linux-kernel - Re: [PATCH 5/5] random: Defer processing of randomness on PREEMPT

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Message-ID: <20211217022338.GA19411@gondor.apana.org.au>
Date:   Fri, 17 Dec 2021 13:23:38 +1100
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Jason@...c4.com, linux-kernel@...r.kernel.org, tytso@....edu,
        tglx@...utronix.de, peterz@...radead.org
Subject: Re: [PATCH 5/5] random: Defer processing of randomness on PREEMPT_RT.

Sebastian Andrzej Siewior <bigeasy@...utronix.de> wrote:
>
> Even the IOCTL path must spin with disabled interrupts to avoid dead
> locks. Therefore it makes no sense if attempt acquire the lock from
> process or IRQ context. Something like
>        while (!raw_spin_trylock_irqsave())
>                cpu_relax()

What about the TCP socket locking model?

IOW, the user-space slow path will add itself to a backlog queue
during contention, and the interrupt fast path will schedule work
to process any user-space backlog on exit.

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt