Re: [PATCH 9/9] ARM: tegra: fix sleeping while atomic in CPU idle

From: Jon Hunter <jonathanh-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
To: "Michał Mirosław" <mirq-linux-CoA6ZxLDdyEEUmgCuDUIdw@public.gmane.org>
Cc: linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org
Subject: Re: [PATCH 9/9] ARM: tegra: fix sleeping while atomic in CPU idle
Date: Fri, 21 Jul 2017 09:15:31 +0100	[thread overview]
Message-ID: <bfb0fab3-da6f-44b9-dfb6-3da4f2715af0@nvidia.com> (raw)
In-Reply-To: <20170720162852.rh565t5as2tbe6np-cHozx32mtrEEUmgCuDUIdw@public.gmane.org>

On 20/07/17 17:28, Michał Mirosław wrote:
> On Thu, Jul 20, 2017 at 01:45:12PM +0100, Jon Hunter wrote:
>>
>> On 20/07/17 01:29, Michał Mirosław wrote:
>>> This removes unnecessary lock causing following BUG splat:
>>>
>>> BUG: sleeping function called from invalid context at /linux/kernel/locking/mutex.c:747
>>> in_atomic(): 1, irqs_disabled(): 128, pid: 0, name: swapper/0
>>> no locks held by swapper/0/0.
>>> CPU: 0 PID: 0 Comm: swapper/0 Tainted: G        W 4.13.0-rc1mq-00016-gbf3f627c6b2b #1
>>> Hardware name: NVIDIA Tegra SoC (Flattened Device Tree)
>>> [<b0110a14>] (unwind_backtrace) from [<b010c710>] (show_stack+0x18/0x1c)
>>> [<b010c710>] (show_stack) from [<b068ada8>] (dump_stack+0x84/0x98)
>>> [<b068ada8>] (dump_stack) from [<b014ff54>] (___might_sleep+0x158/0x17c)
>>> [<b014ff54>] (___might_sleep) from [<b06a15c4>] (__mutex_lock+0x34/0x9a0)
>>> [<b06a15c4>] (__mutex_lock) from [<b06a30dc>] (mutex_lock_nested+0x24/0x2c)
>>> [<b06a30dc>] (mutex_lock_nested) from [<b041f6d8>] (tegra_powergate_is_powered+0x40/0xa4)
>>> [<b041f6d8>] (tegra_powergate_is_powered) from [<b04197e8>] (tegra30_cpu_rail_off_ready+0x28/0x6c)
>>> [<b04197e8>] (tegra30_cpu_rail_off_ready) from [<b011c73c>] (tegra30_idle_lp2+0x70/0x114)
>>> [<b011c73c>] (tegra30_idle_lp2) from [<b0516080>] (cpuidle_enter_state+0x12c/0x47c)
>>> [<b0516080>] (cpuidle_enter_state) from [<b0163394>] (do_idle+0x1b4/0x204)
>>> [<b0163394>] (do_idle) from [<b016368c>] (cpu_startup_entry+0x20/0x24)
>>> [<b016368c>] (cpu_startup_entry) from [<b0900dd8>] (start_kernel+0x39c/0x3a8)
>>>
>>> Signed-off-by: Michał Mirosław <mirq-linux-CoA6ZxLDdyEEUmgCuDUIdw@public.gmane.org>
>>> ---
>>>  drivers/soc/tegra/pmc.c | 2 --
>>>  1 file changed, 2 deletions(-)
>>>
>>> diff --git a/drivers/soc/tegra/pmc.c b/drivers/soc/tegra/pmc.c
>>> index e233dd5dcab3..3e6ec9fdba41 100644
>>> --- a/drivers/soc/tegra/pmc.c
>>> +++ b/drivers/soc/tegra/pmc.c
>>> @@ -526,9 +526,7 @@ int tegra_powergate_is_powered(unsigned int id)
>>>  	if (!tegra_powergate_is_valid(id))
>>>  		return -EINVAL;
>>>  
>>> -	mutex_lock(&pmc->powergates_lock);
>>>  	status = tegra_powergate_state(id);
>>> -	mutex_unlock(&pmc->powergates_lock);
>>>  
>>>  	return status;
>>>  }
>>
>> Thanks for the fix. However, I would prefer that we fix this the following
>> way ...
>>
>> diff --git a/drivers/clk/tegra/clk-tegra30.c b/drivers/clk/tegra/clk-tegra30.c
>> index a2d163f759b4..546d2b121c39 100644
>> --- a/drivers/clk/tegra/clk-tegra30.c
>> +++ b/drivers/clk/tegra/clk-tegra30.c
>> @@ -1152,9 +1152,9 @@ static bool tegra30_cpu_rail_off_ready(void)
>>  
>>         cpu_rst_status = readl(clk_base +
>>                                 TEGRA30_CLK_RST_CONTROLLER_CPU_CMPLX_STATUS);
>> -       cpu_pwr_status = tegra_powergate_is_powered(TEGRA_POWERGATE_CPU1) ||
>> -                        tegra_powergate_is_powered(TEGRA_POWERGATE_CPU2) ||
>> -                        tegra_powergate_is_powered(TEGRA_POWERGATE_CPU3);
>> +       cpu_pwr_status = tegra_pmc_cpu_is_powered(1) ||
>> +                        tegra_pmc_cpu_is_powered(2) ||
>> +                        tegra_pmc_cpu_is_powered(3);
>>  
>>         if (((cpu_rst_status & 0xE) != 0xE) || cpu_pwr_status)
>>                 return false;
>> diff --git a/drivers/soc/tegra/pmc.c b/drivers/soc/tegra/pmc.c
>> index e233dd5dcab3..f61371ea3fe0 100644
>> --- a/drivers/soc/tegra/pmc.c
>> +++ b/drivers/soc/tegra/pmc.c
>> @@ -605,7 +605,7 @@ bool tegra_pmc_cpu_is_powered(unsigned int cpuid)
>>         if (id < 0)
>>                 return false;
>>  
>> -       return tegra_powergate_is_powered(id);
>> +       return tegra_powergate_state(id);
>>  }
>>
>>
>> Could you try the above and make sure that this works? 
> 
> Something ate TABs in your patch, but yes, it works.
> 
>> I would prefer to leave the mutex in tegra_powergate_is_powered() so it could
>> be used by any driver. Or maybe we could even get rid of
>> tegra_powergate_is_powered() if we don't really need it.
> 
> This mutex does not protect anything here, though - there is only one register
> read inside the locked section, and after unlock other CPU might change
> it before the read value gets returned.
> 
> Code size-wise it would be better to remove tegra_pmc_cpu_is_powered()
> instead.

Maybe, but tegra_pmc_cpu_is_powered() is needed by
tegra30_boot_secondary().

Jon

-- 
nvpublic