linux-kernel - Re: [PATCH] cpufreq: powernv: fix stack bloat and NR

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Message-ID: <20191018042715.f76bawmoyk66isap@vireshk-i7>
Date:   Fri, 18 Oct 2019 09:57:15 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>, linux-pm@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] cpufreq: powernv: fix stack bloat and NR_CPUS limitation

On 17-10-19, 17:04, 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=]

How come we are catching this warning after 4 years ?

> 
> This is due to putting 1024 bytes on the stack:
> 
>     unsigned int chip[256];
> 
> ...and while looking at this, it also has a bug: it fails with a stack
> overrun, if CONFIG_NR_CPUS > 256.
> 
> Fix both problems by dynamically allocating based on CONFIG_NR_CPUS.
> 
> Fixes: 053819e0bf840 ("cpufreq: powernv: Handle throttling due to Pmax capping at chip level")
> 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>
> ---
> 
> Hi,
> 
> I have only compile-tested this, so I would appreciate if anyone
> could do a basic runtime test on it. But (famous last words) it
> seems simple enough that I'm confident it's correct. oh boy. :)
> 
> thanks,
> John Hubbard
> NVIDIA
> 
>  drivers/cpufreq/powernv-cpufreq.c | 17 +++++++++++++----
>  1 file changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/cpufreq/powernv-cpufreq.c b/drivers/cpufreq/powernv-cpufreq.c
> index 6061850e59c9..78e04402125f 100644
> --- a/drivers/cpufreq/powernv-cpufreq.c
> +++ b/drivers/cpufreq/powernv-cpufreq.c
> @@ -1041,9 +1041,14 @@ static struct cpufreq_driver powernv_cpufreq_driver = {
>  
>  static int init_chip_info(void)
>  {
> -	unsigned int chip[256];
> +	unsigned int *chip;
>  	unsigned int cpu, i;
>  	unsigned int prev_chip_id = UINT_MAX;
> +	int ret = 0;
> +
> +	chip = kcalloc(CONFIG_NR_CPUS, sizeof(int), GFP_KERNEL);

                                       sizeof(*chip)

> +	if (!chips)

           (!chip)

> +		return -ENOMEM;
>  
>  	for_each_possible_cpu(cpu) {
>  		unsigned int id = cpu_to_chip_id(cpu);
> @@ -1055,8 +1060,10 @@ static int init_chip_info(void)
>  	}
>  
>  	chips = kcalloc(nr_chips, sizeof(struct chip), GFP_KERNEL);
> -	if (!chips)
> -		return -ENOMEM;
> +	if (!chips) {
> +		ret = -ENOMEM;
> +		goto free_and_return;
> +	}
>  
>  	for (i = 0; i < nr_chips; i++) {
>  		chips[i].id = chip[i];
> @@ -1066,7 +1073,9 @@ static int init_chip_info(void)
>  			per_cpu(chip_info, cpu) =  &chips[i];
>  	}
>  
> -	return 0;
> +free_and_return:
> +	kfree(chip);
> +	return ret;
>  }
>  
>  static inline void clean_chip_info(void)
> -- 
> 2.23.0

-- 
viresh