linux-kernel - Re: [PATCH v2] random: set fast pool count to zero in cpuhp teardown

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Message-ID: <Ygpr9Xg0I+ZVzp9v@linutronix.de>
Date:   Mon, 14 Feb 2022 15:49:25 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Theodore Ts'o <tytso@....edu>,
        Jonathan Neuschäfer <j.neuschaefer@....net>,
        Sultan Alsawaf <sultan@...neltoast.com>,
        Dominik Brodowski <linux@...inikbrodowski.net>
Subject: Re: [PATCH v2] random: set fast pool count to zero in cpuhp teardown

On 2022-02-14 15:42:50 [+0100], Jason A. Donenfeld wrote:
> Hi Sebastian,
Hi Jason,

> If we move this to startup, is there a phase during which no interrupt
> will arrive? That is, can this happen very very early in startup, so
> that zeroing out count happens *before* ++count?

Interrupts will arrive starting with CPUHP_AP_ONLINE_IDLE from the CPU
HP point of view. My suggestion had a check for upper most bit and only
clear count if that bit was seen. So we wouldn't clear the counter if we
wouldn't suspect one of the rare corner cases.

> Jason

Sebastian