[Suspend2-devel] Re: [ltp] [PATCH] 2.6.17: Unload disks heads before powering down

[Henrique de Moraes Holschuh]

On Wed, 27 Sep 2006, Nigel Cunningham wrote:
> > > Now, teaching the kernel how to differentiate a "regular" scsi bus shutdown,
> > > from a "will reboot/kexec" scsi bus shutdown is something I have absolutely
> > > NO CLUE on how to go about doing properly.
> > 
> > Neither do I.

It is so easy, it made me cry in happiness:
	#include <linux/kernel.h>

	if (system_state == SYSTEM_RESTART) {
		/* it is a reboot */
	}

> > My understandin is that Suspend2 suspends all devices, scsi bus
> > included, in order to get a consistent snapshot; it then resumes the
> > necessary devices in order to write the snapshot to disk. Currently
> > this causes a disk spin-down and spin-up, which is bad for the disk
> > and bad for suspend time.
> 
> Suspend2 makes the same driver calls (or should if it doesn't). I'd
> expect that any issue like this with Suspend2 would also apply to
> swsusp. If that's not true, please let me know and I'll fix that.

No drivers seem to check system_state for SYSTEM_SUSPEND_DISK.  Looks like
something that needs a fix.

The fix I need for scsi_bus_shutdown is MUCH easier, since SYSTEM_RESTART is
always a reason to NOT spin down.  For SYSTEM_SUSPEND_DISK, I don't know (I
didn't study the kernel/power/disk.c code).

> > > Suspend2 2.2.8 + kernel 2.6.18 is corrupting the page cache here, do *not*
> > > use it if you value your data.
> > 
> > Does it?! During suspend, you mean? I was just about to test that...
> 
> Works fine for me, but I have had some reports of that. I've only tested
> amd64 so far, and am just about to see if I can reproduce it on x86. I

I had also silent corruption that ended up with ext3 doing very bad things
and hanging (no in-disk filesystem corruption though) even with
suspend-to-RAM (S3) in 2.6.17+suspend2.  So it may be older than 2.2.7,
and/or the mainline change that broke it might have been from 2.6.16 to
2.6.17.

At least now the kernel is screaming blood murder, so it is not silent
anymore.

-- 
  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh