[PATCH v2] cxl: Fix unbalanced pci_dev_get in cxl_probe
dja at axtens.net
Tue Sep 15 15:04:07 AEST 2015
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")
Cc: stable at vger.kernel.org
Signed-off-by: Daniel Axtens <dja at axtens.net>
This is the cxl bug that caused me to catch this a few weeks back:
e642d11bdbfe ("powerpc/eeh: Probe after unbalanced kref check")
I put an printk in the unbalanced kref path and confirmed that it
was printed with the pci_dev_get in and went away with the
drivers/misc/cxl/pci.c | 2 --
1 file changed, 2 deletions(-)
diff --git a/drivers/misc/cxl/pci.c b/drivers/misc/cxl/pci.c
index 02c85160bfe9..a5e977192b61 100644
@@ -1249,8 +1249,6 @@ static int cxl_probe(struct pci_dev *dev, const struct pci_device_id *id)
More information about the Linuxppc-dev