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

On Monday, November 7, 2016, Gautham R Shenoy [off-list ref]
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

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

quoted

    [   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

quoted

    [   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:;>>

v2:  wrap powernv_cpufreq_throttle_check()
as suggested by Gautham R Shenoy

Looks good otherwise.

Reviewed-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com <javascript:;>>

quoted

---
 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

quoted

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,

quoted

      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