[PATCH] [BUGFIX] crash/ioapic: Prevent crash_kexec() from deadlocking of ioapic_lock

[PATCH] [BUGFIX] crash/ioapic: Prevent crash_kexec() from deadlocking of ioapic_lock

[Yoshihiro YUNOMAE]

Prevent crash_kexec() from deadlocking of ioapic_lock. When crash_kexec()
is executed on a cpu, the cpu will get ioapic_lock in disable_IO_APIC().
So if the cpu gets NMI while locking ioapic_lock, a deadlock wiil happen.
In this patch, ioapic_lock is initialized before disable_IO_APIC().

To confirm this deadlocking, you'll set up as follows:

1. Add mdelay(1000) after raw_spin_lock_irqsave() in
   native_ioapic_set_affinity()@arch/x86/kernel/apic/io_apic.c

   Although the deadlocking can occur without this modification, it will
  increase the potential of the deadlocking problem.

2. Build and install the kernel

3. Set up the OS which will run panic() and kexec when NMI is injected
    # echo "kernel.unknown_nmi_panic=1" >> /etc/sysctl.conf
    # vim /etc/default/grub
      add "nmi_watchdog=0 crashkernel=256M" in GRUB_CMDLINE_LINUX line
    # grub2-mkconfig

4. Reboot the OS

5. Run following command for each vcpu on the guest
    # while true; do echo <CPU num> > /proc/irq/<IO-APIC-edge or IO-APIC-fasteoi>/smp_affinitity; done;
   By running this command, cpus will get ioapic_lock for setting affinity.

6. Inject NMI (push a dump button or execute 'virsh inject-nmi <domain>' if you
   use VM)
   After injecting NMI, panic() is called in an nmi-handler context.
   Then, kexec will normally run in panic(), but the operation will be stopped
   by deadlock of ioapic_lock in crash_kexec()->machine_crash_shutdown()->
   native_machine_crash_shutdown()->disable_IO_APIC()->clear_IO_APIC()->
   clear_IO_APIC_pin()->ioapic_read_entry().

Signed-off-by: Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@hitachi.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Seiji Aguchi <seiji.aguchi@hds.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Gleb Natapov <gleb@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: linux-kernel@vger.kernel.org
Cc: stable@vger.kernel.org
---
 arch/x86/include/asm/apic.h    |    2 ++
 arch/x86/kernel/apic/io_apic.c |    5 +++++
 arch/x86/kernel/crash.c        |    4 ++++
 3 files changed, 11 insertions(+)

diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
index f8119b5..ddb06af 100644
--- a/arch/x86/include/asm/apic.h
+++ b/arch/x86/include/asm/apic.h
@@ -715,4 +715,6 @@ static inline void exiting_ack_irq(void)
 	ack_APIC_irq();
 }
 
+extern void ioapic_lock_init(void);
+
 #endif /* _ASM_X86_APIC_H */
diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
index 9ed796c..2816c07 100644
--- a/arch/x86/kernel/apic/io_apic.c
+++ b/arch/x86/kernel/apic/io_apic.c
@@ -1534,6 +1534,11 @@ void intel_ir_io_apic_print_entries(unsigned int apic,
 	}
 }
 
+void ioapic_lock_init(void)
+{
+	raw_spin_lock_init(&ioapic_lock);
+}
+
 __apicdebuginit(void) print_IO_APIC(int ioapic_idx)
 {
 	union IO_APIC_reg_00 reg_00;
diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index 74467fe..ea039d5 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -129,6 +129,10 @@ void native_machine_crash_shutdown(struct pt_regs *regs)
 
 	lapic_shutdown();
 #if defined(CONFIG_X86_IO_APIC)
+	/*
+	 * Prevent crash_kexec() from deadlocking of ioapic_lock.
+	 */
+	ioapic_lock_init();
 	disable_IO_APIC();
 #endif
 #ifdef CONFIG_HPET_TIMER

Re: [PATCH] [BUGFIX] crash/ioapic: Prevent crash_kexec() from deadlocking of ioapic_lock

[Ingo Molnar]

* Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@hitachi.com> wrote:

> Prevent crash_kexec() from deadlocking of ioapic_lock. 

s/of/on

> When crash_kexec() is executed on a cpu, the cpu will get 
> ioapic_lock in disable_IO_APIC(). So if the cpu gets NMI 
> while locking ioapic_lock, a deadlock wiil happen. In 

s/will

> this patch, ioapic_lock is initialized before 
> disable_IO_APIC().
> 
> To confirm this deadlocking, you'll set up as follows:

s/deadlocking/deadlock

> 1. Add mdelay(1000) after raw_spin_lock_irqsave() in
>    native_ioapic_set_affinity()@arch/x86/kernel/apic/io_apic.c
> 
>    Although the deadlocking can occur without this modification, it will
>   increase the potential of the deadlocking problem.

s/deadlocking/deadlock

> 
> 2. Build and install the kernel
> 
> 3. Set up the OS which will run panic() and kexec when NMI is injected
>     # echo "kernel.unknown_nmi_panic=1" >> /etc/sysctl.conf
>     # vim /etc/default/grub
>       add "nmi_watchdog=0 crashkernel=256M" in GRUB_CMDLINE_LINUX line
>     # grub2-mkconfig
> 
> 4. Reboot the OS
> 
> 5. Run following command for each vcpu on the guest
>     # while true; do echo <CPU num> > /proc/irq/<IO-APIC-edge or IO-APIC-fasteoi>/smp_affinitity; done;
>    By running this command, cpus will get ioapic_lock for setting affinity.
> 
> 6. Inject NMI (push a dump button or execute 'virsh inject-nmi <domain>' if you
>    use VM)
>    After injecting NMI, panic() is called in an nmi-handler context.
>    Then, kexec will normally run in panic(), but the operation will be stopped
>    by deadlock of ioapic_lock in crash_kexec()->machine_crash_shutdown()->

s/of/on

>    native_machine_crash_shutdown()->disable_IO_APIC()->clear_IO_APIC()->
>    clear_IO_APIC_pin()->ioapic_read_entry().

