linux-kernel - Re: kernfs/rtc: circular dependency between kernfs and ops

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Message-ID: <20140325233936.655a798e@linux.lan.towertech.it>
Date:	Tue, 25 Mar 2014 23:39:36 +0100
From:	Alessandro Zummo <a.zummo@...ertech.it>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	Tejun Heo <tj@...nel.org>, Greg KH <greg@...ah.com>,
	rtc-linux@...glegroups.com, LKML <linux-kernel@...r.kernel.org>
Subject: Re: kernfs/rtc: circular dependency between kernfs and ops_lock

On Tue, 25 Mar 2014 17:52:30 -0400
Sasha Levin <sasha.levin@...cle.com> wrote:

> >
> >   Pretty interesting indeed. One option would be to remove
> >   the sys files before acquiring the lock. But I wonder
> >   if this could lead to other issues.
> >  
> 
> Ping? Seems this thing got lost.

 What if we move

   rtc_sysfs_del_device(rtc);

 before acquiring the lock?

diff --git a/drivers/rtc/class.c b/drivers/rtc/class.c
index 589351e..a0c19a3 100644
--- a/drivers/rtc/class.c
+++ b/drivers/rtc/class.c
@@ -261,11 +261,13 @@ EXPORT_SYMBOL_GPL(rtc_device_register);
 void rtc_device_unregister(struct rtc_device *rtc)
 {
        if (get_device(&rtc->dev) != NULL) {
+
+               rtc_sysfs_del_device(rtc);
+
                mutex_lock(&rtc->ops_lock);
                /* remove innards of this RTC, then disable it, before
                 * letting any rtc_class_open() users access it again
                 */
-               rtc_sysfs_del_device(rtc);
                rtc_dev_del_device(rtc);
                rtc_proc_del_device(rtc);
                device_unregister(&rtc->dev);


-- 

 Best regards,

 Alessandro Zummo,
  Tower Technologies - Torino, Italy

  http://www.towertech.it

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