linux-kernel - Re: Crashing 'kzm' target in next-20160913 due to 'gpio: mxc: shift gpio_mxc_init() to subsys

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Date:   Thu, 15 Sep 2016 07:35:16 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
        Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>
Cc:     Shawn Guo <shawnguo@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linus Walleij <linus.walleij@...aro.org>
Subject: Re: Crashing 'kzm' target in next-20160913 due to 'gpio: mxc: shift
 gpio_mxc_init() to subsys_initcall level'

On 09/15/2016 07:23 AM, Uwe Kleine-König wrote:
> On Thu, Sep 15, 2016 at 04:35:04PM +0300, Vladimir Zapolskiy wrote:
>> Hi Guenter,
>>
>> On 09/14/2016 06:20 AM, Guenter Roeck wrote:
>>> Hi Vladimir,
>>>
>>> your commit e188cbf7564f ("gpio: mxc: shift gpio_mxc_init() to subsys_initcall level")
>>> in -next causes the following crash when running the 'kzm' target (and most likely
>>> the real thing) with qemu.
>>>
>>> [    1.211426] Unable to handle kernel NULL pointer dereference at virtual address 0000000c
>>> [    1.211600] pgd = c0004000
>>> [    1.211680] [0000000c] *pgd=00000000
>>> [    1.212067] Internal error: Oops: 5 [#1] SMP ARM
>>> [    1.212245] Modules linked in:
>>> [    1.212542] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.8.0-rc6-next-20160913 #1
>>> [    1.212671] Hardware name: Kyoto Microcomputer Co., Ltd. KZM-ARM11-01
>>> [    1.212825] task: c6848000 task.stack: c683e000
>>> [    1.213231] PC is at platform_get_irq+0xc0/0xe8
>>>
>>> See http://kerneltests.org/builders/qemu-arm-next/builds/525/steps/qemubuildcommand/logs/stdio
>>> for a complete log.
>>>
>>> Problem is quite subtle. The change causes the gpio driver to be installed later.
>>> As a result, kzm_init_smsc9118() fails to initialize the gpio pins correctly.
>>> gpio_request() in that function returns -EPROBE_DEFER, which is ignored,
>>> gpio_to_irq() then returns -22 which is unconditionally assigned as interrupt number.
>>> platform_get_irq(), as called from the smsc driver, gets this negative interrupt
>>> number, and passes it unconditionally to irq_get_irq_data(), which returns NULL.
>>> The NULL pointer is then passed to irqd_set_trigger_type() which, not entirely
>>> surprisingly, crashes.
>>>
>>> So, in other words, lots of bugs here. Nevertheless, I would suggest to keep using
>>> postcore_initcall(), at least until it is sure that all gpio clients handle -EPROBE_DEFER
>>> correctly.
>>
>> I'm inviting Shawn and Uwe to the discussion.
>>
>> The proper fix in this particular case should be like this one:
>>
>> diff --git a/arch/arm/mach-imx/mach-kzm_arm11_01.c b/arch/arm/mach-imx/mach-kzm_arm11_01.c
>> index 31df4361996f..8288acfe7221 100644
>> --- a/arch/arm/mach-imx/mach-kzm_arm11_01.c
>> +++ b/arch/arm/mach-imx/mach-kzm_arm11_01.c
>> @@ -245,13 +245,17 @@ static void __init kzm_board_init(void)
>>  	mxc_iomux_setup_multiple_pins(kzm_pins,
>>  				      ARRAY_SIZE(kzm_pins), "kzm");
>> -	kzm_init_ext_uart();
>> -	kzm_init_smsc9118();
>>  	kzm_init_imx_uart();
>>  	pr_info("Clock input source is 26MHz\n");
>>  }
>> +static void __init kzm_late_init(void)
>> +{
>> +	kzm_init_ext_uart();
>> +	kzm_init_smsc9118();
>> +}
>> +
>>  /*
>>   * This structure defines static mappings for the kzm-arm11-01 board.
>>   */
>> @@ -291,5 +295,6 @@ MACHINE_START(KZM_ARM11_01, "Kyoto Microcomputer Co., Ltd. KZM-ARM11-01")
>>  	.init_irq = mx31_init_irq,
>>  	.init_time	= kzm_timer_init,
>>  	.init_machine = kzm_board_init,
>> +	.init_late	= kzm_late_init,
>>  	.restart	= mxc_restart,
>>  MACHINE_END
>
> That + checking the return code of gpio_request and the other calls.
> Or better, convert the machine to dt.
>
>> But I agree that there might be more legacy boards (i.MX31 only IMHO),
>> which may attempt to manipulate GPIO lines before subsys_initcall()
>> level.
>
> I wouldn't revert anything for legacy boards. That's the chance to say
> in the near future: They stopped working in September 2016, obviously
> nobody cares, let's rip them. :-)
>
New kernel development philosophy ? Regressions are acceptable as long as
they affect a board older than X years ? What is your cut-off date for accepting
regressions like that ?

If that is the new philosophy, can it be made official ? That would help me
understand when I don't need to bother sending bug reports.

Following that new development paradigm, should I refrain from reporting that
arm-realview-eb-11mp-revb has been broken in -next since next-20160914 ?

Thanks,
Guenter