit ef68c8f87ed1 ("x86: > > Serialize EFI time accesses on rtc_lock") because efi_get_time() and > > friends can be called with rtc_lock already held by > > read_persistent_time(), e.g. > > > > timekeeping_init() > > read_persistent_clock() <-- acquire rtc_lock > > efi_get_time() > > phys_efi_get_time() <-- acquire rtc_lock > > > > To fix this let's push the locking down into the get_wallclock() and > > set_wallclock() implementations. Only the clock implementations that > > access the x86 RTC directly need to acquire rtc_lock, so it makes > > sense to push the locking down into the rtc, vrtc and efi code. > > > > The virtualization implementations don't require rtc_lock to be held > > because they provide their own serialization. > > > > Signed-off-by: Matt Fleming > > Acked-by: Jan Beulich How urgent is thix fix - can it wait until Thomas comes back and starts processing patches again? Thanks, Ingo