da9063 - Reboot issue : koops rcu_note_context_switch

[Köry Maincent]

More readable with quote character sorry for the duplicate.


Hi Hariprasad,

> Hi Kory Maincent.
> 
> On Tue, 26 Mar 2019 at 13:21, Köry Maincent <kory.maincent at navocap.com 
> <mailto:kory.maincent at navocap.com>> wrote:
> 
> >    Hello,
> >
> >    I got a kernel warning on the reboot of my embedded board, and
> >    sometimes I got stuck in the reboot.
> >    I work on the IMX6Q with a PMIC da9063 and the last kernel release.
> >
> >    It happens in the /da9063_wdt_restart/ function at the
> >    /regmap_write/ call in the CONTROL_F register.
> >    (drivers/watchdog/da9063_wdt.c)
> 
> 
>  From trace we are able figure out the flow,
> 
> reboot
> |
> |
> invokes system call(sys_reboot)
> |
> |
>   watchdog_restart)notifier
> |
> |
> da9063_wdt_restart
> |
> |
> It sending I2c rear/write commands.
> 
> Is this expected behaviour  ??

Yes it is.

> If I access to other register in that function, I don't have this issue.
> The reason could be ,you are accessing other registers directly not 
> through I2C.
I was wrong on this point, because of bad order debug printing in the 
drivers.


I manage to avoid the issue with a hotfix : adding rcu_read_unlock(); 
before I2C writing in the da9063_wdt_restart function. There is no more 
koops warning neither freezing reboot.
I don't think it is a clean patch and I don't understand the relation to 
preemption.
It may happens because of an RCU critical section not closed?


Regards Kory.