I suppose we could do this patch if it's a common 
occurance.

A few minor details need fixing:

> 
> Signed-off-by: Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@hitachi.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: x86@kernel.org
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Andi Kleen <ak@linux.intel.com>
> Cc: Seiji Aguchi <seiji.aguchi@hds.com>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> Cc: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
> Cc: Joerg Roedel <joro@8bytes.org>
> Cc: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
> Cc: "Eric W. Biederman" <ebiederm@xmission.com>
> Cc: Gleb Natapov <gleb@redhat.com>
> Cc: Marcelo Tosatti <mtosatti@redhat.com>
> Cc: linux-kernel@vger.kernel.org
> Cc: stable@vger.kernel.org
> ---
>  arch/x86/include/asm/apic.h    |    2 ++
>  arch/x86/kernel/apic/io_apic.c |    5 +++++
>  arch/x86/kernel/crash.c        |    4 ++++
>  3 files changed, 11 insertions(+)
> 
> diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
> index f8119b5..ddb06af 100644
> --- a/arch/x86/include/asm/apic.h
> +++ b/arch/x86/include/asm/apic.h
> @@ -715,4 +715,6 @@ static inline void exiting_ack_irq(void)
>  	ack_APIC_irq();
>  }
>  
> +extern void ioapic_lock_init(void);
> +
>  #endif /* _ASM_X86_APIC_H */
> diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
> index 9ed796c..2816c07 100644
> --- a/arch/x86/kernel/apic/io_apic.c
> +++ b/arch/x86/kernel/apic/io_apic.c
> @@ -1534,6 +1534,11 @@ void intel_ir_io_apic_print_entries(unsigned int apic,
>  	}
>  }
>  
> +void ioapic_lock_init(void)
> +{
> +	raw_spin_lock_init(&ioapic_lock);
> +}

Please name this ioapic_zap_locks() to make clear that this 
is crash handling related.

> +
>  __apicdebuginit(void) print_IO_APIC(int ioapic_idx)
>  {
>  	union IO_APIC_reg_00 reg_00;
> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
> index 74467fe..ea039d5 100644
> --- a/arch/x86/kernel/crash.c
> +++ b/arch/x86/kernel/crash.c
> @@ -129,6 +129,10 @@ void native_machine_crash_shutdown(struct pt_regs *regs)
>  
>  	lapic_shutdown();
>  #if defined(CONFIG_X86_IO_APIC)

Please enhance this #ifdef while at it.

> +	/*
> +	 * Prevent crash_kexec() from deadlocking of ioapic_lock.
> +	 */

s/of/on.

Also, single-line comment can go /* here */.

> +	ioapic_lock_init();
>  	disable_IO_APIC();
>  #endif
>  #ifdef CONFIG_HPET_TIMER
> 

Thanks,

	Ingo

Re: Re: [PATCH] [BUGFIX] crash/ioapic: Prevent crash_kexec() from deadlocking of ioapic_lock

[Yoshihiro YUNOMAE]

Hi Ingo,

Thank you for fixing typos!
OK, I'll fix them and rename to ioapic_zap_locks().

Thank you again!

Yoshihiro YUNOMAE

(2013/08/19 18:46), Ingo Molnar wrote:
>
> * Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@hitachi.com> wrote:
>
>> Prevent crash_kexec() from deadlocking of ioapic_lock.
>
> s/of/on
>
>> When crash_kexec() is executed on a cpu, the cpu will get
>> ioapic_lock in disable_IO_APIC(). So if the cpu gets NMI
>> while locking ioapic_lock, a deadlock wiil happen. In
>
> s/will
>
>> this patch, ioapic_lock is initialized before
>> disable_IO_APIC().
>>
>> To confirm this deadlocking, you'll set up as follows:
>
> s/deadlocking/deadlock
>
>> 1. Add mdelay(1000) after raw_spin_lock_irqsave() in
>>     native_ioapic_set_affinity()@arch/x86/kernel/apic/io_apic.c
>>
>>     Although the deadlocking can occur without this modification, it will
>>    increase the potential of the deadlocking problem.
>
> s/deadlocking/deadlock
>
>>
>> 2. Build and install the kernel
>>
>> 3. Set up the OS which will run panic() and kexec when NMI is injected
>>      # echo "kernel.unknown_nmi_panic=1" >> /etc/sysctl.conf
>>      # vim /etc/default/grub
>>        add "nmi_watchdog=0 crashkernel=256M" in GRUB_CMDLINE_LINUX line
>>      # grub2-mkconfig
>>
>> 4. Reboot the OS
>>
>> 5. Run following command for each vcpu on the guest
>>      # while true; do echo <CPU num> > /proc/irq/<IO-APIC-edge or IO-APIC-fasteoi>/smp_affinitity; done;
>>     By running this command, cpus will get ioapic_lock for setting affinity.
>>
>> 6. Inject NMI (push a dump button or execute 'virsh inject-nmi <domain>' if you
>>     use VM)
>>     After injecting NMI, panic() is called in an nmi-handler context.
>>     Then, kexec will normally run in panic(), but the operation will be stopped
>>     by deadlock of ioapic_lock in crash_kexec()->machine_crash_shutdown()->
>
> s/of/on
>
>>     native_machine_crash_shutdown()->disable_IO_APIC()->clear_IO_APIC()->
>>     clear_IO_APIC_pin()->ioapic_read_entry().
>
> I suppose we could do this patch if it's a common
> occurance.
>
> A few minor details need fixing:
>
>>
>> Signed-off-by: Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@hitachi.com>
>> Cc: Thomas Gleixner <tglx@linutronix.de>
>> Cc: Ingo Molnar <mingo@redhat.com>
>> Cc: "H. Peter Anvin" <hpa@zytor.com>
>> Cc: x86@kernel.org
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: Andi Kleen <ak@linux.intel.com>
>> Cc: Seiji Aguchi <seiji.aguchi@hds.com>
>> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
>> Cc: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
>> Cc: Joerg Roedel <joro@8bytes.org>
>> Cc: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
>> Cc: "Eric W. Biederman" <ebiederm@xmission.com>
>> Cc: Gleb Natapov <gleb@redhat.com>
>> Cc: Marcelo Tosatti <mtosatti@redhat.com>
>> Cc: linux-kernel@vger.kernel.org
>> Cc: stable@vger.kernel.org
>> ---
>>   arch/x86/include/asm/apic.h    |    2 ++
>>   arch/x86/kernel/apic/io_apic.c |    5 +++++
>>   arch/x86/kernel/crash.c        |    4 ++++
>>   3 files changed, 11 insertions(+)
>>
>> diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
>> index f8119b5..ddb06af 100644
>> --- a/arch/x86/include/asm/apic.h
>> +++ b/arch/x86/include/asm/apic.h
>> @@ -715,4 +715,6 @@ static inline void exiting_ack_irq(void)
>>   	ack_APIC_irq();
>>   }
>>
>> +extern void ioapic_lock_init(void);
>> +
>>   #endif /* _ASM_X86_APIC_H */
>> diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
>> index 9ed796c..2816c07 100644
>> --- a/arch/x86/kernel/apic/io_apic.c
>> +++ b/arch/x86/kernel/apic/io_apic.c
>> @@ -1534,6 +1534,11 @@ void intel_ir_io_apic_print_entries(unsigned int apic,
>>   	}
>>   }
>>
>> +void ioapic_lock_init(void)
>> +{
>> +	raw_spin_lock_init(&ioapic_lock);
>> +}
>
> Please name this ioapic_zap_locks() to make clear that this
> is crash handling related.
>
>> +
>>   __apicdebuginit(void) print_IO_APIC(int ioapic_idx)
>>   {
>>   	union IO_APIC_reg_00 reg_00;
>> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
>> index 74467fe..ea039d5 100644
>> --- a/arch/x86/kernel/crash.c
>> +++ b/arch/x86/kernel/crash.c
>> @@ -129,6 +129,10 @@ void native_machine_crash_shutdown(struct pt_regs *regs)
>>
>>   	lapic_shutdown();
>>   #if defined(CONFIG_X86_IO_APIC)
>
> Please enhance this #ifdef while at it.
>
>> +	/*
>> +	 * Prevent crash_kexec() from deadlocking of ioapic_lock.
>> +	 */
>
> s/of/on.
>
> Also, single-line comment can go /* here */.
>
>> +	ioapic_lock_init();
>>   	disable_IO_APIC();
>>   #endif
>>   #ifdef CONFIG_HPET_TIMER
>>
>
> Thanks,
>
> 	Ingo
> --
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> Please read the FAQ at  http://www.tux.org/lkml/
>

