linux-kernel - Re: [PATCH 1/2] [CPUFREQ] powernow-k8: Don't notify of successful transition if we failed.

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Message-ID: <20110616142440.GA5576@dumpdata.com>
Date:	Thu, 16 Jun 2011 10:24:40 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Borislav Petkov <bp@...en8.de>, linux-kernel@...r.kernel.org,
	davej@...hat.com, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, x86@...nel.org, cpufreq@...r.kernel.org,
	andre.przywara@....com, Mark.Langsdorf@....com
Subject: Re: [PATCH 1/2] [CPUFREQ] powernow-k8: Don't notify of successful
 transition if we failed.

On Wed, Jun 15, 2011 at 06:26:08PM -0400, Konrad Rzeszutek Wilk wrote:
> > > @@ -1112,6 +1114,9 @@ static int transition_frequency_pstate(struct powernow_k8_data *data,
> > >  	}
> > >  
> > >  	res = transition_pstate(data, pstate);
> > > +	if (res)
> > > +		return res;
> > 
> > That's wrong because transition_pstate() returns 0 unconditionally
> > (at least it does so on 3.0-rc3). But this change accidentally fixes
> > a different bug because res is used uninitialized, containing stack
> > garbage otherwise.
> > 
> > A proper fix should be to check against data->max_hw_pstate and
> > check whether the entry is not CPUFREQ_ENTRY_INVALID (look at
> > fill_powernow_table_pstate() for example).
> 
> Aha! I can respin a patch for that tomorrow.

I divided it in two patches - so that the Reported/Tested-by tag is on
the translate_vid patch with its full glory of explanation. The
pstate checking is removed.

Will post the other patch under a different subject.

>From 3ae9a2094d893ab1a500833a48cb29e0f1c81ed8 Mon Sep 17 00:00:00 2001
From: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Date: Thu, 16 Jun 2011 09:02:57 -0400
Subject: [PATCH 1/2] [CPUFREQ] powernow-k8: Don't notify of successful
 transition if we failed (vid case).

Before this patch if we failed the vid transition would still try to
submit the "new" frequencies to cpufreq.
That is incorrect - also we could submit a non-existing frequency value
which would cause cpufreq to crash. The ultimate fix is in cpufreq
to deal with incorrect values, but this patch improves the error
recovery in the AMD powernowk8 driver.

The failure that was reported was as follow:

powernow-k8: Found 1 AMD Athlon(tm) 64 Processor 3700+ (1 cpu cores) (version 2.20.00)
powernow-k8: fid 0x2 (1000 MHz), vid 0x12
powernow-k8: fid 0xa (1800 MHz), vid 0xa
powernow-k8: fid 0xc (2000 MHz), vid 0x8
powernow-k8: fid 0xe (2200 MHz), vid 0x8
Marking TSC unstable due to cpufreq changes
powernow-k8: fid trans failed, fid 0x2, curr 0x0
BUG: unable to handle kernel paging request at ffff880807e07b78
IP: [<ffffffff81479163>] cpufreq_stats_update+0x46/0x5b
...

And transition fails and data->currfid ends up with 0. Since
the machine does not support 800Mhz value when the calculation is
done ('find_khz_freq_from_fid(data->currfid);') it reports the
new frequency as 800000 which is bogus. This patch fixes
the issue during target setting.

The patch however does not fix the issue in 'powernowk8_cpu_init'
where the pol->cur can also be set with the 800000 value:

          pol->cur = find_khz_freq_from_fid(data->currfid);
  dprintk("policy current frequency %d kHz\n", pol->cur);

  /* min/max the cpu is capable of */
  if (cpufreq_frequency_table_cpuinfo(pol, data->powernow_table)) {

The fix for that looks to update cpufreq_frequency_table_cpuinfo to
check pol->cur.... but that would cause an regression in how the
acpi-cpufreq driver works (it sets cpu->cur after calling
cpufreq_frequency_table_cpuinfo). Instead the fix will be to let
cpufreq gracefully handle bogus data (another patch).

CC: Borislav Petkov <bp@...en8.de>
CC: andre.przywara@....com
CC: Mark.Langsdorf@....com
Reported-by: Tobias Diedrich <ranma+xen@...edrich.de>
Tested-by: Tobias Diedrich <ranma+xen@...edrich.de>
[v1: Rebased on v3.0-rc2, reduced patch to deal with vid case]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
---
 drivers/cpufreq/powernow-k8.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/drivers/cpufreq/powernow-k8.c b/drivers/cpufreq/powernow-k8.c
index 83479b6..fe53572 100644
--- a/drivers/cpufreq/powernow-k8.c
+++ b/drivers/cpufreq/powernow-k8.c
@@ -1079,6 +1079,8 @@ static int transition_frequency_fidvid(struct powernow_k8_data *data,
 	}

 	res = transition_fid_vid(data, fid, vid);
+	if (res)
+		return res;
 	freqs.new = find_khz_freq_from_fid(data->currfid);

 	for_each_cpu(i, data->available_cores) {
-- 
1.7.5.4

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