From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754290Ab2DXOIf (ORCPT ); Tue, 24 Apr 2012 10:08:35 -0400 Received: from relay.parallels.com ([195.214.232.42]:41475 "EHLO relay.parallels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754071Ab2DXOIe (ORCPT ); Tue, 24 Apr 2012 10:08:34 -0400 Message-ID: <4F96B3DD.3070909@parallels.com> Date: Tue, 24 Apr 2012 18:08:29 +0400 From: Vladimir Davydov User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.3) Gecko/20120314 Thunderbird/10.0.3 MIME-Version: 1.0 To: Paul Gortmaker CC: Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Andy Lutomirski , Jan Beulich , "x86@kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] arch: x86: take precautions against spurious timer interrupts References: <1335183494-19645-1-git-send-email-vdavydov@parallels.com> <4F96B0EB.1010601@windriver.com> In-Reply-To: <4F96B0EB.1010601@windriver.com> Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/24/2012 05:55 PM, Paul Gortmaker wrote: > On 12-04-23 08:18 AM, Vladimir Davydov wrote: >> If hpet is enabled by hpet_late_init() - this usually occurs on systems >> with buggy BIOS, which does not report about hpet presence through ACPI, >> hpet_clockevent's event_handler can be left uninitialized by >> clockevents_register_device() because of hpet_clockevent low rating (by >> the time hpet_late_init() is called, high prio apic timers have already >> been setup). The event_handler is then initialized a bit later by the >> clocksource_done_booting() procedure. >> >> Normally, timer interrupts should not be delivered between these two >> calls, but if e.g. the kernel is booted using kexec, there might be some >> pending interrupts from the previous kernel's context, which can lead to >> a NULL pointer dereference. > Reading between the lines here, I'm guessing that this is specific > to the kexec use case, and never seen anywhere else? Yes, you're right. I've caught it several times while using kexec. > In which case, > it seems a shame to add another conditional to the main timer_interrupt > for an event that may only happen once at boot, and even then, only > in a corner use-case. Can you deal with the invalid state somewhere > in an _init section instead, perhaps even within CONFIG_KEXEC? Or > at least ensure a dummy no-op handler is attached early enough? > > Paul. > -- Agree. I can init hpet_clockevent.event_handler with clockevents_handle_noop() in its definition. Will rework and resend. Thanks for replying. > >> So, take precautions against spurious timer interrupts by checking the >> event_handler value before calling it. >> --- >> arch/x86/kernel/time.c | 18 +++++++++++++++++- >> 1 files changed, 17 insertions(+), 1 deletions(-) >> >> diff --git a/arch/x86/kernel/time.c b/arch/x86/kernel/time.c >> index c6eba2b..43bdd3a 100644 >> --- a/arch/x86/kernel/time.c >> +++ b/arch/x86/kernel/time.c >> @@ -57,7 +57,23 @@ EXPORT_SYMBOL(profile_pc); >> */ >> static irqreturn_t timer_interrupt(int irq, void *dev_id) >> { >> - global_clock_event->event_handler(global_clock_event); >> + /* >> + * If hpet is enabled by hpet_late_init(), event_handler can be left >> + * uninitialized by clockevents_register_device() because of >> + * hpet_clockevent low rating (by the time hpet_late_init() is called, >> + * high prio apic timers have already been setup). The event_handler is >> + * then initialized a bit later by the clocksource_done_booting() >> + * procedure. >> + * >> + * Normally, timer interrupts should not be delivered between these two >> + * calls, but if e.g. the kernel is booted using kexec, there might be >> + * some pending interrupts from the previous kernel's context, which >> + * can lead to a NULL pointer dereference. >> + * >> + * So, take precautions against spurious timer interrupts. >> + */ >> + if (global_clock_event->event_handler) >> + global_clock_event->event_handler(global_clock_event); >> >> /* MCA bus quirk: Acknowledge irq0 by setting bit 7 in port 0x61 */ >> if (MCA_bus)