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

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Message-ID: <CAHmME9pO41uwYExSROc5X2+RE=a5tZfE=c=bAxVbhCHfa7=zSA@mail.gmail.com>
Date:   Fri, 4 Feb 2022 16:39:15 +0100
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
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

Hi Sebastian,

On Fri, Feb 4, 2022 at 3:30 PM Sebastian Andrzej Siewior
<bigeasy@...utronix.de> wrote:
> > What if we keep a spinlock_t there on PREEMPT_RT but stick with
> > disabling interrupts on !PREEMPT_RT? I wish there was a solution or an
> > API that amounted to the same thing so there wouldn't need to be an
> > #ifdef, but I don't know what that'd be.
>
> If it is still to much try to look for locallock_t and
> local_lock_irqsave(). This is kind of like your local_irq_save() but
> you have lockdep annotations and PREEMPT_RT has a spinlock_t like
> behaviour. It also documents in-code what the scope of your locking is.

Oh, that's terrific, thanks! Sounds like exactly what we were looking
for. I'll respin this patch with that.

Jason