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SubjectRe: rtc ds3232 call trace in kernel
On 18/04/2016 at 06:15:40 +0000, Qianyu Gong wrote :
> Hi Akinobu,
>
> I got an rtc call trace when booting 4.6 kernel on our board and I found it
> was caused by this patch:
>
> commit fc1dcb0b39dbb10d3290f2fcd6e154670f699166
> Author: Akinobu Mita <akinobu.mita@gmail.com>
> Date: Mon Mar 7 00:27:53 2016 +0900
>
> rtc: ds3232: use rtc->ops_lock to protect alarm operations
>
> ds3232->mutex is used to protect for alarm operations which
> need to access status and control registers.
>
> But we can use rtc->ops_lock instead. rtc->ops_lock is held when most
> of rtc_class_ops methods are called, so we only need to explicitly
> acquire it from irq handler in order to protect form concurrent
> accesses.
>
> Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
> Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com
>
> The problem is that rtc->ops_lock would be accessed in ds3232_irq()
> without being initialized as rtc_device_register() is called too late.
>
> As I'm not familiar with rtc things, could I just revert the patch or you already
> have a solution to this problem? Thanks in advance.
>
>

Well, many RTC drivers actually suffer from that. I'm planning to change
the infrastructure to handle this case better.
Meanwhile, this is worth fixing.


--
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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