-- 
Yoshihiro YUNOMAE
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: yoshihiro.yunomae.ez@hitachi.com

Re: [PATCH] [BUGFIX] crash/ioapic: Prevent crash_kexec() from deadlocking of ioapic_lock

[Eric W. Biederman]

Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@hitachi.com> writes:

> Hi Ingo,
>
> Thank you for fixing typos!
> OK, I'll fix them and rename to ioapic_zap_locks().
>
> Thank you again!


The better fix for this would be to remove the disable_IO_APIC call from
crash_kexec.

I know last time it was investigated the kernel was very close to
working without needing that, and the code will be much more robust in
the long term if we can avoid disabling them in the crashing kernel.

Yoshihiro is there any chance you can look into removing the
disable_IO_APIC entirely?

The apic disablement and the disable_IO_APIC exists entirely due to
limitations in the kernel boot path.

Eric

Re: [PATCH] [BUGFIX] crash/ioapic: Prevent crash_kexec() from deadlocking of ioapic_lock

[Don Zickus]

On Tue, Aug 20, 2013 at 03:12:32AM -0700, Eric W. Biederman wrote:
> Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@hitachi.com> writes:
> 
> > Hi Ingo,
> >
> > Thank you for fixing typos!
> > OK, I'll fix them and rename to ioapic_zap_locks().
> >
> > Thank you again!
> 
> 
> The better fix for this would be to remove the disable_IO_APIC call from
> crash_kexec.
> 
> I know last time it was investigated the kernel was very close to
> working without needing that, and the code will be much more robust in
> the long term if we can avoid disabling them in the crashing kernel.
> 
> Yoshihiro is there any chance you can look into removing the
> disable_IO_APIC entirely?
> 
> The apic disablement and the disable_IO_APIC exists entirely due to
> limitations in the kernel boot path.

Yup.  We went down this path a year ago:

https://lkml.org/lkml/2012/2/2/331

Then we got sidetracked and talked about removing the lapic stuff at
shutdown too:

http://lists.infradead.org/pipermail/kexec/2012-February/006017.html
(sorry couldn't find lkml link for some reason)

And the second patch was committed.

However, it was quickly reverted when Yinghai Lu noticed a problem:

https://lkml.org/lkml/2012/2/11/143

The problem stemmed from the fact that the nmi_watchdog caused an NMI in
the middle of transitioning between the two kernels (we didn't shutdown
the lapic) and caused a reset (there is no NMI handler in purgatory).

I think I dropped the ball in investigating how to write an idt for the
purgatory code to handle spurious NMIs.

Regardless of all that, I think if we stick to just removing the ioapic
shutdown code (ie the first patch linked above), we should be ok.  I
believe my testing went smoothly.  It was the lapic stuff that needed more
tweaking.

So, I agree with Eric, let's remove the disable_IO_APIC() stuff and keep
the code simpler.

