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

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Date:	Tue, 19 Apr 2016 04:11:30 +0000
From:	Qianyu Gong <qianyu.gong@....com>
To:	Akinobu Mita <akinobu.mita@...il.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

> -----Original Message-----
> From: Akinobu Mita [mailto:akinobu.mita@...il.com]
> Sent: Tuesday, April 19, 2016 11:58 AM
> 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
> 
> 2016-04-19 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 ?

No problem.:)

Regards,
Qianyu