[PATCH] Prevent process migration during vfp_init()

[Hyungwoo Yang]

Hello,

I think I've found a bug but actually I'm not sure whether it only
happens to me due to our changes in kernel.

I really need your opinion.

In vfp_init() in "arch/arm/vfp/vfpmodule.c", if there is process
migration between vfp_enable() and smp_call_function() then kernel
crashes.

===== original code =====

       if (cpu_arch >= CPU_ARCH_ARMv6)
               vfp_enable(NULL); <== if migration happens just after
vfp_enable(NULL), kernel crashes.
                 :
                 :
       vfpsid = fmrx(FPSID); <== if migration happens, read tries to
access disbled VFP unit.
                 :
                 :
      if (VFP_arch)
               printk("not present\n");
       else if (vfpsid & FPSID_NODOUBLE) {
               printk("no double precision support\n");
       } else {
               hotcpu_notifier(vfp_hotplug, 0);

               smp_call_function(vfp_enable, NULL, 1); <== if migration happens,
smp_call_function will not work as it is expected.
=======================

Do you have any opinion?


There're a few ways of preventing migration (like set affinity or
disable premption) but the following is one of the way.
=======================