linux-kernel - Re: broken suspend [Was: 2.6.24-rc2-mm1]

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Date:	Mon, 19 Nov 2007 21:01:21 +0100
From:	Rudolf Marek <r.marek@...embler.cz>
To:	Alan Stern <stern@...land.harvard.edu>
CC:	Jiri Slaby <jirislaby@...il.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg KH <greg@...ah.com>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	Linux-pm mailing list <linux-pm@...ts.linux-foundation.org>,
	lm-sensors@...sensors.org, "Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: broken suspend [Was: 2.6.24-rc2-mm1]

Hello all,
>>> gives coretemp_cpu_callback -> coretemp_device_remove ->
>>> platform_device_unregister, so coretemp seems to be what I have and you don't.
> 
> Yes.
> 
> For the coretemp developers: coretemp_cpu_callback() needs to be more 
> careful about what it does.  During a system sleep transition (suspend, 
> hibernate, resume) it isn't possible to register or unregister a 
> device.  Attempts to register will fail and attempts to unregister will 
> block until the system sleep is over -- and for this callback that 
> means hanging.

Well I wrote the driver. Thanks for the clarification. If I recall correctly I 
looked how this part should be done from others drivers. Now while checking
what happened to the file, seems Rafael added something related.

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=8bb7844286fb8c9fce6f65d8288aeb09d03a5e0d

> It's not clear what the best way is to fix this.  Perhaps the CPU 
> notification should be sent along with a special flag indicating that 
> the CPU transition is part of a system sleep (although this seems 
> racy).  Perhaps the driver should notice when a system sleep begins, 
> and defer all CPU-change handling until after the sleep is over.

maybe it does exist?  CPU_DOWN_PREPARE ?

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=Documentation/cpu-hotplug.txt;hb=HEAD

Unfortunately I'm not very familiar with this, calling the 
coretemp_device_remove from CPU_DOWN_PREPARE would help? Looking at microcode 
driver, seems it just hide sysfs interface from user.

Thanks,
Rudolf
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