From: "Rafael J. Wysocki" <rjw@sisk.pl>
To: Rudolf Marek <r.marek@assembler.cz>
Subject: Re: broken suspend [Was: 2.6.24-rc2-mm1]
Date: Mon, 19 Nov 2007 22:53:40 +0100
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Cc: Alan Stern <stern@rowland.harvard.edu>, Jiri Slaby <jirislaby@gmail.com>,
       Andrew Morton <akpm@linux-foundation.org>, Greg KH <greg@kroah.com>,
       Kernel development list <linux-kernel@vger.kernel.org>,
       Linux-pm mailing list <linux-pm@lists.linux-foundation.org>,
       lm-sensors@lm-sensors.org
References: <Pine.LNX.4.44L0.0711182156330.22727-100000@netrider.rowland.org> <4741EB91.9080000@assembler.cz>
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On Monday, 19 of November 2007, Rudolf Marek wrote:
> 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

Well, in principle you can use the observation that the _FROZEN versions
are used during suspend/hibernation.  Thus, if you only unregister the device
for CPU_DEAD, but you won't do that for CPU_DEAD_FROZEN, it will work as long
as the freezer is there.

> > 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).

In fact, it's already done that way and I don't think it's racy (see above).

Greetings,
Rafael
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