linux-kernel - Re: [PATCH v3] cpufreq: powernv: fix stack bloat and hard limit on num cpus

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Message-ID: <8351130.8dpKiuZLPc@kreacher>
Date:   Mon, 04 Nov 2019 12:06:59 +0100
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        linux-pm@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v3] cpufreq: powernv: fix stack bloat and hard limit on num cpus

On Thursday, October 31, 2019 6:21:59 AM CET John Hubbard wrote:
> The following build warning occurred on powerpc 64-bit builds:
> 
> drivers/cpufreq/powernv-cpufreq.c: In function 'init_chip_info':
> drivers/cpufreq/powernv-cpufreq.c:1070:1: warning: the frame size of
> 1040 bytes is larger than 1024 bytes [-Wframe-larger-than=]
> 
> This is with a cross-compiler based on gcc 8.1.0, which I got from:
>   https://mirrors.edge.kernel.org/pub/tools/crosstool/files/bin/x86_64/8.1.0/
> 
> The warning is due to putting 1024 bytes on the stack:
> 
>     unsigned int chip[256];
> 
> ...and it's also undesirable to have a hard limit on the number of
> CPUs here.
> 
> Fix both problems by dynamically allocating based on num_possible_cpus,
> as recommended by Michael Ellerman.
> 
> Fixes: 053819e0bf840 ("cpufreq: powernv: Handle throttling due to Pmax capping at chip level")
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Cc: Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>
> Cc: Preeti U Murthy <preeti@...ux.vnet.ibm.com>
> Cc: Viresh Kumar <viresh.kumar@...aro.org>
> Cc: Rafael J. Wysocki <rjw@...ysocki.net>
> Cc: linux-pm@...r.kernel.org
> Cc: linuxppc-dev@...ts.ozlabs.org
> Signed-off-by: John Hubbard <jhubbard@...dia.com>
> Acked-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
> 
> Changes since v2: applied fixes from Michael Ellerman's review:
> 
> * Changed from CONFIG_NR_CPUS to num_possible_cpus()
> 
> * Fixed up commit description: added a note about exactly which
>   compiler generates the warning. And softened up wording about
>   the limitation on number of CPUs.
> 
> Changes since v1: includes Viresh's review commit fixes.

Applying as 5.5 material, thanks!