Re: [Xen-devel] Xen-unstable: Regression (on AMD) host boot stuck on (XEN) testing the IO APIC.......................

[Sander Eikelenboom <linux@xxxxxxxxxxxxxx>]

Tuesday, August 26, 2014, 11:32:10 AM, you wrote:

> On 26/08/14 08:45, Jan Beulich wrote:
>>>>> On 26.08.14 at 09:34, <JBeulich@xxxxxxxx> wrote:
>>> Considering how early this is, the only theory I have is that
>>> rcu_pending() may end up constantly returning true, thus always
>>> causing RCU_SOFTIRQ to get raised, not allowing the loop in
>>> __do_softirq() to ever exit. If that's the case, we seem to have
>>> two options:
>>> - pass into __print_IO_APIC() whether it's being called from a key
>>>   handler
>>> - only call process_pending_softirqs() when system_state >=
>>>   SYS_STATE_smp_boot
>>>
>>> Personally I'd prefer the former option.
>> So here's a patch implementing that (the issue clearly isn't limited
>> to AMD).
>>
>> Jan
>>
>> x86/IO-APIC: don't process softirqs during early boot
>>
>> Commit e13b320399 ("x86/irq: process softirqs in irq keyhandlers")
>> made this unconditional, but the boot time use of __print_IO_APIC()
>> (when "apic_verbosity=debug" was given) can't tolerate that.
>>
>> Reported-by: Sander Eikelenboom <linux@xxxxxxxxxxxxxx>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

> Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

And Tested-by:  Sander Eikelenboom <linux@xxxxxxxxxxxxxx>

Thanks again ! 

>>
>> --- a/xen/arch/x86/io_apic.c
>> +++ b/xen/arch/x86/io_apic.c
>> @@ -1092,7 +1092,7 @@ static inline void UNEXPECTED_IO_APIC(vo
>>  {
>>  }
>>  
>> -static void /*__init*/ __print_IO_APIC(void)
>> +static void /*__init*/ __print_IO_APIC(bool_t boot)
>>  {
>>      int apic, i;
>>      union IO_APIC_reg_00 reg_00;
>> @@ -1113,7 +1113,8 @@ static void /*__init*/ __print_IO_APIC(v
>>      printk(KERN_INFO "testing the IO APIC.......................\n");
>>  
>>      for (apic = 0; apic < nr_ioapics; apic++) {
>> -        process_pending_softirqs();
>> +        if ( !boot )
>> +            process_pending_softirqs();
>>  
>>          if (!nr_ioapic_entries[apic])
>>              continue;
>> @@ -1219,7 +1220,7 @@ static void /*__init*/ __print_IO_APIC(v
>>      for (i = 0; i < nr_irqs_gsi; i++) {
>>          struct irq_pin_list *entry = irq_2_pin + i;
>>  
>> -        if ( !(i & 0x1f) )
>> +        if ( !boot && !(i & 0x1f) )
>>              process_pending_softirqs();
>>  
>>          if (entry->pin < 0)
>> @@ -1242,12 +1243,12 @@ static void /*__init*/ __print_IO_APIC(v
>>  static void __init print_IO_APIC(void)
>>  {
>>      if (apic_verbosity != APIC_QUIET)
>> -        __print_IO_APIC();
>> +        __print_IO_APIC(1);
>>  }
>>  
>>  static void _print_IO_APIC_keyhandler(unsigned char key)
>>  {
>> -    __print_IO_APIC();
>> +    __print_IO_APIC(0);
>>  }
>>  static struct keyhandler print_IO_APIC_keyhandler = {
>>      .diagnostic = 1,
>>
>>
>>




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