linux-kernel - Re: rtc ds3232 call trace in kernel

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Date:	Tue, 19 Apr 2016 12:58:03 +0900
From:	Akinobu Mita <akinobu.mita@...il.com>
To:	Qianyu Gong <qianyu.gong@....com>
Cc:	"alexandre.belloni@...e-electrons.com" 
	<alexandre.belloni@...e-electrons.com>,
	Mingkai Hu <mingkai.hu@....com>,
	"rtc-linux@...glegroups.com" <rtc-linux@...glegroups.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: rtc ds3232 call trace in kernel

2016-04-19 11:36 GMT+09:00 Qianyu Gong <qianyu.gong@....com>:
>
>> -----Original Message-----
>> From: Akinobu Mita [mailto:akinobu.mita@...il.com]
>> Sent: Monday, April 18, 2016 9:02 PM
>> To: Qianyu Gong <qianyu.gong@....com>
>> Cc: alexandre.belloni@...e-electrons.com; Mingkai Hu <mingkai.hu@....com>;
>> rtc-linux@...glegroups.com; linux-kernel@...r.kernel.org
>> Subject: Re: rtc ds3232 call trace in kernel
>>
>> 2016-04-18 15:15 GMT+09:00 Qianyu Gong <qianyu.gong@....com>:
>> > 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@...il.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@...il.com>
>> >
>> > Signed-off-by: Alexandre Belloni <alexandre.belloni@...e-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.
>>
>> You have already identified the root cause of this issue.
>>
>> > 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.
>>
>> Could you check if the problem is resolved by moving the call of
>> devm_rtc_device_register() from the end of ds3232_probe() to just before
>> registering irq handler?
>
> Yes. It works(no call trace now).

Thanks for testing.  Do you mind submitting your patch to
rtc-linux@...glegroups.com ?