linux-kernel - Re: [PATCH v6] random: defer fast pool mixing to worker

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Message-ID: <YgoeBYJ5nwc8BTG3@linutronix.de>
Date:   Mon, 14 Feb 2022 10:16:53 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Theodore Ts'o <tytso@....edu>,
        Sultan Alsawaf <sultan@...neltoast.com>,
        Jonathan Neuschäfer <j.neuschaefer@....net>,
        Dominik Brodowski <linux@...inikbrodowski.net>
Subject: Re: [PATCH v6] random: defer fast pool mixing to worker

On 2022-02-13 18:37:33 [+0100], Jason A. Donenfeld wrote:
> I started looking at this and came up with this draft with questions:
> https://git.kernel.org/pub/scm/linux/kernel/git/crng/random.git/commit/?h=jd/no-irq-trylocks

to
| - Does anything anywhere call get_random_xx() before the worker has a
|   chance to run?

Once you queue a work item I don't think that the scheduler needs to put
it on the CPU right away. It may have already have other tasks waiting
including some with a RT priority.
Also, the lock is irqsave() so they can be users in an interrupt
handler. I remember the original reason why I made it irqsave is because
something did kmalloc() and SLUB somehow asked for random bits.

> Some research remains...
> 
> Jason

Sebastian