linux-kernel - Re: Regression on cpufreq in v3.12-rc1

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Message-ID: <45987104.t6r4hvPgQn@vostro.rjw.lan>
Date:	Thu, 19 Sep 2013 00:41:09 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	srivatsa.bhat@...ux.vnet.ibm.com
Subject: Re: Regression on cpufreq in v3.12-rc1

On Wednesday, September 18, 2013 11:21:45 PM Linus Walleij wrote:
> Hi Rafael, Viresh,
> 
> I'm seeing this problem and maybe you can help me out fixing it
> properly:
> 
> On some machines like the StrongARM SA1100 it seems that
> cpufreq_get() can be called before the cpufreq driver and thus the
> policy is set, resulting in a crash like this:

Did you try the current linux-next branch from my tree?

Rafael


> .------------[ cut here ]------------
> .kernel BUG at /home/linus/linux/drivers/cpufreq/cpufreq.c:80!
> .Internal error: Oops - BUG: 0 [#1] ARM
> .Modules linked in:
> .CPU: 0 PID: 1 Comm: swapper Not tainted 3.12.0-rc1-00001-g1266dae-dirty #17
> .task: c1830000 ti: c1832000 task.ti: c1832000
> (...)
> Backtrace:
> [<c01ea1a4>] (lock_policy_rwsem_read+0x0/0x48) from [<c01eb5c8>]
> (cpufreq_get+0x34/0x68)
> [<c01eb594>] (cpufreq_get+0x0/0x68) from [<c0185908>]
> (sa1100fb_activate_var+0xdc/0x3ac)
>  r5:00000003 r4:0000000a
> [<c018582c>] (sa1100fb_activate_var+0x0/0x3ac) from [<c0185c78>]
> (sa1100fb_set_par+0xa0/0xa8)
> [<c0185bd8>] (sa1100fb_set_par+0x0/0xa8) from [<c0180418>]
> (fbcon_init+0x444/0x4a8)
>  r4:c1803200
> [<c017ffd4>] (fbcon_init+0x0/0x4a8) from [<c019a8b4>] (visual_init+0x78/0xc8)
> [<c019a83c>] (visual_init+0x0/0xc8) from [<c01a0010>]
> (do_bind_con_driver+0x160/0x310)
> 
> This bug comes from the framebuffer but I first encountered it
> in the PCMCIA driver, and both seem to cause the bug.
> 
> In the past I think things worked smoothly: the consumers
> calling cpufreq_get() too early would just get 0 back.
> (Or so it seems to me.)
> 
> The BUG() statement causing it is in the lock_policy_rwsem_##mode(int cpu)
> macro.
> 
> Applying a patch like this seems to fix the issue:
> 
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 43c24aa..4977b4b 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -70,7 +70,8 @@ static DEFINE_PER_CPU(struct rw_semaphore, cpu_policy_rwsem);
>  static int lock_policy_rwsem_##mode(int cpu)                           \
>  {                                                                      \
>         struct cpufreq_policy *policy = per_cpu(cpufreq_cpu_data, cpu); \
> -       BUG_ON(!policy);                                                \
> +       if(!policy)                                                     \
> +               return 0;                                               \
>         down_##mode(&per_cpu(cpu_policy_rwsem, policy->cpu));           \
>                                                                         \
>         return 0;                                                       \
> @@ -83,7 +84,8 @@ lock_policy_rwsem(write, cpu);
>  static void unlock_policy_rwsem_##mode(int cpu)
>          \
>  {                                                                      \
>         struct cpufreq_policy *policy = per_cpu(cpufreq_cpu_data, cpu); \
> -       BUG_ON(!policy);                                                \
> +       if(!policy)                                                     \
> +               return;                                                 \
>         up_##mode(&per_cpu(cpu_policy_rwsem, policy->cpu));             \
>  }
> 
> @@ -1423,6 +1425,9 @@ static unsigned int __cpufreq_get(unsigned int cpu)
>         struct cpufreq_policy *policy = per_cpu(cpufreq_cpu_data, cpu);
>         unsigned int ret_freq = 0;
> 
> +       if (!policy)
> +               return ret_freq;
> +
>         if (!cpufreq_driver->get)
>                 return ret_freq;
> 
> I don't really know if this is the right solution at all, so please
> help me out here... if you want that patch I can send it once
> I understand this properly.
> 
> Yours,
> Linus Walleij
-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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