On Thursday, June 01, 2017 01:08:16 AM Jongman Heo wrote:

quoted

--------- Original Message ---------
Sender : Rafael J. Wysocki [off-list ref]
Date   : 2017-06-01 08:58 (GMT+9)
Title  : Re: FW: [4.12 regression] "cpufreq: intel_pstate: Active mode P-state limits rework"

On Monday, May 29, 2017 02:18:52 AM Jongman Heo wrote:

quoted

Hi,

FYI, 4.12-rc3 still has this issue.

 
--------- Original Message ---------
Sender : 허종만 [off-list ref]
Date   : 2017-05-16 13:25 (GMT+9)
Title  : [4.12 regression] "cpufreq: intel_pstate: Active mode P-state limits rework"
 
 
Hi,
 
With 4.12-rc1 (Linus git), booting fails due to kernel panic, at intel_pstate_register_driver+0x56/0x110.
I can't copy the whole trace from the graphic console, it looks like below.
 
Call Trace:
  intel_pstate_init
  intel_pstate_setup
  do_one_initcall
  set_debug_rodata
  kernel_init_freeable
  rest_init
  kernel_init
  ret_from_fork
    Code: ...
  RIP: intel_pstate_register_driver+0x56/0x110 RSP: ffffa3a98000bd80
  ...

I guess this is a division by 0 due to the unmet assumption that the denominator
in min_perf_pct_min() will always be nonzero.

If this guess is correct, the patch below should help, so can you please test it?

Thanks,
Rafael


---
drivers/cpufreq/intel_pstate.c |    5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

Index: linux-pm/drivers/cpufreq/intel_pstate.c
===================================================================

--- linux-pm.orig/drivers/cpufreq/intel_pstate.c
+++ linux-pm/drivers/cpufreq/intel_pstate.c

@@ -571,9 +571,10 @@ static inline void update_turbo_state(vo

static int min_perf_pct_min(void)
{
        struct cpudata *cpu = all_cpu_data[0];
+        int turbo_pstate = cpu->pstate.turbo_pstate;

-        return DIV_ROUND_UP(cpu->pstate.min_pstate * 100,
-                            cpu->pstate.turbo_pstate);
+        return turbo_pstate ?
+                DIV_ROUND_UP(cpu->pstate.min_pstate * 100, turbo_pstate) : 0;
}

static s16 intel_pstate_get_epb(struct cpudata *cpu_data)

Hi,

Your patch fixes the issue.

OK, thanks for the confirmation.

Here it goes again with a changelog and all.

---
From: Rafael J. Wysocki <redacted>
Subject: [PATCH] cpufreq: intel_pstate: Avoid division by 0 in min_perf_pct_min()

Commit c5a2ee7dde89 (cpufreq: intel_pstate: Active mode P-state
limits rework) incorrectly assumed that pstate.turbo_pstate will
always be nonzero for CPU0 in min_perf_pct_min() if
cpufreq_register_driver() has succeeded which may not be the case
in virtualized environments.

If that is not the case, it leads to an early crash on boot in
intel_pstate_register_driver(), so add a sanity check to
min_perf_pct_min() to prevent the crash from happening.

Fixes: c5a2ee7dde89 (cpufreq: intel_pstate: Active mode P-state limits rework)
Reported-and-tested-by: Jongman Heo <redacted>
Signed-off-by: Rafael J. Wysocki <redacted>
---
 drivers/cpufreq/intel_pstate.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

Index: linux-pm/drivers/cpufreq/intel_pstate.c
===================================================================

--- linux-pm.orig/drivers/cpufreq/intel_pstate.c
+++ linux-pm/drivers/cpufreq/intel_pstate.c

@@ -571,9 +571,10 @@ static inline void update_turbo_state(vo
 static int min_perf_pct_min(void)
 {
 	struct cpudata *cpu = all_cpu_data[0];
+	int turbo_pstate = cpu->pstate.turbo_pstate;
 
-	return DIV_ROUND_UP(cpu->pstate.min_pstate * 100,
-			    cpu->pstate.turbo_pstate);
+	return turbo_pstate ?
+		DIV_ROUND_UP(cpu->pstate.min_pstate * 100, turbo_pstate) : 0;
 }
 
 static s16 intel_pstate_get_epb(struct cpudata *cpu_data)