Cheers,
Don

Re: Re: [PATCH] [BUGFIX] crash/ioapic: Prevent crash_kexec() from deadlocking of ioapic_lock

[Yoshihiro YUNOMAE]

(2013/08/20 23:27), Don Zickus wrote:
> On Tue, Aug 20, 2013 at 03:12:32AM -0700, Eric W. Biederman wrote:
>> Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@hitachi.com> writes:
>>
>>> Hi Ingo,
>>>
>>> Thank you for fixing typos!
>>> OK, I'll fix them and rename to ioapic_zap_locks().
>>>
>>> Thank you again!
>>
>>
>> The better fix for this would be to remove the disable_IO_APIC call from
>> crash_kexec.
>>
>> I know last time it was investigated the kernel was very close to
>> working without needing that, and the code will be much more robust in
>> the long term if we can avoid disabling them in the crashing kernel.
>>
>> Yoshihiro is there any chance you can look into removing the
>> disable_IO_APIC entirely?
>>
>> The apic disablement and the disable_IO_APIC exists entirely due to
>> limitations in the kernel boot path.
>
> Yup.  We went down this path a year ago:
>
> https://lkml.org/lkml/2012/2/2/331
>
> Then we got sidetracked and talked about removing the lapic stuff at
> shutdown too:
>
> http://lists.infradead.org/pipermail/kexec/2012-February/006017.html
> (sorry couldn't find lkml link for some reason)
>
> And the second patch was committed.
>
> However, it was quickly reverted when Yinghai Lu noticed a problem:
>
> https://lkml.org/lkml/2012/2/11/143
>
> The problem stemmed from the fact that the nmi_watchdog caused an NMI in
> the middle of transitioning between the two kernels (we didn't shutdown
> the lapic) and caused a reset (there is no NMI handler in purgatory).
>
> I think I dropped the ball in investigating how to write an idt for the
> purgatory code to handle spurious NMIs.
>
> Regardless of all that, I think if we stick to just removing the ioapic
> shutdown code (ie the first patch linked above), we should be ok.  I
> believe my testing went smoothly.  It was the lapic stuff that needed more
> tweaking.
>
> So, I agree with Eric, let's remove the disable_IO_APIC() stuff and keep
> the code simpler.

Thank you for commenting about my patch.
I didn't know you already have submitted the patches for this deadlock
problem.

I can't answer definitively right now that no problems are induced by
removing disable_IO_APIC(). However, my patch should be work well (and
has already been merged to -tip tree). So how about taking my patch at
first, and then discussing the removal of disabled_IO_APIC()?

Thanks,
Yoshihiro YUNOMAE

-- 
Yoshihiro YUNOMAE
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: yoshihiro.yunomae.ez@hitachi.com

Re: Re: [PATCH] [BUGFIX] crash/ioapic: Prevent crash_kexec() from deadlocking of ioapic_lock

[Don Zickus]

On Thu, Aug 22, 2013 at 05:38:07PM +0900, Yoshihiro YUNOMAE wrote:
> >So, I agree with Eric, let's remove the disable_IO_APIC() stuff and keep
> >the code simpler.
> 
> Thank you for commenting about my patch.
> I didn't know you already have submitted the patches for this deadlock
> problem.
> 
> I can't answer definitively right now that no problems are induced by
> removing disable_IO_APIC(). However, my patch should be work well (and
> has already been merged to -tip tree). So how about taking my patch at
> first, and then discussing the removal of disabled_IO_APIC()?

It doesn't matter to me.  My orignal patch last year was similar to yours
until it was suggested that we were working around a problem which was we
shouldn't touch the IO_APIC code on panic.  Then I wrote the removal of
disable_IO_APIC patch and did lots of testing on it.  I don't think I have
seen any issues with it (just the removal of disabling the lapic stuff).

Regardless, your patch fixes a similar problem we saw on RHEL, so I am
happy either way.  The removal of the disable_IO_APIC() just makes the
code look cleaner.

Cheers,
Don

Re: Re: Re: [PATCH] [BUGFIX] crash/ioapic: Prevent crash_kexec() from deadlocking of ioapic_lock

[Yoshihiro YUNOMAE]

Hi Don,

Sorry for the late reply.

(2013/08/22 22:11), Don Zickus wrote:
> On Thu, Aug 22, 2013 at 05:38:07PM +0900, Yoshihiro YUNOMAE wrote:
>>> So, I agree with Eric, let's remove the disable_IO_APIC() stuff and keep
>>> the code simpler.
>>
>> Thank you for commenting about my patch.
>> I didn't know you already have submitted the patches for this deadlock
>> problem.
>>
>> I can't answer definitively right now that no problems are induced by
>> removing disable_IO_APIC(). However, my patch should be work well (and
>> has already been merged to -tip tree). So how about taking my patch at
>> first, and then discussing the removal of disabled_IO_APIC()?
>
> It doesn't matter to me.  My orignal patch last year was similar to yours
> until it was suggested that we were working around a problem which was we
> shouldn't touch the IO_APIC code on panic.  Then I wrote the removal of
> disable_IO_APIC patch and did lots of testing on it.  I don't think I have
> seen any issues with it (just the removal of disabling the lapic stuff).

Yes, you really did a lot of testing about this problem according to
your patch(https://lkml.org/lkml/2012/1/31/391). Although you
said jiffies calibration code does not need the PIT in
http://lists.infradead.org/pipermail/kexec/2012-February/006017.html,
I don't understand yet why we can remove disable_IO_APIC.
Would you please explain about the calibration codes?

By the way, can we remove disable_IO_APIC even if an old dump capture
kernel is used?

Thanks,
Yoshihiro YUNOMAE

> Regardless, your patch fixes a similar problem we saw on RHEL, so I am
> happy either way.  The removal of the disable_IO_APIC() just makes the
> code look cleaner.
>
> Cheers,
> Don
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
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>

-- 
Yoshihiro YUNOMAE
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: yoshihiro.yunomae.ez@hitachi.com

Re: Re: Re: [PATCH] [BUGFIX] crash/ioapic: Prevent crash_kexec() from deadlocking of ioapic_lock

[Don Zickus]

