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

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Message-ID: <YXB3n2pxiKYbd2Il@slm.duckdns.org>
Date:   Wed, 20 Oct 2021 10:10:07 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Pavel Begunkov <asml.silence@...il.com>
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 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.

Thanks.

-- 
tejun