[Xen-devel] Re: [PATCH] Fix cpu online/offline bug: mce memory leak.

[Keir Fraser <keir.xen@xxxxxxxxx>]

A further comment: Please remove the presmp_initcall(intel_mce_initcall)
altogether. It will be causing unnecessary memory allocations even on
non-Intel CPUs. Instead, I suggest to register the cpu_notifier from
intel_mcheck_init(), at the same time you allocate the mcabanks for CPU0.
This will ensure that the CMCI/allocation work in the notifier is only
attempted for suitably MCA-capable Intel processors.

Um, also, you should fail CPU_UP_PREPARE if cpu_mcabank_alloc() fails. CPU
bringup will probably fail anyway if you are that low on memory. I don't
think it makes sense to struggle on with hobbled MCA support for the new
processor in this case. If cpu_mcabank_alloc() fails for CPU0, called from
intel_mcheck_init() you can quite reasonably BUG() on that.

 -- Keir

On 01/03/2011 09:30, "Keir Fraser" <keir.xen@xxxxxxxxx> wrote:

> Some comments inline below. Overall a good patch to have, but needs some
> minor adjustments!
> 
>  -- Keir
> 
> On 01/03/2011 09:09, "Liu, Jinsong" <jinsong.liu@xxxxxxxxx> wrote:
> 
>> Fix cpu online/offline bug: mce memory leak.
>> 
>> Current Xen mce logic didn't free mcabanks. This would be a memory leak when
>> cpu offline.
>> When repeatly do cpu online/offline, this memory leak would make xenpool
>> shrink, and at a time point,
>> will call alloc_heap_pages --> flush_area_mask, which
>> ASSERT(local_irq_is_enabled()).
>> However, cpu online is irq disable, so it finally result in Xen crash.
>> 
>> This patch fix the memory leak bug, and tested OK over 110,000 round cpu
>> online/offline.
>> 
>> Signed-off-by: Liu, Jinsong <jinsong.liu@xxxxxxxxx>
>> 
>> diff -r 1a364b17d66a xen/arch/x86/cpu/mcheck/mce_intel.c
>> --- a/xen/arch/x86/cpu/mcheck/mce_intel.c Fri Feb 25 01:26:01 2011 +0800
>> +++ b/xen/arch/x86/cpu/mcheck/mce_intel.c Mon Feb 28 19:19:20 2011 +0800
>> @@ -1227,9 +1227,24 @@ static void intel_init_mce(void)
>>      mce_uhandler_num = sizeof(intel_mce_uhandlers)/sizeof(struct
>> mca_error_handler);
>>  }
>>  
>> -static int intel_init_mca_banks(void)
>> +static void cpu_mcabank_free(unsigned int cpu)
>>  {
>> -    struct mca_banks *mb1, *mb2, * mb3;
>> +    struct mca_banks *mb1, *mb2, *mb3, *mb4;
>> +
>> +    mb1 = per_cpu(mce_clear_banks, cpu);
>> +    mb2 = per_cpu(no_cmci_banks, cpu);
>> +    mb3 = per_cpu(mce_banks_owned, cpu);
>> +    mb4 = per_cpu(poll_bankmask, cpu);
>> +
>> +    mcabanks_free(mb1);
>> +    mcabanks_free(mb2);
>> +    mcabanks_free(mb3);
>> +    mcabanks_free(mb4);
>> +}
>> +
>> +static void cpu_mcabank_alloc(unsigned int cpu)
>> +{
>> +    struct mca_banks *mb1, *mb2, *mb3;
>>  
>>      mb1 = mcabanks_alloc();
>>      mb2 = mcabanks_alloc();
>> @@ -1237,22 +1252,23 @@ static int intel_init_mca_banks(void)
>>      if (!mb1 || !mb2 || !mb3)
>>          goto out;
>>  
>> -    __get_cpu_var(mce_clear_banks) = mb1;
>> -    __get_cpu_var(no_cmci_banks) = mb2;
>> -    __get_cpu_var(mce_banks_owned) = mb3;
>> +    per_cpu(mce_clear_banks, cpu) = mb1;
>> +    per_cpu(no_cmci_banks, cpu) = mb2;
>> +    per_cpu(mce_banks_owned, cpu) = mb3;
>> +    return;
>>  
>> -    return 0;
>>  out:
>>      mcabanks_free(mb1);
>>      mcabanks_free(mb2);
>>      mcabanks_free(mb3);
>> -    return -ENOMEM;
>>  }
>>  
>>  /* p4/p6 family have similar MCA initialization process */
>>  enum mcheck_type intel_mcheck_init(struct cpuinfo_x86 *c)
>>  {
>> -    if (intel_init_mca_banks())
>> +    if ( !this_cpu(mce_clear_banks) ||
>> +         !this_cpu(no_cmci_banks)   ||
>> +         !this_cpu(mce_banks_owned) )
>>           return mcheck_none;
>>  
>>      intel_init_mca(c);
>> @@ -1301,13 +1317,19 @@ static int cpu_callback(
>>  static int cpu_callback(
>>      struct notifier_block *nfb, unsigned long action, void *hcpu)
>>  {
>> +    unsigned int cpu = (unsigned long)hcpu;
>> +
>>      switch ( action )
>>      {
>> +    case CPU_UP_PREPARE:
>> +        cpu_mcabank_alloc(cpu);
>> +        break;
>>      case CPU_DYING:
>>          cpu_mcheck_disable();
>>          break;
>>      case CPU_DEAD:
>>          cpu_mcheck_distribute_cmci();
>> +        cpu_mcabank_free(cpu);
>>          break;
> 
> You also need to cpu_mcabank_free(cpu) on CPU_UP_CANCELED. Else there's a
> memory leak on failed CPU bringup.
> 
>>      default:
>>          break;
>> @@ -1322,6 +1344,8 @@ static struct notifier_block cpu_nfb = {
>>  
>>  static int __init intel_mce_initcall(void)
>>  {
>> +    void *hcpu = (void *)(long)smp_processor_id();
>> +    cpu_callback(&cpu_nfb, CPU_UP_PREPARE, hcpu);
>>      register_cpu_notifier(&cpu_nfb);
>>      return 0;
>>  }
>> diff -r 1a364b17d66a xen/arch/x86/setup.c
>> --- a/xen/arch/x86/setup.c Fri Feb 25 01:26:01 2011 +0800
>> +++ b/xen/arch/x86/setup.c Mon Feb 28 19:19:20 2011 +0800
>> @@ -1203,6 +1203,8 @@ void __init __start_xen(unsigned long mb
>>  
>>      arch_init_memory();
>>  
>> +    do_presmp_initcalls();
>> +
>>      identify_cpu(&boot_cpu_data);
>>      if ( cpu_has_fxsr )
>>          set_in_cr4(X86_CR4_OSFXSR);
>> @@ -1235,8 +1237,6 @@ void __init __start_xen(unsigned long mb
>>      initialize_keytable();
>>  
>>      console_init_postirq();
>> -
>> -    do_presmp_initcalls();
> 
> This looks risky, especially so close to 4.1 release. Instead of moving
> do_presmp_initcalls(), please special-case cpu_mcabank_alloc() for CPU0 in
> intel_mcheck_init(), and remove your direct call to
> cpu_callback(...CPU_UP_PREPARE...) in intel_mce_initcall().
> 
>>      for_each_present_cpu ( i )
>>      {
> 
> 



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