On Tue, Aug 27, 2013 at 12:41:51PM +0900, Yoshihiro YUNOMAE wrote:
> Hi Don,
> 
> Sorry for the late reply.
> 
> (2013/08/22 22:11), Don Zickus wrote:
> >On Thu, Aug 22, 2013 at 05:38:07PM +0900, Yoshihiro YUNOMAE wrote:
> >>>So, I agree with Eric, let's remove the disable_IO_APIC() stuff and keep
> >>>the code simpler.
> >>
> >>Thank you for commenting about my patch.
> >>I didn't know you already have submitted the patches for this deadlock
> >>problem.
> >>
> >>I can't answer definitively right now that no problems are induced by
> >>removing disable_IO_APIC(). However, my patch should be work well (and
> >>has already been merged to -tip tree). So how about taking my patch at
> >>first, and then discussing the removal of disabled_IO_APIC()?
> >
> >It doesn't matter to me.  My orignal patch last year was similar to yours
> >until it was suggested that we were working around a problem which was we
> >shouldn't touch the IO_APIC code on panic.  Then I wrote the removal of
> >disable_IO_APIC patch and did lots of testing on it.  I don't think I have
> >seen any issues with it (just the removal of disabling the lapic stuff).
> 
> Yes, you really did a lot of testing about this problem according to
> your patch(https://lkml.org/lkml/2012/1/31/391). Although you
> said jiffies calibration code does not need the PIT in
> http://lists.infradead.org/pipermail/kexec/2012-February/006017.html,
> I don't understand yet why we can remove disable_IO_APIC.
> Would you please explain about the calibration codes?

I forgot a lot of this, Eric B. might remember more (as he was the one that
pointed this out initially).  I believe initially the io_apic had to be in
a pre-configured state in order to do some early calibration of the timing
code.  Later on, it was my understanding, that the calibration of various
time keeping stuff did not need the io_apic in a correct state.  The code
might have switched to tsc instead of PIT, I forget.

Then again looking at the output of the latest dmesg, it seems the IO APIC
is initialized way before the tsc is calibrated.  So I am not sure what
needed to get done or what interrupts are needed before the IO APIC gets
initialized.


> 
> By the way, can we remove disable_IO_APIC even if an old dump capture
> kernel is used?

Good question.  I did a bunch of testing with RHEL-6 too, which is 2.6.32
based.  But I think we added some IRR fixes (commit 1e75b31d638), which
may or may not have helped in this case.  So I don't know when a kernel
started worked correctly during init (with the right changes).  I believe
2.6.32 had everything.

However, at the same time, the memory layout of current kernels has
changed and I am not sure if older kernels can read them correctly (or if
you just need the latest makedumpfile tool).  In other words, an old
kernel like 2.6.32 might not work as a kdump kernel for a 3.10 kernel.  I
don't know.

How old is the kernel you are working with?

Cheers,
Don

Re: [PATCH] [BUGFIX] crash/ioapic: Prevent crash_kexec() from deadlocking of ioapic_lock

[Eric W. Biederman]

Don Zickus <dzickus@redhat.com> writes:

> On Tue, Aug 27, 2013 at 12:41:51PM +0900, Yoshihiro YUNOMAE wrote:
>> Hi Don,
>> 
>> Sorry for the late reply.
>> 
>> (2013/08/22 22:11), Don Zickus wrote:
>> >On Thu, Aug 22, 2013 at 05:38:07PM +0900, Yoshihiro YUNOMAE wrote:
>> >>>So, I agree with Eric, let's remove the disable_IO_APIC() stuff and keep
>> >>>the code simpler.
>> >>
>> >>Thank you for commenting about my patch.
>> >>I didn't know you already have submitted the patches for this deadlock
>> >>problem.
>> >>
>> >>I can't answer definitively right now that no problems are induced by
>> >>removing disable_IO_APIC(). However, my patch should be work well (and
>> >>has already been merged to -tip tree). So how about taking my patch at
>> >>first, and then discussing the removal of disabled_IO_APIC()?
>> >
>> >It doesn't matter to me.  My orignal patch last year was similar to yours
>> >until it was suggested that we were working around a problem which was we
>> >shouldn't touch the IO_APIC code on panic.  Then I wrote the removal of
>> >disable_IO_APIC patch and did lots of testing on it.  I don't think I have
>> >seen any issues with it (just the removal of disabling the lapic stuff).
>> 
>> Yes, you really did a lot of testing about this problem according to
>> your patch(https://lkml.org/lkml/2012/1/31/391). Although you
>> said jiffies calibration code does not need the PIT in
>> http://lists.infradead.org/pipermail/kexec/2012-February/006017.html,
>> I don't understand yet why we can remove disable_IO_APIC.
>> Would you please explain about the calibration codes?
>
> I forgot a lot of this, Eric B. might remember more (as he was the one that
> pointed this out initially).  I believe initially the io_apic had to be in
> a pre-configured state in order to do some early calibration of the timing
> code.  Later on, it was my understanding, that the calibration of various
> time keeping stuff did not need the io_apic in a correct state.  The code
> might have switched to tsc instead of PIT, I forget.

Yes.  Alan Coxe's initial SMP port had a few cases where it still
exepected the system to be in PIT mode during boot and it took us a
decade or so before those assumptions were finally expunged.

> Then again looking at the output of the latest dmesg, it seems the IO APIC
> is initialized way before the tsc is calibrated.  So I am not sure what
> needed to get done or what interrupts are needed before the IO APIC gets
> initialized.

The practical issue is that jiffies was calibrated off of the PIT timer
if I recall.  But that is all old news.

>> By the way, can we remove disable_IO_APIC even if an old dump capture
>> kernel is used?
>
> Good question.  I did a bunch of testing with RHEL-6 too, which is 2.6.32
> based.  But I think we added some IRR fixes (commit 1e75b31d638), which
> may or may not have helped in this case.  So I don't know when a kernel
> started worked correctly during init (with the right changes).  I believe
> 2.6.32 had everything.

A sufficient old and buggy dump capture kernel will fail because of bugs
in it's startup path, but I don't think anyone cares.

The kernel startup path has been fixed for years, and disable_IO_APIC in
crash_kexec has always been a bug work-around for deficiencies in the
kernel's start up path (not part of the guaranteed interface).
Furthermore every real system configuration I have encountered used the
same kernel version for the crashdump kernel and the production kernel.
So we should be good.

> However, at the same time, the memory layout of current kernels has
> changed and I am not sure if older kernels can read them correctly (or if
> you just need the latest makedumpfile tool).  In other words, an old
> kernel like 2.6.32 might not work as a kdump kernel for a 3.10 kernel.  I
> don't know.

