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From:   Michael Kelley <mikelley@microsoft.com>
To:     Dexuan Cui <decui@microsoft.com>,
        "lorenzo.pieralisi@arm.com" <lorenzo.pieralisi@arm.com>,
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        Sasha Levin <Alexander.Levin@microsoft.com>
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        "jackm@mellanox.com" <jackm@mellanox.com>,
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Subject: RE: [PATCH 3/3] PCI: hv: Add pci_destroy_slot() in
 pci_devices_present_work(), if necessary
Thread-Topic: [PATCH 3/3] PCI: hv: Add pci_destroy_slot() in
 pci_devices_present_work(), if necessary
Thread-Index: AQHU0tIZgD9GMFct2EmlQHf+0/9EJaYVJQAQgAAxdgCACPxPgA==
Date:   Tue, 26 Mar 2019 17:50:00 +0000
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From: Dexuan Cui <decui@microsoft.com>  Sent: Wednesday, March 20, 2019 5:3=
6 PM
>=20
> > From: Michael Kelley <mikelley@microsoft.com>
> > > ...
> > > diff --git a/drivers/pci/controller/pci-hyperv.c
> > > @@ -1776,6 +1776,10 @@ static void pci_devices_present_work(struct
> > work_struct *work)
> > >  		hpdev =3D 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 afte=
r 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():
>=20
>      while (!list_empty(&removed)) {
>                 hpdev =3D list_first_entry(&removed, struct hv_pci_dev,
>                                          list_entry);
>                 list_del(&hpdev->list_entry);
>=20
>                 if (hpdev->pci_slot)
>                         pci_destroy_slot(hpdev->pci_slot);
>=20
>                 put_pcichild(hpdev);
>         }
>=20
> > 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.
>=20
> > 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_wo=
rk().
>=20
> > 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 m=
atter.  But
> > when
> > the code is inconsistent about setting to NULL, it always makes me wond=
er if
> > there
> > is a reason.
> >
> > Michael
>=20

Reviewed-by:  Michael Kelley <mikelley@microsoft.com>