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

[Denis Kirjanov]

On Monday, November 7, 2016, Gautham R Shenoy <ego at linux.vnet.ibm.com>
wrote:

> 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.
>
>
that's why I put the comment


> >     [   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 <kda at linux-powerpc.org <javascript:;>>
> >
> > v2:  wrap powernv_cpufreq_throttle_check()
> > as suggested by Gautham R Shenoy
>
> Looks good otherwise.
>
> Reviewed-by: Gautham R. Shenoy <ego at linux.vnet.ibm.com <javascript:;>>
>
> > ---
> >  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
> >
>
>
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