From: Jiri Bohac <jbohac@suse.cz>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: jbohac@suse.cz, Andi Kleen <ak@suse.de>,
linux-kernel@vger.kernel.org, Vojtech Pavlik <vojtech@suse.cz>,
ssouhlal@freebsd.org, arjan@infradead.org, tglx@linutronix.de,
johnstul@us.ibm.com, zippel@linux-m68k.org, andrea@suse.de
Subject: Re: [patch 1/9] Fix HPET init race
Date: Tue, 6 Feb 2007 17:44:59 +0100 [thread overview]
Message-ID: <20070206164459.GA7271@dwarf.suse.cz> (raw)
In-Reply-To: <20070201183450.6d37d443.akpm@osdl.org>
On Thu, Feb 01, 2007 at 06:34:50PM -0800, Andrew Morton wrote:
> On Thu, 01 Feb 2007 10:59:53 +0100 jbohac@suse.cz wrote:
>
> > Fix a race in the initialization of HPET, which might result in a
> > 5 minute lockup on boot.
> >
>
> What race? Please always describe bugs when fixing them.
If the value of the HPET_T0_CMP register is reached and exceeded
by the value of the HPET_COUNTER register after HPET_T0_CMP is
read into trigger, but before the first iteration of the while,
the while loop will iterate "endlessly" until the HPET overlaps
eventually (in as much as 5 minutes).
> >
> > Index: linux-2.6.20-rc5/arch/x86_64/kernel/apic.c
> > ===================================================================
> > --- linux-2.6.20-rc5.orig/arch/x86_64/kernel/apic.c
> > +++ linux-2.6.20-rc5/arch/x86_64/kernel/apic.c
> > @@ -764,10 +767,12 @@ static void setup_APIC_timer(unsigned in
> >
> > /* wait for irq slice */
> > if (vxtime.hpet_address && hpet_use_timer) {
> > - int trigger = hpet_readl(HPET_T0_CMP);
> > - while (hpet_readl(HPET_COUNTER) >= trigger)
> > - /* do nothing */ ;
> > - while (hpet_readl(HPET_COUNTER) < trigger)
> > + int trigger;
> > + do
> > + trigger = hpet_readl(HPET_T0_CMP);
> > + while (hpet_readl(HPET_COUNTER) >= trigger);
> > +
>
> Is this signedness-safe and wraparound-safe? It might be better to make
> `trigger' unsigned and do
>
> while (hpet_readl(HPET_COUNTER) - trigger >= 0)
Yes, making trigger unsigned is a good idea (although having it
signed would probably never cause any problem, because this is
called during boot and it takes ~2 minutes for HPET to overflow
the s32)
But no, looping while the unsigned result is >= 0 does not seem
that good an idea to me ;-)
An updated patch follows. It is still not wraparound safe (a
lockup would still happen if it's called ~5 minutes after boot, but
this should never happen -- it's called early during boot)
--- linux-2.6.20-rc5.orig/arch/x86_64/kernel/apic.c 2007-02-06 16:56:00.000000000 +0100
+++ linux-2.6.20-rc5/arch/x86_64/kernel/apic.c 2007-02-06 17:26:42.000000000 +0100
@@ -764,10 +764,12 @@ static void setup_APIC_timer(unsigned in
/* wait for irq slice */
if (vxtime.hpet_address && hpet_use_timer) {
- int trigger = hpet_readl(HPET_T0_CMP);
- while (hpet_readl(HPET_COUNTER) >= trigger)
- /* do nothing */ ;
- while (hpet_readl(HPET_COUNTER) < trigger)
+ u32 trigger;
+ do
+ trigger = hpet_readl(HPET_T0_CMP);
+ while (hpet_readl(HPET_COUNTER) >= trigger);
+
+ while (hpet_readl(HPET_COUNTER) < trigger)
