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Message-ID: <47446690.5090808@redhat.com>
Date: Wed, 21 Nov 2007 12:10:40 -0500
From: Chuck Ebbert <cebbert@...hat.com>
To: Jordan Russell <jr-list-2007@....to>
CC: Andrew Morton <akpm@...ux-foundation.org>,
linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...e.hu>, john stultz <johnstul@...ibm.com>
Subject: Re: 2.6.23.1: Random hangs during boot with "tsc" clocksource
On 11/20/2007 06:20 PM, Jordan Russell wrote:
>>> On Fri, 02 Nov 2007 12:10:00 -0500 Jordan Russell <jr-list-2007@....to> wrote:
>>> Hi,
>>>
>>> With 2.6.23.1 (stock and Fedora), roughly 50% of the time my system
>>> hangs indefinitely during the kernel boot process. The hangs occur in
>>> places where normally a brief delay is seen, such as when detecting
>>> serial ports, ATA devices, and USB hubs. SysRq+W, when it works, shows
>>> tasks stuck inside schedule_timeout and lock_timer_base.
>
> Same problem with 2.6.23.8.
>
> Are there any specific (TSC related?) patches I should try reverting?
>
> Would it help if I captured the dmesg/SysRq output from one of the
> hanging boots?
>
> Any other information that might be useful in getting to the bottom of this?
>
Did you try this one? You are seeing problems with preemption disabled,
but it's at least worth trying.
From: Marin Mitov <mitov@...p.bas.bg>
To: linux-kernel@...r.kernel.org
Subject: [PATCH]new_TSC_based_delay_tsc()
Cc: Ingo Molnar <mingo@...e.hu>
Date: Tue, 20 Nov 2007 21:32:27 +0200
Hi all,
Please ignore the previous patch with the same subject.
It has a bug that can manifest itself in the very exotic case
when each do {} while() iteration executes on different cpu
leading to potentially infinite loop.
This is a patch based on the Ingo's idea/patch to track
delay_tsc() migration to another cpu by comparing
smp_processor_id(). It is against kernel-2.6.24-rc3.
What is different:
1. Using unsigned (instead of long) to unify for i386/x86_64.
2. Minimal preempt_disable/enable() critical sections
(more room for preemption)
3. some statements have been rearranged, to account for
possible under/overflow of left/TSC
Tested on both: 32/64 bit SMP PREEMPT kernel-2.6.24-rc3
Comments, please.
Signed-off-by: Marin Mitov <mitov@...p.bas.bg>
=========================================
--- a/arch/x86/lib/delay_32.c 2007-11-18 08:14:05.000000000 +0200
+++ b/arch/x86/lib/delay_32.c 2007-11-20 19:03:52.000000000 +0200
@@ -38,18 +38,42 @@
:"0" (loops));
}
-/* TSC based delay: */
+/* TSC based delay:
+ *
+ * We are careful about preemption as TSC's are per-CPU.
+ */
static void delay_tsc(unsigned long loops)
{
- unsigned long bclock, now;
+ unsigned prev, prev_1, now;
+ unsigned left = loops;
+ unsigned prev_cpu, cpu;
+
+ preempt_disable();
+ rdtscl(prev);
+ prev_cpu = smp_processor_id();
+ preempt_enable();
+ now = prev;
- preempt_disable(); /* TSC's are per-cpu */
- rdtscl(bclock);
do {
rep_nop();
+
+ left -= now - prev;
+ prev = now;
+
+ preempt_disable();
+ rdtscl(prev_1);
+ cpu = smp_processor_id();
rdtscl(now);
- } while ((now-bclock) < loops);
- preempt_enable();
+ preempt_enable();
+
+ if (prev_cpu != cpu){
+ /*
+ * We have migrated, forget prev_cpu's tsc reading
+ */
+ prev = prev_1;
+ prev_cpu = cpu;
+ }
+ } while ((now-prev) < left);
}
/*
--- a/arch/x86/lib/delay_64.c 2007-11-18 08:14:40.000000000 +0200
+++ b/arch/x86/lib/delay_64.c 2007-11-20 19:47:29.000000000 +0200
@@ -26,18 +26,42 @@
return 0;
}
+/* TSC based delay:
+ *
+ * We are careful about preemption as TSC's are per-CPU.
+ */
void __delay(unsigned long loops)
{
- unsigned bclock, now;
+ unsigned prev, prev_1, now;
+ unsigned left = loops;
+ unsigned prev_cpu, cpu;
+
+ preempt_disable();
+ rdtscl(prev);
+ prev_cpu = smp_processor_id();
+ preempt_enable();
+ now = prev;
- preempt_disable(); /* TSC's are pre-cpu */
- rdtscl(bclock);
do {
- rep_nop();
+ rep_nop();
+
+ left -= now - prev;
+ prev = now;
+
+ preempt_disable();
+ rdtscl(prev_1);
+ cpu = smp_processor_id();
rdtscl(now);
- }
- while ((now-bclock) < loops);
- preempt_enable();
+ preempt_enable();
+
+ if (prev_cpu != cpu){
+ /*
+ * We have migrated, forget prev_cpu's tsc reading
+ */
+ prev = prev_1;
+ prev_cpu = cpu;
+ }
+ } while ((now-prev) < left);
}
EXPORT_SYMBOL(__delay);
-
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