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    cxl: Fix unbalanced pci_dev_get in cxl_probe · 2925c2fd
    Daniel Axtens 提交于
    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
    reflash.
    
    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().
    
    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: f204e0b8 ("cxl: Driver code for powernv PCIe based cards for userspace access")
    Cc: stable@vger.kernel.org
    Signed-off-by: NDaniel Axtens <dja@axtens.net>
    Acked-by: NIan Munsie <imunsie@au1.ibm.com>
    Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>
    2925c2fd
pci.c 42.3 KB