Re: [PATCH] ppc: cpufreq: Use get_cpu()/put_cpu() instead of smp_processor_id() to avoid the oops

On Thursday, November 3, 2016, Gautham R Shenoy [off-list ref]
wrote:

Hi Denis,

On Thu, Nov 03, 2016 at 07:20:41AM -0400, Denis Kirjanov wrote:

quoted

[   67.700897] BUG: using smp_processor_id() in preemptible [00000000]

code: cat/7343

quoted

[   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)

quoted

[   67.701153] [c0000007d25b7640] [c0000000005162e4]

.check_preemption_disabled+0x134/0x150

quoted

[   67.701238] [c0000007d25b76e0] [c0000000007b63ac]

.powernv_cpufreq_throttle_check+0x2c/0x710

quoted

[   67.701322] [c0000007d25b7790] [c0000000007b6d18]

.powernv_cpufreq_target_index+0x288/0x360

quoted

[   67.701407] [c0000007d25b7870] [c0000000007acee4]

.__cpufreq_driver_target+0x394/0x8c0

quoted

[   67.701491] [c0000007d25b7920] [c0000000007b22ac]

.cpufreq_set+0x7c/0xd0

quoted

[   67.701565] [c0000007d25b79b0] [c0000000007adf50]

.store_scaling_setspeed+0x80/0xc0

quoted

[   67.701650] [c0000007d25b7a40] [c0000000007ae270] .store+0xa0/0x100
[   67.701723] [c0000007d25b7ae0] [c0000000003566e8]

.sysfs_kf_write+0x88/0xb0

quoted

[   67.701796] [c0000007d25b7b70] [c0000000003553b8]

.kernfs_fop_write+0x178/0x260

quoted

[   67.701881] [c0000007d25b7c10] [c0000000002ac3cc]

.__vfs_write+0x3c/0x1c0

quoted

[   67.701954] [c0000007d25b7cf0] [c0000000002ad584]

.vfs_write+0xc4/0x230

quoted

[   67.702027] [c0000007d25b7d90] [c0000000002aeef8]

.SyS_write+0x58/0x100

quoted

[   67.702101] [c0000007d25b7e30] [c00000000000bfec]

system_call+0x38/0xfc

quoted

Signed-off-by: Denis Kirjanov <kda@linux-powerpc.org <javascript:;>>

Thanks for looking into this!

quoted

---
 drivers/cpufreq/powernv-cpufreq.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/cpufreq/powernv-cpufreq.c

b/drivers/cpufreq/powernv-cpufreq.c

quoted

index d3ffde8..4cd91a3 100644

--- a/drivers/cpufreq/powernv-cpufreq.c
+++ b/drivers/cpufreq/powernv-cpufreq.c

@@ -475,7 +475,7 @@ static inline unsigned int get_nominal_index(void)
 static void powernv_cpufreq_throttle_check(void *data)

The powernv_cpufreq_throttle_check() checks if the frequency on any of
the CPUs on this chip has been throttled. Hence it needs to be
executed without preemption on a CPU on the particular chip.

It is called in two places currently:

a) powernv_cpufreq_work_fn where
it is called via smp_call_function_any() which will ensure that the
function will be executed without preempted.

b) from powernv_cpufreq_target_index: Here it should be nested within
the preempt_disable() preempt_enable() calls. It currently is not.

So, I would suggest fixing b) instead of locally fixing
smp_processor_id() to get_cpu()/put_cpu().

Ok, I'll send the v2 then.

Thanks!

quoted

 {
      struct chip *chip;
-     unsigned int cpu = smp_processor_id();
+     int cpu;
      unsigned long pmsr;
      int pmsr_pmax;
      unsigned int pmsr_pmax_idx;

@@ -491,9 +491,11 @@ static void powernv_cpufreq_throttle_check(void

*data)

quoted

                      goto next;
              chip->throttled = true;
              if (pmsr_pmax_idx > powernv_pstate_info.nominal) {
+                     cpu = get_cpu();
                      pr_warn_once("CPU %d on Chip %u has Pmax(%d)

reduced below nominal frequency(%d)\n",

quoted

                                   cpu, chip->id, pmsr_pmax,
                                   idx_to_pstate(powernv_pstate_

info.nominal));

quoted

+                     put_cpu();
                      chip->throttle_sub_turbo++;
              } else {
                      chip->throttle_turbo++;
--
1.8.3.1

--
Thanks and Regards
gautham.

-- 
Regards / Mit besten Grüßen,
Denis