Re: [PATCH 2/3 v4] x86/topology: Avoid wasting 128k for package id array

[Prarit Bhargava <prarit@redhat.com>]

On 11/01/2017 12:56 PM, Thomas Gleixner wrote:
> On Wed, 25 Oct 2017, Prarit Bhargava wrote:
>> diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
>> index b390ff76e58f..f4ab1edf4e24 100644
>> --- a/arch/x86/include/asm/processor.h
>> +++ b/arch/x86/include/asm/processor.h
>> @@ -124,8 +124,10 @@ struct cpuinfo_x86 {
>>  	u16			booted_cores;
>>  	/* Physical processor id: */
>>  	u16			phys_proc_id;
>> -	/* Logical processor id: */
>> +	/* Logical processor (package) id: */
>>  	u16			logical_proc_id;
>> +	/* Physical package ID */
>> +	u16			phys_pkg_id;
> 
> How is this new field used aside of being written to and how is it
> different from phys_proc_id? AFAICT, it's the same as all callers to
> topology_update_package_map() are handing in cpu_data->phys_proc_id.
> 

I've removed this in v5.

>> +/**
>> + * topology_phys_to_logical_pkg - Map a physical package id to a logical
>> + *
>> + * Returns logical package id or -1 if not found
>> + */
>> +int topology_phys_to_logical_pkg(unsigned int phys_pkg)
>> +{
>> +	int log_pkg;
>> +
>> +	for (log_pkg = 0; log_pkg < logical_packages; log_pkg++)
>> +		if (logical_to_physical_pkg_map[log_pkg] == phys_pkg)
>> +			return log_pkg;
>> +
>> +	return -1;
>> +}
>> +EXPORT_SYMBOL(topology_phys_to_logical_pkg);
> 
> ....
> 
>> +
>> +	/* Allocate and copy a new array */
>> +	ltp_pkg_map_new = kmalloc(logical_packages * sizeof(u16), GFP_KERNEL);
>> +	BUG_ON(!ltp_pkg_map_new);
>> +	if (logical_to_physical_pkg_map) {
>> +		memcpy(ltp_pkg_map_new, logical_to_physical_pkg_map,
>> +		       logical_packages * sizeof(u16));
>> +		kfree(logical_to_physical_pkg_map);
>>  	}
>> -	physical_to_logical_pkg[pkg] = new;
>> +	logical_to_physical_pkg_map = ltp_pkg_map_new;
> 
> This lacks serialization and is therefore broken against a concurrent
> topology_phys_to_logical_pkg() call for obvious reasons. The current user
> is probably safe, but this really needs to be fixed now.

I'm using a spin_lock_irq in v5.

I am finishing testing on 4S & 8S systems now.

P.

> 
> Thanks,
> 
> 	tglx
>