swsusp doesn't suspend devices

swsusp doesn't suspend devices

[Pierre Ossman]

It would seem that swsusp doesn't properly suspend devices, or more
precisely it wakes them up again before suspending the machine.

The problem is in swsusp_suspend(). It is designed as if
swsusp_arch_suspend() would suspend the hardware, when in fact all it
does is prepare for a suspend. The effect is that devices are brought
back up because swsusp_suspend() believes it is resuming.

Below is a patch that uses the same system as kernel/power/disk.c to
determine if it's suspending or resuming. The patch brings up a new
problem though, disk writes generate a huge amount of "scheduling while
atomic".

---

Index: linux-wbsd/kernel/power/swsusp.c
===================================================================
--- linux-wbsd/kernel/power/swsusp.c    (revision 165)
+++ linux-wbsd/kernel/power/swsusp.c    (working copy)
@@ -84,6 +84,8 @@
 /* Local variables that should not be affected by save */
 static unsigned int nr_copy_pages __nosavedata = 0;

+static int in_suspend __nosavedata = 0;
+
 /* Suspend pagedir is allocated before final copy, therefore it
    must be freed after resume

@@ -897,15 +899,18 @@
                return error;
        }

+       in_suspend = 1;
        save_processor_state();
        if ((error = swsusp_arch_suspend()))
                printk("Error %d suspending\n", error);
-       /* Restore control flow magically appears here */
-       restore_processor_state();
-       BUG_ON (nr_copy_pages_check != nr_copy_pages);
-       restore_highmem();
-       device_power_up();
-       local_irq_enable();
+       if (!in_suspend || error) {
+               /* Restore control flow magically appears here */
+               restore_processor_state();
+               BUG_ON (nr_copy_pages_check != nr_copy_pages);
+               restore_highmem();
+               device_power_up();
+               local_irq_enable();
+       }
        return error;
 }

Re: swsusp doesn't suspend devices

[Rafael J. Wysocki]

On Wednesday, 7 of September 2005 13:20, Pierre Ossman wrote:
> It would seem that swsusp doesn't properly suspend devices, or more
> precisely it wakes them up again before suspending the machine.

Yes, it does.  By design.

Greetings,
Rafael


-- 
- Would you tell me, please, which way I ought to go from here?
- That depends a good deal on where you want to get to.
		-- Lewis Carroll "Alice's Adventures in Wonderland"

Re: swsusp doesn't suspend devices

[Pierre Ossman]

Rafael J. Wysocki wrote:

>On Wednesday, 7 of September 2005 13:20, Pierre Ossman wrote:
>  
>
>>It would seem that swsusp doesn't properly suspend devices, or more
>>precisely it wakes them up again before suspending the machine.
>>    
>>
>
>Yes, it does.  By design.
>
>  
>

That seems counter-productive, so I'm obviously missing something.

Re: swsusp doesn't suspend devices

[Rafael J. Wysocki]

On Wednesday, 7 of September 2005 22:17, Pierre Ossman wrote:
> Rafael J. Wysocki wrote:
> 
> >On Wednesday, 7 of September 2005 13:20, Pierre Ossman wrote:
> >  
> >
> >>It would seem that swsusp doesn't properly suspend devices, or more
> >>precisely it wakes them up again before suspending the machine.
> >>    
> >>
> >
> >Yes, it does.  By design.
> >
> >  
> >
> 
> That seems counter-productive, so I'm obviously missing something.

In swsusp, the suspend consists of freezing processes, suspending devices, turning off
interrupts, and creating a memory snapshot (the image) in that state (ie of the "frozen"
system).  Afterwards the image is in memory and it has to be written to a swap partition.
For this purpose we need to resume some devices, in particular the disk that contains
this swap partition, but it always relies on some other devices that have to be resumed
as well.  In principle we could check what devices have to be resumed, but currently
we just resume them all.  An additional upside of this approach is that the suspend
and resume code is (almost) identical.

Greetings,
Rafael


-- 
- Would you tell me, please, which way I ought to go from here?
- That depends a good deal on where you want to get to.
		-- Lewis Carroll "Alice's Adventures in Wonderland"

Re: swsusp doesn't suspend devices

[Pavel Machek]

Hi!

> It would seem that swsusp doesn't properly suspend devices, or more
> precisely it wakes them up again before suspending the machine.

Yes, and that's okay.

 What happens to devices during swsusp? They seem to be resumed
during system suspend?

A: That's correct. We need to resume them if we want to write image to
disk. Whole sequence goes like

      Suspend part
      ~~~~~~~~~~~~
      running system, user asks for suspend-to-disk

      user processes are stopped

      suspend(PMSG_FREEZE): devices are frozen so that they don't
interfere
                      with state snapshot

      state snapshot: copy of whole used memory is taken with
interrupts disabled

      resume(): devices are woken up so that we can write image to
swap

      write image to swap

      suspend(PMSG_SUSPEND): suspend devices so that we can power off

      turn the power off

      Resume part
      ~~~~~~~~~~~
      (is actually pretty similar)

      running system, user asks for suspend-to-disk

      user processes are stopped (in common case there are none, but
with resume-from-initrd, noone k\nows)

      read image from disk

      suspend(PMSG_FREEZE): devices are frozen so that they don't
interfere
                      with image restoration

      image restoration: rewrite memory with image

      resume(): devices are woken up so that system can continue

      thaw all user processes

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