linux-kernel - Re: [PATCH] cpufreq: arm_big_little: fix frequency check when bL switcher is active

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Wed, 14 Oct 2015 08:12:00 +0100
From:	"Jon Medhurst (Tixy)" <tixy@...aro.org>
To:	Sudeep Holla <sudeep.holla@....com>
Cc:	Viresh Kumar <viresh.kumar@...aro.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cpufreq: arm_big_little: fix frequency check when bL
 switcher is active

On Tue, 2015-10-13 at 11:36 +0100, Sudeep Holla wrote:
> 
> On 13/10/15 08:19, Jon Medhurst (Tixy) wrote:
[...]
> > But then we wouldn't get the WARN_ON and pr_err triggered when we detect
> > the clock rate isn't set, which surely is half the reason for the check
> > in the first place?
> >
> 
> Not sure if I understand what you mean or may be I was not clear, so
> thought I will put the delta here. Let me know if and how its still a 
> problem.
>
> diff --git i/drivers/cpufreq/arm_big_little.c 
> w/drivers/cpufreq/arm_big_little.c
> index f1e42f8ce0fc..05e850f80f39 100644
> --- i/drivers/cpufreq/arm_big_little.c
> +++ w/drivers/cpufreq/arm_big_little.c
> @@ -164,6 +164,16 @@ bL_cpufreq_set_rate(u32 cpu, u32 old_cluster, u32 
> new_cluster, u32 rate)
> 
>          mutex_unlock(&cluster_lock[new_cluster]);
> 
> +       /*
> +        * FIXME: clk_set_rate has to handle the case where clk_change_rate
> +        * can fail due to hardware or firmware issues. Until the clk core
> +        * layer is fixed, we can check here. In most of the cases we will
> +        * be reading only the cached value anyway. This needs to  be 
> removed
> +        * once clk core is fixed.
> +        */
> +       if (bL_cpufreq_get_rate(cpu) != new_rate)
> +               return -EIO;
> +
>          /* Recalc freq for old cluster when switching clusters */
>          if (old_cluster != new_cluster) {
>                  pr_debug("%s: cpu: %d, old cluster: %d, new cluster: %d\n",

That's what I though you meant, and I can't see why you would want to do
that and bypass the error reporting for clk_get_rate failing. After all,
the code we're moving around is explicitly there to workaround the fact
that clk_set_rate doesn't actually pass through all errors, so it's
doing additional error checking. (At least, that's what the comment
says). So this looks more logical to me.

ret = clk_set_rate()
if(!ret)                         /* if no error from clk_set_rate   */
    if(clk_get_rate()!=correct)  /* but some additional checks fail */
        ret = -EIO;              /* then indicate an error anyway   */

if (WARN_ON(ret))                /* Warn if error setting rate and */
    pr_err("clk_set_rate failed")/* print and error too */


But if people want the if(clk_get_rate()!=correct) after the WARN_ON
then lets do that, the important thing is to get the code fixed.

-- 
Tixy

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/