Re: device_pm_add (was: Re: 2.6.25-git2: BUG: unable to handle kernel paging request at ffffffffffffffff)

[Rafael J. Wysocki]

On Tuesday, 22 of April 2008, Rafael J. Wysocki wrote:
> On Tuesday, 22 of April 2008, Linus Torvalds wrote:
> > 
> > On Tue, 22 Apr 2008, Zdenek Kabelac wrote:
> > > 
> > > Unsure how it is related to my orginal Oops post - but now when I've
> > > debug pagealloc enabled this appeared in my log after resume - should
> > > I open new bug for this - or could this be part of the problem I've
> > > experienced later?
> > > 
> > > (Note - now I'm running commit: 8a81f2738f10ca817c975cec893aa58497e873b2
> > > 
> > >  sd 0:0:0:0: [sda] Starting disk
> > >  mmc0: new SD card at address 5a61
> > >  mmc mmc0:5a61: parent mmc0 is sleeping, will not add
> > >  ------------[ cut here ]------------
> > >  WARNING: at drivers/base/power/main.c:78 device_pm_add+0x6c/0xf0()
> > 
> > This is unrelated to the other issue, I think.
> > 
> > Your warning comes from commit 58aca23226a19983571bd3b65167521fc64f5869, 
> > which admittedly looks like total crap.
> 
> Well, I'm sorry that you think so.
> 
> > Rafael, what's the point of that commit?
> 
> More or less as stated in the changelog.  If we register a child of a sleeping
> device, the child ends up on dpm_active before the parent, so the ordering will
> be wrong during the next suspend.
> 
> That was discussed on linux-pm, mainly with Alan Stern.
> 
> > I read the commit message, but I can't make myself agree with the commit 
> > code itself. If it's a "checking that the order is correct" thing, it 
> > should be a warning, but not change the actual _action_ of the code.
> 
> That is easy to change.  Please find appended a patch for that.
> 
> > Because the commit refused to add the device, it is also then the direct 
> > reason for the oops you get later, as far as I can tell:
> > 
> > >  BUG: unable to handle kernel NULL pointer dereference at 0000000000000050
> > >  IP: [klist_del+29/128] klist_del+0x1d/0x80
> > >  PGD 0
> > >  Oops: 0000 [1] PREEMPT SMP DEBUG_PAGEALLOC
> > >  CPU 0
> > >  Call Trace:
> > >   [bus_remove_device+158/208] bus_remove_device+0x9e/0xd0
> > >   [device_add+1358/1376] device_add+0x54e/0x560
> 
> There is a bug in device_add() that IMO can be fixed this way:
> 
> Index: linux-2.6/drivers/base/core.c
> ===================================================================
> --- linux-2.6.orig/drivers/base/core.c
> +++ linux-2.6/drivers/base/core.c
> @@ -820,11 +820,11 @@ int device_add(struct device *dev)
>  	error = bus_add_device(dev);
>  	if (error)
>  		goto BusError;
> +	bus_attach_device(dev);
>  	error = device_pm_add(dev);
>  	if (error)
>  		goto PMError;
>  	kobject_uevent(&dev->kobj, KOBJ_ADD);
> -	bus_attach_device(dev);
>  	if (parent)
>  		klist_add_tail(&dev->knode_parent, &parent->klist_children);
>  
> The problem is that bus_remove_device() assumes bus_attach_device() to have
> run, AFAICS.

Hm, actually it's better to do this instead IMHO:

---
Prevent bus_remove_device() from crashing if dev->knode_bus has not been
initialized before it's called.

Signed-off-by: Rafael J. Wysocki <rjw@xxxxxxx>
---
 drivers/base/bus.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Index: linux-2.6/drivers/base/bus.c
===================================================================
--- linux-2.6.orig/drivers/base/bus.c
+++ linux-2.6/drivers/base/bus.c
@@ -530,7 +530,8 @@ void bus_remove_device(struct device *de
 		sysfs_remove_link(&dev->bus->p->devices_kset->kobj,
 				  dev->bus_id);
 		device_remove_attrs(dev->bus, dev);
-		klist_del(&dev->knode_bus);
+		if (klist_node_attached(&dev->knode_bus))
+			klist_del(&dev->knode_bus);
 
 		pr_debug("bus: '%s': remove device %s\n",
 			 dev->bus->name, dev->bus_id);
--
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