linux-kernel - Re: [PATCH v2] random: unify cycles

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Date:   Fri, 25 Feb 2022 07:58:40 +0100
From:   Dominik Brodowski <linux@...inikbrodowski.net>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     linux-kernel@...r.kernel.org, Theodore Ts'o <tytso@....edu>
Subject: Re: [PATCH v2] random: unify cycles_t and jiffies usage and types

Am Thu, Feb 24, 2022 at 10:30:30PM +0100 schrieb Jason A. Donenfeld:
> @@ -1016,19 +1010,26 @@ struct timer_rand_state {
>   */
>  void add_device_randomness(const void *buf, size_t size)
>  {
> -	unsigned long time = random_get_entropy() ^ jiffies;
> -	unsigned long flags;
> +	cycles_t cycles = random_get_entropy();
> +	unsigned long now = jiffies, flags;

maybe "flags, now = jiffies" is a bit more reader-friendly?

>  static void add_timer_randomness(struct timer_rand_state *state, unsigned int num)
>  {
> -	struct {
> -		long jiffies;
> -		unsigned int cycles;
> -		unsigned int num;
> -	} sample;
> +	cycles_t cycles = random_get_entropy();
> +	unsigned long now = jiffies, flags;

Same here.

> @@ -1291,10 +1289,10 @@ static void mix_interrupt_randomness(struct work_struct *work)
>  void add_interrupt_randomness(int irq)
>  {
>  	enum { MIX_INFLIGHT = 1U << 31 };
> +	cycles_t cycles = random_get_entropy();
> +	unsigned long now = jiffies;
>  	struct fast_pool *fast_pool = this_cpu_ptr(&irq_randomness);
>  	struct pt_regs *regs = get_irq_regs();
> -	unsigned long now = jiffies;
> -	cycles_t cycles = random_get_entropy();
>  	unsigned int new_count;
>  
>  	if (cycles == 0)


Why do you change the ordering here?

Thanks,
	Dominik