In my opinion,i think spin lock is used for shot-time lock,if you lock
long term, cpu will miss the interrupts, i also have the question
about when we disable local interrupts,can the interrupt be delivered
to other cpus in SMP system?
BRs,
Lin
2009/5/19 raz ben yehuda <raziebe@xxxxxxxxx>:
>
> On Tue, 2009-05-19 at 00:49 +0700, Mulyadi Santosa wrote:
>> On Tue, May 19, 2009 at 12:33 AM, Ole Loots <ole@xxxxxxxxxxxxx> wrote:
>> > Hello to the list,
>> >
>> > I got a question about spinlocks. Here is some pseudo-code:
>> >
>> > my_external_int_handler(...)
>> > {
>> > spin_lock(&my_lock);
>> > // do things...
>> > spin_unlock(&my_lock);
>> > }
>> >
>> > my_ioctl_handler(ioctl_value)
>> > {
>> > switch(ioctl_value)
>> > {
>> > case xy:
>> > spin_lock_irqsave(&my_lock, flags);
>> > // do stuff
>> > spin_unlock_irqsave(&my_lock, flags);
>> > break;
>> > }
>> > }
>> >
>> > I just wan't to ensure that the interrupt is finished before I handle the
>> > IOCTL request, so that I'm not running into a race condition that would a
>> > affect an ring buffer.
>> > But what happens when an interrupt signal is triggered at the external
>> > interrupt pin, does spin_lock_irqsave que the interrupt? Or does it dismiss
>> > the interrupt? Does spinlock_irqsave mean I would miss an interrupt? If so,
>> > spinlock won't be the right thing to do...
>> >
>> > What I need is something like:
>> > while(interrupt_working){ sleep(); }
>> >
>> > How to do right?
>>
>> i think spinlock_irqsave means it disables the interrupt pins
>> temporarily but not nullifying the queued interrupts. Once it is
>> enabled again, it would fire the handler again.
>>
>> However, IIRC too, spin_lock_irqsave is disabling per CPU interrupt
>> line. So if you run your code in SMP or multicore, there is a chance
> please fix me if i am wrong.
> what spinlock_irqsave does is:
> 1. saves current of local interrupts.
> 2. disables local interrupts
> 3. acquires a lock
> any other context tries to to access the protected data will spin. else,
> how would you protect the data in SMP ?
>> of both interrupt and ioctl handlers try to access the data. Although
>> it is expected, perhaps you could consider using per CPU data ?
>>
>> regards,
>>
>> Mulyadi.
>>
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