RE: [PATCH 3/3] PCI: hv: Add pci_destroy_slot() in pci_devices_present_work(), if necessary

[Michael Kelley]

From: Dexuan Cui <decui@xxxxxxxxxxxxx>  Sent: Wednesday, March 20, 2019 5:36 PM
> 
> > From: Michael Kelley <mikelley@xxxxxxxxxxxxx>
> > > ...
> > > diff --git a/drivers/pci/controller/pci-hyperv.c
> > > @@ -1776,6 +1776,10 @@ static void pci_devices_present_work(struct
> > work_struct *work)
> > >  		hpdev = list_first_entry(&removed, struct hv_pci_dev,
> > >  					 list_entry);
> > >  		list_del(&hpdev->list_entry);
> > > +
> > > +		if (hpdev->pci_slot)
> > > +			pci_destroy_slot(hpdev->pci_slot);
> >
> > The code is inconsistent in whether hpdev->pci_slot is set to NULL after calling
> > pci_destory_slot().
> Here, in pci_devices_present_work(), it's unnecessary to set it to NULL,
> Because:
> 1) the "hpdev" is removed from hbus->children and it can not be seen
> elsewhere;
> 2) the "hpdev" struct is freed in the below put_pcichild():
> 
>      while (!list_empty(&removed)) {
>                 hpdev = list_first_entry(&removed, struct hv_pci_dev,
>                                          list_entry);
>                 list_del(&hpdev->list_entry);
> 
>                 if (hpdev->pci_slot)
>                         pci_destroy_slot(hpdev->pci_slot);
> 
>                 put_pcichild(hpdev);
>         }
> 
> > Patch 2 in this series does set it to NULL, but this code does not.
> In Patch2, i.e. in the code path hv_pci_remove() -> hv_pci_remove_slots(),
> we must set hpdev->pci_slot to NULL, otherwise, later, due to
> hv_pci_remove() -> hv_pci_bus_exit() ->
> hv_pci_devices_present() with the zero "relations", we'll double-free the
> "hpdev" struct in pci_devices_present_work() -- see the above.
> 
> > And the code in hv_eject_device_work() does not set it to NULL.
> It's unnecessary to set hpdev->pci_slot to NULL in hv_eject_device_work(),
> Because in hv_eject_device_work():
> 1) the "hpdev" is removed from hbus->children and it can not be seen
> elsewhere;
> 2) the "hpdev" struct is freed at the end of hv_eject_device_work() with my
> first patch: [PATCH 1/3] PCI: hv: Fix a memory leak in hv_eject_device_work().
> 
> > It looks like all the places that test the value of hpdev->pci_slot or call
> > pci_destroy_slot() are serialized, so it looks like it really doesn't matter.  But
> > when
> > the code is inconsistent about setting to NULL, it always makes me wonder if
> > there
> > is a reason.
> >
> > Michael
> 

Reviewed-by:  Michael Kelley <mikelley@xxxxxxxxxxxxx>