Re: Regression in 2.6.27-rc1 for set_cpus_allowed_ptr

["Rafael J. Wysocki" <rjw@sisk.pl>]

[Adding CCs]

On Friday, 8 of August 2008, Langsdorf, Mark wrote:
> One of my co-workers noticed that the powernow-k8
> driver no longer restarts when a CPU core is 
> hot-disabled and then hot-enabled on AMD quad-core
> systems.  
> 
> The following comands work fine on 2.6.26 and fail 
> on 2.6.27-rc1:
> 
> echo 0 > /sys/devices/system/cpu/cpu3/online
> echo 1 > /sys/devices/system/cpu/cpu3/online
> find /sys -name cpufreq
> 
> For 2.6.26, the find will return a cpufreq
> directory for each processor.  In 2.6.27-rc1,
> the cpu3 directory is missing.
> 
> After digging through the code, the following
> logic is failing when the core is hot-enabled
> at runtime.  The code works during the boot
> sequence.
> 
> 	cpumask_t = current->cpus_allowed;
> 	set_cpus_allowed_ptr(current, &cpumask_of_cpu(cpu));
> 	if (smp_processor_id() != cpu)
> 		return -ENODEV;
> 
> The objective is to move to the specific CPU and
> test it's MSRs to see if it is supported.  For
> some reason, it isn't working.  Any suggestions
> on how to fix this are appreciated.
> 
> -Mark Langdsorf
> Operating System Research Center
> AMD