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

[ryan@bluewatersys.com (Ryan Mallon)]

Russell King - ARM Linux wrote:
> On Fri, Dec 18, 2009 at 02:25:03PM +0000, Russell King - ARM Linux wrote:
>> On Fri, Dec 18, 2009 at 02:11:00PM +0000, Russell King - ARM Linux wrote:
>>> 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.
>> Something like this:
> 
> Actually, I think we should go further and kill off THREAD_NOTIFY_RELEASE
> completely.  Added a few more people because EP93xx and PXA (well,
> Xscale) is now impacted by this change.

Hi Russell,

I haven't been following this discussion. Can you explain how I can test
to see if this works correctly, and I'll try and find some time to run it.

~Ryan