linux-kernel - Re: [PATCH] random: mix hwgenerator randomness before sleeping

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Message-ID: <YnGI4lZVJ/FZEkcn@owl.dominikbrodowski.net>
Date:   Tue, 3 May 2022 21:56:18 +0200
From:   Dominik Brodowski <linux@...inikbrodowski.net>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] random: mix hwgenerator randomness before sleeping

Am Tue, May 03, 2022 at 09:51:41PM +0200 schrieb Jason A. Donenfeld:
> The add_hwgenerator_randomness() function is called in a loop from a
> kthread by the hwgenerator core. It's supposed to sleep when there's
> nothing to do, and wake up periodically for more entropy. Right now it
> receives entropy, sleeps, and then mixes it in. This commit reverses the
> order, so that it always mixes in entropy sooner and sleeps after. This
> way the entropy is more fresh.

... however, the hwgenerator may take quite some time to accumulate entropy
after wakeup. So now we might have a delay between a wakeup ("we need more
entropy!") and that entropy becoming available. Beforehand, the thread only 
went to sleep when there is no current need for "fresh" entropy.

Thanks,
	Dominik