linux-kernel - Re: [PATCH v3] random: remove batched entropy locking

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Message-ID: <Yf1M3YGVq71oC9BM@linutronix.de>
Date:   Fri, 4 Feb 2022 16:57:17 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     Andy Lutomirski <luto@...capital.net>,
        Boqun Feng <boqun.feng@...il.com>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Waiman Long <longman@...hat.com>,
        Sultan Alsawaf <sultan@...neltoast.com>,
        Theodore Ts'o <tytso@....edu>,
        Andy Lutomirski <luto@...nel.org>,
        Jonathan Neuschäfer <j.neuschaefer@....net>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v3] random: remove batched entropy locking

On 2022-02-04 16:51:42 [+0100], Jason A. Donenfeld wrote:
> index 455615ac169a..3e54b90a3ff8 100644
> --- a/drivers/char/random.c
> +++ b/drivers/char/random.c
> @@ -1759,41 +1762,54 @@ u64 get_random_u64(void)
>  	unsigned long flags;
>  	struct batched_entropy *batch;
>  	static void *previous;
> +	int next_gen;
>  
>  	warn_unseeded_randomness(&previous);
>  
> -	batch = raw_cpu_ptr(&batched_entropy_u64);
> -	spin_lock_irqsave(&batch->batch_lock, flags);
> -	if (batch->position % ARRAY_SIZE(batch->entropy_u64) == 0) {
> +	batch = this_cpu_ptr(&batched_entropy_u64);
> +	local_lock_irqsave(&batch->lock, flags);

Does this compile and work? From the looks of it, this should be:

	local_lock_irqsave(&batched_entropy_u64.lock, flags);
	batch = this_cpu_ptr(&batched_entropy_u64);

and we could do s/this_cpu_ptr/raw_cpu_ptr/

Sebastian