Memory layout should not be an issue at all.  The details are passed
from one kernel to another in a set of ELF headers.  So if the crash
dump kernel can run in the memory reserved for it, all should work well.

Eric

Re: Re: [PATCH] [BUGFIX] crash/ioapic: Prevent crash_kexec() from deadlocking of ioapic_lock

[Yoshihiro YUNOMAE]

Hi Eric and Don,

Sorry for the late reply.

(2013/08/31 9:58), Eric W. Biederman wrote:
> Don Zickus <dzickus@redhat.com> writes:
> 
>> On Tue, Aug 27, 2013 at 12:41:51PM +0900, Yoshihiro YUNOMAE wrote:
>>> Hi Don,
>>>
>>> Sorry for the late reply.
>>>
>>> (2013/08/22 22:11), Don Zickus wrote:
>>>> On Thu, Aug 22, 2013 at 05:38:07PM +0900, Yoshihiro YUNOMAE wrote:
>>>>>> So, I agree with Eric, let's remove the disable_IO_APIC() stuff and keep
>>>>>> the code simpler.
>>>>>
>>>>> Thank you for commenting about my patch.
>>>>> I didn't know you already have submitted the patches for this deadlock
>>>>> problem.
>>>>>
>>>>> I can't answer definitively right now that no problems are induced by
>>>>> removing disable_IO_APIC(). However, my patch should be work well (and
>>>>> has already been merged to -tip tree). So how about taking my patch at
>>>>> first, and then discussing the removal of disabled_IO_APIC()?
>>>>
>>>> It doesn't matter to me.  My orignal patch last year was similar to yours
>>>> until it was suggested that we were working around a problem which was we
>>>> shouldn't touch the IO_APIC code on panic.  Then I wrote the removal of
>>>> disable_IO_APIC patch and did lots of testing on it.  I don't think I have
>>>> seen any issues with it (just the removal of disabling the lapic stuff).
>>>
>>> Yes, you really did a lot of testing about this problem according to
>>> your patch(https://lkml.org/lkml/2012/1/31/391). Although you
>>> said jiffies calibration code does not need the PIT in
>>> http://lists.infradead.org/pipermail/kexec/2012-February/006017.html,
>>> I don't understand yet why we can remove disable_IO_APIC.
>>> Would you please explain about the calibration codes?
>>
>> I forgot a lot of this, Eric B. might remember more (as he was the one that
>> pointed this out initially).  I believe initially the io_apic had to be in
>> a pre-configured state in order to do some early calibration of the timing
>> code.  Later on, it was my understanding, that the calibration of various
>> time keeping stuff did not need the io_apic in a correct state.  The code
>> might have switched to tsc instead of PIT, I forget.
> 
> Yes.  Alan Coxe's initial SMP port had a few cases where it still
> exepected the system to be in PIT mode during boot and it took us a
> decade or so before those assumptions were finally expunged.

Would you please tell me the commit ID or the hint like files,
functions, or when?

>> Then again looking at the output of the latest dmesg, it seems the IO APIC
>> is initialized way before the tsc is calibrated.  So I am not sure what
>> needed to get done or what interrupts are needed before the IO APIC gets
>> initialized.
> 
> The practical issue is that jiffies was calibrated off of the PIT timer
> if I recall.  But that is all old news.

Are the jiffies calibration codes calibrate_delay()?
It seems that the jiffies calibration have not used PIT in 2005
according to 8a9e1b0.

>>> By the way, can we remove disable_IO_APIC even if an old dump capture
>>> kernel is used?
>>
>> Good question.  I did a bunch of testing with RHEL-6 too, which is 2.6.32
>> based.  But I think we added some IRR fixes (commit 1e75b31d638), which
>> may or may not have helped in this case.  So I don't know when a kernel
>> started worked correctly during init (with the right changes).  I believe
>> 2.6.32 had everything.
> 
> A sufficient old and buggy dump capture kernel will fail because of bugs
> in it's startup path, but I don't think anyone cares.

OK, if the jiffies calibration problem has been fixed in the old days,
we don't need to care for the old kernel.

> The kernel startup path has been fixed for years, and disable_IO_APIC in
> crash_kexec has always been a bug work-around for deficiencies in the
> kernel's start up path (not part of the guaranteed interface).
> Furthermore every real system configuration I have encountered used the
> same kernel version for the crashdump kernel and the production kernel.
> So we should be good.

We also will be use the kdump(crashdump) kernel as the production
kernel. Should I only care for the current kernel?

Thanks,
Yoshihiro YUNOMAE

-- 
Yoshihiro YUNOMAE
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: yoshihiro.yunomae.ez@hitachi.com

Re: [PATCH] [BUGFIX] crash/ioapic: Prevent crash_kexec() from deadlocking of ioapic_lock

[Eric W. Biederman]

Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@hitachi.com> writes:

