linux-kernel - Re: [PATCH] kernel/isolation: Asset that a housekeeping CPU comes up at boot time

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Message-Id: <1560151344.y4aukciain.astroid@bobo.none>
Date:   Mon, 10 Jun 2019 17:24:32 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Frederic Weisbecker <frederic@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] kernel/isolation: Asset that a housekeeping CPU comes up
 at boot time

Nicholas Piggin's on June 1, 2019 9:39 pm:
> With the change to allow the boot CPU0 to be isolated, it is possible
> to specify command line options that result in no housekeeping CPU
> online at boot.
> 
> An 8 CPU system booted with "nohz_full=0-6 maxcpus=4", for example.
> 
> It is not easily possible at housekeeping init time to know all the
> various SMP options that will result in an invalid configuration, so
> this patch adds a sanity check after SMP init, to ensure that a
> housekeeping CPU has been onlined.
> 
> The panic is undesirable, but it's better than the alternative of an
> obscure non deterministic failure. The panic will reliably happen
> when advanced parameters are used incorrectly.

Ping on this one? This should resolve Frederic's remaining objection
to the series (at least until he solves it more generally).

As the series has already been merged, should we get this upstream
before release?

Thanks,
Nick