From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752540Ab1HHNkl (ORCPT ); Mon, 8 Aug 2011 09:40:41 -0400 Received: from arkanian.console-pimps.org ([212.110.184.194]:34339 "EHLO arkanian.console-pimps.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751662Ab1HHNkk (ORCPT ); Mon, 8 Aug 2011 09:40:40 -0400 Subject: Re: [PATCH] x86, efi: Don't recursively acquire rtc_lock From: Matt Fleming To: Jan Beulich Cc: hpa@linux.intel.com, mjg@redhat.com, linux-kernel@vger.kernel.org, john stultz , Thomas Gleixner , Ingo Molnar , Marcelo Tosatti , Avi Kivity , Jeremy Fitzhardinge In-Reply-To: <4E3C30C602000078000740D5@nat28.tlf.novell.com> References: <4E3C30C602000078000740D5@nat28.tlf.novell.com> Content-Type: text/plain; charset="UTF-8" Date: Mon, 08 Aug 2011 14:40:36 +0100 Message-ID: <1312810836.10579.127.camel@mfleming-mobl1.ger.corp.intel.com> Mime-Version: 1.0 X-Mailer: Evolution 2.32.2 (2.32.2-1.fc14) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- arch/x86/kernel/rtc.c | 23 ++++++++++++----------- arch/x86/platform/mrst/vrtc.c | 9 +++++++++ 2 files changed, 21 insertions(+), 11 deletions(-) diff --git a/arch/x86/kernel/rtc.c b/arch/x86/kernel/rtc.c index 3f2ad26..ccdbc16 100644 --- a/arch/x86/kernel/rtc.c +++ b/arch/x86/kernel/rtc.c @@ -42,8 +42,11 @@ int mach_set_rtc_mmss(unsigned long nowtime) { int real_seconds, real_minutes, cmos_minutes; unsigned char save_control, save_freq_select; + unsigned long flags; int retval = 0; + spin_lock_irqsave(&rtc_lock, flags); + /* tell the clock it's being set */ save_control = CMOS_READ(RTC_CONTROL); CMOS_WRITE((save_control|RTC_SET), RTC_CONTROL); @@ -93,12 +96,17 @@ int mach_set_rtc_mmss(unsigned long nowtime) CMOS_WRITE(save_control, RTC_CONTROL); CMOS_WRITE(save_freq_select, RTC_FREQ_SELECT); + spin_unlock_irqrestore(&rtc_lock, flags); + return retval; } unsigned long mach_get_cmos_time(void) { unsigned int status, year, mon, day, hour, min, sec, century = 0; + unsigned long flags; + + spin_lock_irqsave(&rtc_lock, flags); /* * If UIP is clear, then we have >= 244 microseconds before @@ -125,6 +133,8 @@ unsigned long mach_get_cmos_time(void) status = CMOS_READ(RTC_CONTROL); WARN_ON_ONCE(RTC_ALWAYS_BCD && (status & RTC_DM_BINARY)); + spin_unlock_irqrestore(&rtc_lock, flags); + if (RTC_ALWAYS_BCD || !(status & RTC_DM_BINARY)) { sec = bcd2bin(sec); min = bcd2bin(min); @@ -169,24 +179,15 @@ EXPORT_SYMBOL(rtc_cmos_write); int update_persistent_clock(struct timespec now) { - unsigned long flags; - int retval; - - spin_lock_irqsave(&rtc_lock, flags); - retval = x86_platform.set_wallclock(now.tv_sec); - spin_unlock_irqrestore(&rtc_lock, flags); - - return retval; + return x86_platform.set_wallclock(now.tv_sec); } /* not static: needed by APM */ void read_persistent_clock(struct timespec *ts) { - unsigned long retval, flags; + unsigned long retval; - spin_lock_irqsave(&rtc_lock, flags); retval = x86_platform.get_wallclock(); - spin_unlock_irqrestore(&rtc_lock, flags); ts->tv_sec = retval; ts->tv_nsec = 0; diff --git a/arch/x86/platform/mrst/vrtc.c b/arch/x86/platform/mrst/vrtc.c index 73d70d6..6d5dbcd 100644 --- a/arch/x86/platform/mrst/vrtc.c +++ b/arch/x86/platform/mrst/vrtc.c @@ -58,8 +58,11 @@ EXPORT_SYMBOL_GPL(vrtc_cmos_write); unsigned long vrtc_get_time(void) { u8 sec, min, hour, mday, mon; + unsigned long flags; u32 year; + spin_lock_irqsave(&rtc_lock, flags); + while ((vrtc_cmos_read(RTC_FREQ_SELECT) & RTC_UIP)) cpu_relax(); @@ -70,6 +73,8 @@ unsigned long vrtc_get_time(void) mon = vrtc_cmos_read(RTC_MONTH); year = vrtc_cmos_read(RTC_YEAR); + spin_unlock_irqrestore(&rtc_lock, flags); + /* vRTC YEAR reg contains the offset to 1960 */ year += 1960; @@ -83,8 +88,10 @@ unsigned long vrtc_get_time(void) int vrtc_set_mmss(unsigned long nowtime) { int real_sec, real_min; + unsigned long flags; int vrtc_min; + spin_lock_irqsave(&rtc_lock, flags); vrtc_min = vrtc_cmos_read(RTC_MINUTES); real_sec = nowtime % 60; @@ -95,6 +102,8 @@ int vrtc_set_mmss(unsigned long nowtime) vrtc_cmos_write(real_sec, RTC_SECONDS); vrtc_cmos_write(real_min, RTC_MINUTES); + spin_unlock_irqrestore(&rtc_lock, flags); + return 0; } -- 1.7.4.4