> Hi Eric and Don,
>
> Sorry for the late reply.
>
> (2013/08/31 9:58), Eric W. Biederman wrote:
>> Don Zickus <dzickus@redhat.com> writes:
>> 
>>> On Tue, Aug 27, 2013 at 12:41:51PM +0900, Yoshihiro YUNOMAE wrote:
>>>> Hi Don,
>>>>
>>>> Sorry for the late reply.
>>>>
>>>> (2013/08/22 22:11), Don Zickus wrote:
>>>>> On Thu, Aug 22, 2013 at 05:38:07PM +0900, Yoshihiro YUNOMAE wrote:
>>>>>>> So, I agree with Eric, let's remove the disable_IO_APIC() stuff and keep
>>>>>>> the code simpler.
>>>>>>
>>>>>> Thank you for commenting about my patch.
>>>>>> I didn't know you already have submitted the patches for this deadlock
>>>>>> problem.
>>>>>>
>>>>>> I can't answer definitively right now that no problems are induced by
>>>>>> removing disable_IO_APIC(). However, my patch should be work well (and
>>>>>> has already been merged to -tip tree). So how about taking my patch at
>>>>>> first, and then discussing the removal of disabled_IO_APIC()?
>>>>>
>>>>> It doesn't matter to me.  My orignal patch last year was similar to yours
>>>>> until it was suggested that we were working around a problem which was we
>>>>> shouldn't touch the IO_APIC code on panic.  Then I wrote the removal of
>>>>> disable_IO_APIC patch and did lots of testing on it.  I don't think I have
>>>>> seen any issues with it (just the removal of disabling the lapic stuff).
>>>>
>>>> Yes, you really did a lot of testing about this problem according to
>>>> your patch(https://lkml.org/lkml/2012/1/31/391). Although you
>>>> said jiffies calibration code does not need the PIT in
>>>> http://lists.infradead.org/pipermail/kexec/2012-February/006017.html,
>>>> I don't understand yet why we can remove disable_IO_APIC.
>>>> Would you please explain about the calibration codes?
>>>
>>> I forgot a lot of this, Eric B. might remember more (as he was the one that
>>> pointed this out initially).  I believe initially the io_apic had to be in
>>> a pre-configured state in order to do some early calibration of the timing
>>> code.  Later on, it was my understanding, that the calibration of various
>>> time keeping stuff did not need the io_apic in a correct state.  The code
>>> might have switched to tsc instead of PIT, I forget.
>> 
>> Yes.  Alan Coxe's initial SMP port had a few cases where it still
>> exepected the system to be in PIT mode during boot and it took us a
>> decade or so before those assumptions were finally expunged.
>
> Would you please tell me the commit ID or the hint like files,
> functions, or when?

The short version is last time we tilted at this windmill the only
problem we could find was nmi's caused by the nmi watchdog.

So as a bug work-around all we need to retain is disabling the nmi
watchdog in crash-kexec.

>>> Then again looking at the output of the latest dmesg, it seems the IO APIC
>>> is initialized way before the tsc is calibrated.  So I am not sure what
>>> needed to get done or what interrupts are needed before the IO APIC gets
>>> initialized.
>> 
>> The practical issue is that jiffies was calibrated off of the PIT timer
>> if I recall.  But that is all old news.
>
> Are the jiffies calibration codes calibrate_delay()?
> It seems that the jiffies calibration have not used PIT in 2005
> according to 8a9e1b0.

Exactly.  That was the original reason why we put in the code to
disable the IOAPIC and the local apic.  There might have been other
reasons but that was the primary.

>>>> By the way, can we remove disable_IO_APIC even if an old dump capture
>>>> kernel is used?
>>>
>>> Good question.  I did a bunch of testing with RHEL-6 too, which is 2.6.32
>>> based.  But I think we added some IRR fixes (commit 1e75b31d638), which
>>> may or may not have helped in this case.  So I don't know when a kernel
>>> started worked correctly during init (with the right changes).  I believe
>>> 2.6.32 had everything.
>> 
>> A sufficient old and buggy dump capture kernel will fail because of bugs
>> in it's startup path, but I don't think anyone cares.
>
> OK, if the jiffies calibration problem has been fixed in the old days,
> we don't need to care for the old kernel.

Exactly.  There may have been one or two other silly assumptions and to
the best of our knowledge all of those have been purged except the
assumption that an NMI watchdog won't happen between kernels and while
booting the kernel.

>> The kernel startup path has been fixed for years, and disable_IO_APIC in
>> crash_kexec has always been a bug work-around for deficiencies in the
>> kernel's start up path (not part of the guaranteed interface).
>> Furthermore every real system configuration I have encountered used the
>> same kernel version for the crashdump kernel and the production kernel.
>> So we should be good.
>
> We also will be use the kdump(crashdump) kernel as the production
> kernel. Should I only care for the current kernel?

For this particular issue yes.

In general it is important for there to be a stable interface between
the two kernels just so you are not required to use the same kernel
version, and so there is the possibility of using something besides a
linux kernel.

At the same time it has always been the targets kernel's responsibility
to sort out the hardware devices unless it can't possibily do it.  And
apics for the longest time were very very hard to reset in the target
kernel, but now that they are not.  It makes sense for time permitting
to remove the now unnecessary code in the crashing kernel.  Because
ultimately the less code we have the fewer possible ways we can fail
in a known broken kernel.

Eric

Re: Re: [PATCH] [BUGFIX] crash/ioapic: Prevent crash_kexec() from deadlocking of ioapic_lock

[Yoshihiro YUNOMAE]

(2013/09/03 9:12), Eric W. Biederman wrote:
>>>> Then again looking at the output of the latest dmesg, it seems the IO APIC
>>>> is initialized way before the tsc is calibrated.  So I am not sure what
>>>> needed to get done or what interrupts are needed before the IO APIC gets
>>>> initialized.
>>>
>>> The practical issue is that jiffies was calibrated off of the PIT timer
>>> if I recall.  But that is all old news.
>>
>> Are the jiffies calibration codes calibrate_delay()?
>> It seems that the jiffies calibration have not used PIT in 2005
>> according to 8a9e1b0.
> 
> Exactly.  That was the original reason why we put in the code to
> disable the IOAPIC and the local apic.  There might have been other
> reasons but that was the primary.

Thanks, but I have still a question for jiffies calibration.

When kernel boots, calibrate_delay_direct() will be called in
calibrate_delay() for calculating loops_per_jiffy.  Then,
calibrate_delay_direct() waits until jiffies is incremented.
I think this means PIT or HPET is still used for the calibration.
Is there something wrong with my understanding?
If wrong, how is jiffies incremented?

>>> The kernel startup path has been fixed for years, and disable_IO_APIC in
>>> crash_kexec has always been a bug work-around for deficiencies in the
>>> kernel's start up path (not part of the guaranteed interface).
>>> Furthermore every real system configuration I have encountered used the
>>> same kernel version for the crashdump kernel and the production kernel.
>>> So we should be good.
>>
>> We also will be use the kdump(crashdump) kernel as the production
>> kernel. Should I only care for the current kernel?
> 
> For this particular issue yes.
> 
> In general it is important for there to be a stable interface between
> the two kernels just so you are not required to use the same kernel
> version, and so there is the possibility of using something besides a
> linux kernel.

OK. In order to judge whether a kernel version as crashdump kernel is
usable or not, I want to understand why we can remove disable_IO_APIC
in detail.

