netdev - Re: [DRAFT PATCH] random32: make prandom

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Message-ID: <CAHk-=wiSbHyA3zpkNVf9G8uHDJ=JF12iUjMRH5h65DQf8VXDtg@mail.gmail.com>
Date:   Mon, 10 Aug 2020 10:45:26 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Willy Tarreau <w@....eu>
Cc:     George Spelvin <lkml@....org>, Netdev <netdev@...r.kernel.org>,
        Amit Klein <aksecurity@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Andrew Lutomirski <luto@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        "Theodore Ts'o" <tytso@....edu>,
        Marc Plumb <lkml.mplumb@...il.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Florian Westphal <fw@...len.de>
Subject: Re: [DRAFT PATCH] random32: make prandom_u32() output unpredictable

On Mon, Aug 10, 2020 at 9:59 AM Willy Tarreau <w@....eu> wrote:
>
> I took what we were already using in add_interrupt_randomness() since
> I considered that if it was acceptable there, it probably was elsewhere.

Once you've taken an interrupt, you're doing IO anyway, and the
interrupt costs will dominate anything you do.

But the prandom_u32() interface is potentially done many times per
interrupt. For all I know it's done inside fairly critical locks etc
too.

So I don't think one usage translates to another very well.

              Linus