linux-kernel - Re: [PATCH 1/2] percpu_ref: percpu_ref_tryget

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Date:   Thu, 21 Oct 2021 09:41:19 +0100
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     linux-block@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Christoph Lameter <cl@...ux.com>,
        Dennis Zhou <dennis@...nel.org>
Subject: Re: [PATCH 1/2] percpu_ref: percpu_ref_tryget_live() version holding
 RCU

On 10/20/21 21:10, Tejun Heo wrote:
> On Wed, Oct 20, 2021 at 09:03:18PM +0100, Pavel Begunkov wrote:
>> +/**
>> + * percpu_ref_tryget_live_rcu - same as percpu_ref_tryget_live() but the
>> + * caller is responsible for taking RCU.
>> + *
>> + * This function is safe to call as long as @ref is between init and exit.
>> + */
>> +static inline bool percpu_ref_tryget_live_rcu(struct percpu_ref *ref)
>> +{
>> +	unsigned long __percpu *percpu_count;
>> +	bool ret = false;
>> +
>> +	if (likely(__ref_is_percpu(ref, &percpu_count))) {
>> +		this_cpu_inc(*percpu_count);
>> +		ret = true;
>> +	} else if (!(ref->percpu_count_ptr & __PERCPU_REF_DEAD)) {
>> +		ret = atomic_long_inc_not_zero(&ref->data->count);
>> +	}
>> +	return ret;
>> +}
> 
> Can we please add rcu_read_lock_held() assertion? Other than that, looks
> fine to me.

Will add, thanks

-- 
Pavel Begunkov