[PATCH] arm: vfp: always clear vfp_current_hw_state when forcing reload

[Yuanyuan ZHONG]

On Fri, Oct 11, 2013 at 11:26 AM, Russell King - ARM Linux
<linux at arm.linux.org.uk> wrote:
> On Fri, Oct 11, 2013 at 11:12:19AM -0500, Yuanyuan ZHONG wrote:
>> On Fri, Oct 11, 2013 at 7:07 AM, Russell King - ARM Linux
>> <linux at arm.linux.org.uk> wrote:
>> > On Thu, Oct 10, 2013 at 11:00:18AM -0500, Yuanyuan ZHONG wrote:
>> >> Hi Russell, et al
>> >>
>> >> If there is no further comments, I'll submit it to patch system.
>> >> Thanks.
>> >
>> > No, I still don't agree with your patch as being the correct fix.  Look
>> > at the code that you're creating:
>> >
>> >         if (vfp_state_in_hw(cpu, thread)) {
>> >                 fmxr(FPEXC, fmrx(FPEXC) & ~FPEXC_EN);
>> >                 vfp_current_hw_state[cpu] = NULL;
>> >         }
>> > #ifdef CONFIG_SMP
>> >         thread->vfpstate.hard.cpu = NR_CPUS;
>> >         vfp_current_hw_state[cpu] = NULL;
>> > #endif
>> >
>> > So when SMP is enabled we unconditionally blat out the vfp_current_hw_state
>> > pointer for this CPU?
>>
>> I think ensuring local vfp_current_hw_state is invalidated is what
>> vfp_force_reload() need to do when SMP is enabled.
>
> vfp_force_reload() is about asking for the state S on CPU N to be
> reloaded.  It is not about merely asking for the state on CPU N to
> be reloaded.

Then this function cannot do what we need for cpu hotplug. At that
time we don't know if the state S on CPU N is valid, we can only ask
for the state on CPU N to be reloaded. How about this:

diff --git a/arch/arm/vfp/vfpmodule.c b/arch/arm/vfp/vfpmodule.c
index 52b8f40..efdd9e0 100644
--- a/arch/arm/vfp/vfpmodule.c
+++ b/arch/arm/vfp/vfpmodule.c
@@ -644,6 +644,7 @@ static int vfp_hotplug(struct notifier_block *b,
unsigned long action,
 {
        if (action == CPU_DYING || action == CPU_DYING_FROZEN) {
                vfp_force_reload((long)hcpu, current_thread_info());
+               vfp_current_hw_state[(long)hcpu] = NULL;
        } else if (action == CPU_STARTING || action == CPU_STARTING_FROZEN)
                vfp_enable(NULL);
        return NOTIFY_OK;