> At the same time it has always been the targets kernel's responsibility
> to sort out the hardware devices unless it can't possibily do it.  And
> apics for the longest time were very very hard to reset in the target
> kernel, but now that they are not.  It makes sense for time permitting
> to remove the now unnecessary code in the crashing kernel.  Because
> ultimately the less code we have the fewer possible ways we can fail
> in a known broken kernel.

Yes, I agree with you.

Thanks,
Yoshihiro YUNOMAE

-- 
Yoshihiro YUNOMAE
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: yoshihiro.yunomae.ez@hitachi.com

Re: [PATCH] [BUGFIX] crash/ioapic: Prevent crash_kexec() from deadlocking of ioapic_lock

[Eric W. Biederman]

Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@hitachi.com> writes:

> (2013/09/03 9:12), Eric W. Biederman wrote:
>>>>> Then again looking at the output of the latest dmesg, it seems the IO APIC
>>>>> is initialized way before the tsc is calibrated.  So I am not sure what
>>>>> needed to get done or what interrupts are needed before the IO APIC gets
>>>>> initialized.
>>>>
>>>> The practical issue is that jiffies was calibrated off of the PIT timer
>>>> if I recall.  But that is all old news.
>>>
>>> Are the jiffies calibration codes calibrate_delay()?
>>> It seems that the jiffies calibration have not used PIT in 2005
>>> according to 8a9e1b0.
>> 
>> Exactly.  That was the original reason why we put in the code to
>> disable the IOAPIC and the local apic.  There might have been other
>> reasons but that was the primary.
>
> Thanks, but I have still a question for jiffies calibration.
>
> When kernel boots, calibrate_delay_direct() will be called in
> calibrate_delay() for calculating loops_per_jiffy.  Then,
> calibrate_delay_direct() waits until jiffies is incremented.
> I think this means PIT or HPET is still used for the calibration.
> Is there something wrong with my understanding?
> If wrong, how is jiffies incremented?

Things have definitely changed, and I believe part of what you are
seeing is the path when things are not calibrated by an arch specific
means.

Ulimately the issue was not that we waited (or possibly still wait) for
a timer interrupt to calibrate the delay loop.  The problem was that we
had initialized the interrupt controller in PIC mode (when the kernel
did not later use the interrupt controller in PIC mode) to receive the
interrupt.

The actual impetus for getting the last of the bugs shaken out is that
we have subarchitectures on x86 that do no support interrupt controllers
in PIC mode at all.

Recently the code seems to get reorganized every other year and I loose
track of the details of which piece of code is doing what, but the
general gist remains.

The key thing to look for is that we initialize the interrupt
controllers in apic mode before we receive interrupts.  That is really
the only thing that matters, and for a long time the calibration of the
delay loop was the one notable exception.

> OK. In order to judge whether a kernel version as crashdump kernel is
> usable or not, I want to understand why we can remove disable_IO_APIC
> in detail.

That sounds like responsible engineering.

>> At the same time it has always been the targets kernel's responsibility
>> to sort out the hardware devices unless it can't possibily do it.  And
>> apics for the longest time were very very hard to reset in the target
>> kernel, but now that they are not.  It makes sense for time permitting
>> to remove the now unnecessary code in the crashing kernel.  Because
>> ultimately the less code we have the fewer possible ways we can fail
>> in a known broken kernel.
>
> Yes, I agree with you.

Eric

Re: Re: [PATCH] [BUGFIX] crash/ioapic: Prevent crash_kexec() from deadlocking of ioapic_lock

[Yoshihiro YUNOMAE]

(2013/09/03 21:44), Eric W. Biederman wrote:
> Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@hitachi.com> writes:
> 
>> (2013/09/03 9:12), Eric W. Biederman wrote:
>>>>>> Then again looking at the output of the latest dmesg, it seems the IO APIC
>>>>>> is initialized way before the tsc is calibrated.  So I am not sure what
>>>>>> needed to get done or what interrupts are needed before the IO APIC gets
>>>>>> initialized.
>>>>>
>>>>> The practical issue is that jiffies was calibrated off of the PIT timer
>>>>> if I recall.  But that is all old news.
>>>>
>>>> Are the jiffies calibration codes calibrate_delay()?
>>>> It seems that the jiffies calibration have not used PIT in 2005
>>>> according to 8a9e1b0.
>>>
>>> Exactly.  That was the original reason why we put in the code to
>>> disable the IOAPIC and the local apic.  There might have been other
>>> reasons but that was the primary.
>>
>> Thanks, but I have still a question for jiffies calibration.
>>
>> When kernel boots, calibrate_delay_direct() will be called in
>> calibrate_delay() for calculating loops_per_jiffy.  Then,
>> calibrate_delay_direct() waits until jiffies is incremented.
>> I think this means PIT or HPET is still used for the calibration.
>> Is there something wrong with my understanding?
>> If wrong, how is jiffies incremented?
> 
> Things have definitely changed, and I believe part of what you are
> seeing is the path when things are not calibrated by an arch specific
> means.
> 
> Ulimately the issue was not that we waited (or possibly still wait) for
> a timer interrupt to calibrate the delay loop.  The problem was that we
> had initialized the interrupt controller in PIC mode (when the kernel
> did not later use the interrupt controller in PIC mode) to receive the
> interrupt.
> 
> The actual impetus for getting the last of the bugs shaken out is that
> we have subarchitectures on x86 that do no support interrupt controllers
> in PIC mode at all.

Is one of the subarchitectures Moorestown?

I found the Moorestown patch(05ddafb) which defined
pre_init_apic_IRQ0(). If this function will enable IOAPIC before using
timer(i.e. the function is called before calibrate_delay()), we will
be able to remove disable_IO_APIC. However, this function is a
Moorestown specific code, and normal PCs don't execute it.

I haven't find the generic cord which operates like pre_init_apic_IRQ0()
yet. Please tell me if you remember something.

Thanks,
Yoshihiro YUNOMAE

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Yoshihiro YUNOMAE
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: yoshihiro.yunomae.ez@hitachi.com