/* do nothing */ ;
} else {
int c1, c2;
--
Jiri Bohac <jbohac@suse.cz>
SUSE Labs, SUSE CZ
next prev parent reply other threads:[~2007-02-06 16:41 UTC|newest]
Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-02-01 9:59 [patch 0/9] x86_64: reliable TSC-based gettimeofday jbohac
2007-02-01 9:59 ` [patch 1/9] Fix HPET init race jbohac
2007-02-02 2:34 ` Andrew Morton
2007-02-06 16:44 ` Jiri Bohac [this message]
2007-02-07 0:12 ` Andrew Morton
2007-02-10 12:31 ` Andi Kleen
2007-07-26 20:58 ` Robin Holt
2007-02-01 9:59 ` [patch 2/9] Remove the support for the VXTIME_PMTMR timer mode jbohac
2007-02-01 11:13 ` Andi Kleen
2007-02-01 13:13 ` Jiri Bohac
2007-02-01 13:13 ` Andi Kleen
2007-02-01 13:59 ` Jiri Bohac
2007-02-01 14:18 ` Andi Kleen
2007-02-01 9:59 ` [patch 3/9] Remove the support for the VXTIME_HPET " jbohac
2007-02-01 9:59 ` [patch 4/9] Remove the TSC synchronization on SMP machines jbohac
2007-02-01 11:14 ` Andi Kleen
2007-02-01 13:17 ` Jiri Bohac
2007-02-01 15:16 ` Vojtech Pavlik
2007-02-02 7:14 ` Andi Kleen
2007-02-13 0:34 ` Christoph Lameter
2007-02-13 6:40 ` Arjan van de Ven
2007-02-13 8:28 ` Andi Kleen
2007-02-13 8:41 ` Arjan van de Ven
2007-02-13 17:09 ` Christoph Lameter
2007-02-13 17:20 ` Andi Kleen
2007-02-13 22:18 ` Vojtech Pavlik
2007-02-13 22:38 ` Andrea Arcangeli
2007-02-14 6:59 ` Vojtech Pavlik
2007-02-13 23:55 ` Christoph Lameter
2007-02-14 0:18 ` Paul Mackerras
2007-02-14 0:25 ` john stultz
2007-02-02 7:13 ` Andi Kleen
2007-02-01 21:05 ` mbligh
2007-02-03 1:16 ` H. Peter Anvin
2007-02-01 9:59 ` [patch 5/9] Add all the necessary structures to the vsyscall page jbohac
2007-02-01 11:17 ` Andi Kleen
2007-02-01 9:59 ` [patch 6/9] Add the "Master Timer" jbohac
2007-02-01 11:22 ` Andi Kleen
2007-02-01 13:29 ` Jiri Bohac
2007-02-01 9:59 ` [patch 7/9] Adapt the time initialization code jbohac
2007-02-01 11:26 ` Andi Kleen
2007-02-01 13:41 ` Jiri Bohac
2007-02-01 10:00 ` [patch 8/9] Add time_update_mt_guess() jbohac
2007-02-01 11:28 ` Andi Kleen
2007-02-01 13:54 ` Jiri Bohac
2007-02-01 10:00 ` [patch 9/9] Make use of the Master Timer jbohac
2007-02-01 11:36 ` Andi Kleen
2007-02-01 14:29 ` Jiri Bohac
2007-02-01 15:23 ` Vojtech Pavlik
2007-02-02 7:05 ` Andi Kleen
2007-02-02 7:04 ` Andi Kleen
2007-02-01 11:20 ` [patch 0/9] x86_64: reliable TSC-based gettimeofday Andi Kleen
2007-02-01 11:53 ` Andrea Arcangeli
2007-02-01 12:02 ` Andi Kleen
2007-02-01 12:54 ` Andrea Arcangeli
2007-02-01 12:17 ` Ingo Molnar
2007-02-01 14:52 ` Jiri Bohac
2007-02-01 16:56 ` john stultz
2007-02-01 19:41 ` Vojtech Pavlik
2007-02-01 11:34 ` Ingo Molnar
2007-02-01 11:46 ` [-mm patch] x86_64 GTOD: offer scalable vgettimeofday Ingo Molnar
2007-02-01 12:01 ` Andi Kleen
2007-02-01 12:14 ` Ingo Molnar
2007-02-01 12:17 ` [-mm patch] x86_64 GTOD: offer scalable vgettimeofday II Andi Kleen
2007-02-01 12:24 ` Ingo Molnar
2007-02-01 12:45 ` Andi Kleen
2007-02-02 4:22 ` [patch 0/9] x86_64: reliable TSC-based gettimeofday Andrew Morton
2007-02-02 7:07 ` Andi Kleen
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