[PATCH 4.1 013/159] cxl: Fix unbalanced pci_dev_get in cxl_probe

From: Greg Kroah-Hartman
Date: Sat Sep 26 2015 - 17:51:42 EST

4.1-stable review patch. If anyone has any objections, please let me know.


From: Daniel Axtens <dja@xxxxxxxxxx>

commit 2925c2fdf1e0eb642482f5b30577e9435aaa8edb upstream.

Currently the first thing we do in cxl_probe is to grab a reference
on the pci device. Later on, we call device_register on our adapter.
In our remove path, we call device_unregister, but we never call
pci_dev_put. We therefore leak the device every time we do a

device_register/unregister is sufficient to hold the reference.
Therefore, drop the call to pci_dev_get.

Here's why this is safe.
The proposed cxl_probe(pdev) calls cxl_adapter_init:
a) init calls cxl_adapter_alloc, which creates a struct cxl,
conventionally called adapter. This struct contains a
device entry, adapter->dev.

b) init calls cxl_configure_adapter, where we set
adapter->dev.parent = &dev->dev (here dev is the pci dev)

So at this point, the cxl adapter's device's parent is the PCI
device that I want to be refcounted properly.

c) init calls cxl_register_adapter
*) cxl_register_adapter calls device_register(&adapter->dev)

So now we're in device_register, where dev is the adapter device, and
we want to know if the PCI device is safe after we return.

device_register(&adapter->dev) calls device_initialize() and then

device_add() does a get_device(). device_add() also explicitly grabs
the device's parent, and calls get_device() on it:

parent = get_device(dev->parent);

So therefore, device_register() takes a lock on the parent PCI dev,
which is what pci_dev_get() was guarding. pci_dev_get() can therefore
be safely removed.

Fixes: f204e0b8cedd ("cxl: Driver code for powernv PCIe based cards for userspace access")
Signed-off-by: Daniel Axtens <dja@xxxxxxxxxx>
Acked-by: Ian Munsie <imunsie@xxxxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

drivers/misc/cxl/pci.c | 2 --
1 file changed, 2 deletions(-)

--- a/drivers/misc/cxl/pci.c
+++ b/drivers/misc/cxl/pci.c
@@ -1046,8 +1046,6 @@ static int cxl_probe(struct pci_dev *dev
int slice;
int rc;

- pci_dev_get(dev);
if (cxl_verbose)

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