Re: [PATCH] percpu-refcount: relax limit on percpu_ref_reinit()
From: Tejun Heo <tj@kernel.org>
Date: 2018-09-10 16:49:28
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lkml
Hello, Ming. On Sun, Sep 09, 2018 at 08:58:24PM +0800, Ming Lei wrote:
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@@ -196,15 +197,6 @@ static void __percpu_ref_switch_to_percpu(struct percpu_ref *ref) atomic_long_add(PERCPU_COUNT_BIAS, &ref->count); - /* - * Restore per-cpu operation. smp_store_release() is paired - * with READ_ONCE() in __ref_is_percpu() and guarantees that the - * zeroing is visible to all percpu accesses which can see the - * following __PERCPU_REF_ATOMIC clearing. - */
So, while the location of percpu counter resetting moved, the pairing of store_release and READ_ONCE is still required to ensure that the clearing is visible before the switching to percpu mode becomes effective. Can you please rephrase and keep the above comment?
- for_each_possible_cpu(cpu) - *per_cpu_ptr(percpu_count, cpu) = 0; - smp_store_release(&ref->percpu_count_ptr, ref->percpu_count_ptr & ~__PERCPU_REF_ATOMIC); }
...
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@@ -357,10 +349,11 @@ EXPORT_SYMBOL_GPL(percpu_ref_kill_and_confirm); void percpu_ref_reinit(struct percpu_ref *ref) { unsigned long flags; + unsigned long __percpu *percpu_count; spin_lock_irqsave(&percpu_ref_switch_lock, flags); - WARN_ON_ONCE(!percpu_ref_is_zero(ref)); + WARN_ON_ONCE(__ref_is_percpu(ref, &percpu_count));
Can you elaborate this part? This doesn't seem required for the described change. Why is it part of the patch? Thanks. -- tejun