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.
But otherwise I agree, looks like a clever and working idea to me.
And simple!
> There is an interesting case where lg_rwlock_local_read_lock could be
> interrupted after getting the local lglock but before incrementing
> local_refcnt to 1; if that happens any nested readers within that
> interrupt will have to take the global rwlock read side. I think this
> is perfectly acceptable
Agreed.
Or interrupt can do spin_trylock(percpu-lock) after we take the global
->fallback_rwlock (if we race with write_lock + write_unlock), but I do
not see any possible deadlock in this case.
Oleg.
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