linux-kernel - Re: rtc_cmos oops in cmos_rtc

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Date:	Tue, 22 Sep 2009 12:40:41 +0200
From:	Alessandro Zummo <alessandro.zummo@...ertech.it>
To:	Herton Ronaldo Krzesinski <herton@...driva.com.br>
Cc:	linux-kernel@...r.kernel.org, David Brownell <david-b@...bell.net>,
	rtc-linux@...glegroups.com
Subject: Re: rtc_cmos oops in cmos_rtc_ioctl

On Mon, 21 Sep 2009 15:53:38 -0300
Herton Ronaldo Krzesinski <herton@...driva.com.br> wrote:

> The problem here is the rtc char device being created early and acessible before
> rtc_cmos does dev_set_drvdata(dev, &cmos_rtc), so dev_get_drvdata in
> cmos_rtc_ioctl can return null, like in this example where hwclock is run right
> after char device creation that triggers the udev rule:
> ACTION=="add", SUBSYSTEM=="rtc", RUN+="/sbin/hwclock --hctosys --rtc=/dev/%k"
> And makes the oops possible, in this case hwclock looks to open and close the
> device fast enough.

 right. the best option would be to use the new irq api that was
 introduced after the creation of rtc_cmos (and thus remove the whole
 ioctl routine).

 [...]

> But I saw another issue: looks it could be possible that as cmos_rtc_ioctl
> (ioctl) can be run before rtc_device_register returns, the following call chain
> could happen in current code:
> cmos_rtc_ioctl->cmos_irq_{en,dis}able->cmos_checkintr->rtc_update_irq
> rtc_update_irq uses cmos->rtc, which is set only at return of
> rtc_device_register, and here we may have another problem... is it
> possible?

 this shouldn't happen, irqs are enabled only after everything
 has been setup to handle them.

 

-- 

 Best regards,

 Alessandro Zummo,
  Tower Technologies - Torino, Italy

  http://www.towertech.it

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