Question about using spinlock to synchronize between kernel driver and an interrupt handler

[m silverstri]

On Sat, Feb 1, 2014 at 5:34 AM, Josh Cartwright <joshc at eso.teric.us> wrote:
> On Sat, Feb 01, 2014 at 01:32:49AM -0800, anish singh wrote:
>> On Sat, Feb 1, 2014 at 1:15 AM, m silverstri
>> <michael.j.silverstri at gmail.com> wrote:
>> > By driver code , I mean the code which set the register values and
>> > wait till the values is set (via an interrupt handler) before
>> > continues doing something else
>> ok so you are looking for below code:
>>
>>
>> some_func()
>> {
>> set_register_value
>> x_variable=0
>> wait_for_event*(x_variable);
>> }
>>
>> interrupt_handler(){
>> x_variable=1
>> wake_up();
>> }
>>
>> request_irq(interrupt_handler);
>
> Please investigate the usage of completions in your driver.  See
> include/linux/completion.h.  It sounds like it fits your usecase nicely.
>
>   Josh

I have loooked at linux completion for my usecase
So I think I can do

DECLARE_COMPLETION(my_completion);

some_func()
{
set_register_value
wait_for_completion(my_completion);
}

interrupt_handler(){
complete(my_completion);
}

request_irq(interrupt_handler);


My question now is what if 1 kernel thread execute some_funct(), but
before interrupt_handler() get invoked (from HW), another kernel
thread executes some_func(). In essence, set_register_value is execute
twice before interrupt_handler() return once.

how can I prevent another kernel thread from executing
"set_register_value()" when 1 is wait_for_completion?