uevent / call_usermoderrelated breakage on suspend to disk [Was: Re: PCMCIA-related breakage on suspend to disk]

[Dominik Brodowski]

Hi,

On Thu, Nov 24, 2005 at 05:29:08AM +0000, Matthew Garrett wrote:
> In the Ubuntu suspend to disk script, we eject all PCMCIA cards before 
> suspend in order to minimise problems caused by drivers that aren't 
> terribly happy with being suspended. This seems to cause the following 
> issue:
> 
> 1) Userspace ejects the card
> 2) Userspace triggers suspend to disk
> 3) Userspace is frozen
> 4) The kernel suspends all hardware
> 5) An atomic copy of memory is made
> 6) The kernel resumes the hardware in order to write the image to disk
> 7) socket_resume is called
> 8) socket_resume calls socket_insert
> 9) The machine hangs
> 
> It's fairly clear /why/ socket_insert is called - it's possible that a 
> card has been inserted between suspend and resume (we call cardctl 
> insert from userspace in order to deal with this case). However, it 
> seems to cause problems in this specific case, and I don't understand 
> why. The following patch avoids the issue, but plainly isn't the correct 
> solution.

No, it doesn't seem so...

The actual hang appears in this call trace (many functions left out...)

drivers/pcmcia/cs.c:	socket_resume
drivers/pcmcia/cs.c:	socket_insert
drivers/pcmcia/cs.c:	pcmcia_device_add
drivers/base/core.c:	device_register
drivers/base/core.c:	device_add
		(additional info:
			if ((error = device_pm_add(dev)))
		 is never reached, as the pr_debug() didn't show up...)
lib/kobject_uevent.c:	kobject_hotplug

	pr_debug ("%s: %s %s seq=%llu %s %s %s %s %s\n",
		  __FUNCTION__, argv[0], argv[1], (unsigned long long)seq,
		  envp[0], envp[1], envp[2], envp[3], envp[4]);

	is still shown, it then hangs either in

--->	send_uevent(action_string, kobj_path, envp, GFP_KERNEL);

	or

--->	retval = call_usermodehelper (argv[0], argv, envp, 0);


What to do?
a) fix send_uevent or call_usermodehelper to not lock up in the
	resume-when-suspending-to-disk-path
b) make device_add fail if in
	resume-when-suspending-to-disk-path
c) disable device-adding in drivers/pcmcia/cs.c:socket_resume() if in
	resume-when-suspending-to-disk-path

Thanks,
	Dominik