linux-kernel - Re: [PATCH v2] random: remove batched entropy locking

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Date:   Fri, 4 Feb 2022 12:10:13 +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 v2] random: remove batched entropy locking

On 2022-02-04 01:27:55 [+0100], Jason A. Donenfeld wrote:
> Hey Andy,
> 
> Think I could bug you to review this patch? The general idea is based
> on your original patch, and I think this fits what we talked about on
> IRC. I figure we'll probably both page this out of our minds after
> another week or two of not thinking about it.
> 
> It's here on cgit if that's easier to look at:
> https://git.kernel.org/pub/scm/linux/kernel/git/crng/random.git/commit/?h=jd/no-batch-lock

Please don't merge this:
- This splat only occurs with CONFIG_PROVE_RAW_LOCK_NESTING enabled.
  This option has this in its description:
  │ NOTE: There are known nesting problems. So if you enable this
  │ option expect lockdep splats until these problems have been fully
  │ addressed which is work in progress. This config switch allows to
  │ identify and analyze these problems. It will be removed and the
  │ check permanently enabled once the main issues have been fixed.

- The problem identified by the splat affects only PREEMPT_RT. Non-RT is
  not affected by this.

- This patch disables interrupts and invokes extract_crng() which leads
  to other problems.


If this patch is the way then it should be merged together with the
other outstanding issues.

> Thanks,
> Jason

Sebastian