On 02/09/2013 05:14 AM, Paul E. McKenney wrote:
> On Tue, Jan 22, 2013 at 01:04:11PM +0530, Srivatsa S. Bhat wrote:
>> If interrupt handlers can also be readers, then one of the ways to make
>> per-CPU rwlocks safe, is to disable interrupts at the reader side before
>> trying to acquire the per-CPU rwlock and keep it disabled throughout the
>> duration of the read-side critical section.
[...]
>> -void percpu_read_lock(struct percpu_rwlock *pcpu_rwlock)
>> +void percpu_read_lock_irqsafe(struct percpu_rwlock *pcpu_rwlock)
>> {
>> preempt_disable();
>>
>> /* First and foremost, let the writer know that a reader is active */
>> - this_cpu_inc(*pcpu_rwlock->reader_refcnt);
>> + this_cpu_add(*pcpu_rwlock->reader_refcnt, READER_PRESENT);
>>
>> /*
>> * If we are already using per-cpu refcounts, it is not safe to switch
>> * the synchronization scheme. So continue using the refcounts.
>> */
>> if (reader_nested_percpu(pcpu_rwlock)) {
>> - goto out;
>> + this_cpu_inc(*pcpu_rwlock->reader_refcnt);
>
> Hmmm... If the reader is nested, it -doesn't- need the memory barrier at
> the end of this function. If there is lots of nesting, it might be
> worth getting rid of it.
>
Yes, good point! Will get rid of it.
Regards,
Srivatsa S. Bhat
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