[PATCH] ARM: Fix a race in the vfp_notifier() function on SMP systems

[Russell King - ARM Linux]

On Fri, Dec 18, 2009 at 01:45:09PM +0000, Catalin Marinas wrote:
> 	(patch updated following Russell's changes to vfpmodule.c)
> 
> The vfp_notifier(THREAD_NOTIFY_RELEASE) maybe be called with thread->cpu
> different from the current one, causing a race condition with both the
> THREAD_NOTIFY_SWITCH path and vfp_support_entry().

How about we provide THREAD_NOTIFY_EXIT and call these hooks from
exit_thread() - we'll be calling the notifier when the thread is
still running, and so thread->cpu will be the local CPU.

This should be much safer all round, and give much simpler semantics
if we NULL out the current CPU's last_VFP_context pointer.  It also
means that each CPUs last_VFP_context pointer is only ever accessed
from the local CPU, which can only be a good thing.