Subject: Re: [PATCH v2] ppc: cpufreq: disable preemption while checking CPU throttling state

From: Gautham R Shenoy <[email-masked]>
Date: Mon, 7 Nov 2016 08:01:47 +0530

Hi Denis,

On Fri, Nov 04, 2016 at 07:08:38AM -0400, Denis Kirjanov wrote:

You can provide the config option with which this bug was found in the
change log. I suppose you had enabled CONFIG_DEBUG_PREEMPT.

>     [   67.700897] BUG: using smp_processor_id() in preemptible [00000000] code: cat/7343
>     [   67.700988] caller is .powernv_cpufreq_throttle_check+0x2c/0x710
>     [   67.700998] CPU: 13 PID: 7343 Comm: cat Not tainted 4.8.0-rc5-dirty #1
>     [   67.701038] Call Trace:
>     [   67.701066] [c0000007d25b75b0] [c000000000971378] .dump_stack+0xe4/0x150 (unreliable)
>     [   67.701153] [c0000007d25b7640] [c0000000005162e4] .check_preemption_disabled+0x134/0x150
>     [   67.701238] [c0000007d25b76e0] [c0000000007b63ac] .powernv_cpufreq_throttle_check+0x2c/0x710
>     [   67.701322] [c0000007d25b7790] [c0000000007b6d18] .powernv_cpufreq_target_index+0x288/0x360
>     [   67.701407] [c0000007d25b7870] [c0000000007acee4] .__cpufreq_driver_target+0x394/0x8c0
>     [   67.701491] [c0000007d25b7920] [c0000000007b22ac] .cpufreq_set+0x7c/0xd0
>     [   67.701565] [c0000007d25b79b0] [c0000000007adf50] .store_scaling_setspeed+0x80/0xc0
>     [   67.701650] [c0000007d25b7a40] [c0000000007ae270] .store+0xa0/0x100
>     [   67.701723] [c0000007d25b7ae0] [c0000000003566e8] .sysfs_kf_write+0x88/0xb0
>     [   67.701796] [c0000007d25b7b70] [c0000000003553b8] .kernfs_fop_write+0x178/0x260
>     [   67.701881] [c0000007d25b7c10] [c0000000002ac3cc] .__vfs_write+0x3c/0x1c0
>     [   67.701954] [c0000007d25b7cf0] [c0000000002ad584] .vfs_write+0xc4/0x230
>     [   67.702027] [c0000007d25b7d90] [c0000000002aeef8] .SyS_write+0x58/0x100
>     [   67.702101] [c0000007d25b7e30] [c00000000000bfec] system_call+0x38/0xfc
> 
> Signed-off-by: Denis Kirjanov <[email-masked]>
> 
> v2:  wrap powernv_cpufreq_throttle_check()
> as suggested by Gautham R Shenoy

Looks good otherwise.

Reviewed-by: Gautham R. Shenoy <[email-masked]>

> ---
>  drivers/cpufreq/powernv-cpufreq.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/cpufreq/powernv-cpufreq.c b/drivers/cpufreq/powernv-cpufreq.c
> index d3ffde8..112e0e2 100644
> --- a/drivers/cpufreq/powernv-cpufreq.c
> +++ b/drivers/cpufreq/powernv-cpufreq.c
> @@ -647,8 +647,15 @@ static int powernv_cpufreq_target_index(struct cpufreq_policy *policy,
>  	if (unlikely(rebooting) && new_index != get_nominal_index())
>  		return 0;
> 
> -	if (!throttled)
> +	if (!throttled) {
> +		/*
> +		 * we don't want to be preempted while
> +		 * checking if the CPU frequency has been throttled
> +		 */
> +		preempt_disable();
>  		powernv_cpufreq_throttle_check(NULL);
> +		preempt_enable();
> +    }
> 
>  	cur_msec = jiffies_to_msecs(get_jiffies_64());
> 
> -- 
> 1.8.3.1
>