Re: [PATCH v6 04/46] percpu_rwlock: Implement the core design ofPer-CPU Reader-Writer Locks

[Michel Lespinasse]

On Thu, Feb 28, 2013 at 3:25 AM, Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
> On 02/27, Michel Lespinasse wrote:
>>
>> +void lg_rwlock_local_read_lock(struct lgrwlock *lgrw)
>> +{
>> +       preempt_disable();
>> +
>> +       if (__this_cpu_read(*lgrw->local_refcnt) ||
>> +           arch_spin_trylock(this_cpu_ptr(lgrw->lglock->lock))) {
>> +               __this_cpu_inc(*lgrw->local_refcnt);
>
> Please look at __this_cpu_generic_to_op(). You need this_cpu_inc()
> to avoid the race with irs. The same for _read_unlock.

Hmmm, I was thinking that this was safe because while interrupts might
modify local_refcnt to acquire a nested read lock, they are expected
to release that lock as well which would set local_refcnt back to its
original value ???

-- 
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.
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