The "goto error" pattern is notorious for introducing subtle resource
leaks. Use the new cleanup.h helpers for PCI device reference counts and
locks.

Similar to the new put_device() and device_lock() cleanup helpers,
__free(put_device) and guard(device), define the same for PCI devices,
__free(pci_dev_put) and guard(pci_dev).  These helpers eliminate the
need for "goto free;" and "goto unlock;" patterns. For example, A
'struct pci_dev *' instance declared as:

    struct pci_dev *pdev __free(pci_dev_put) = NULL;

...will automatically call pci_dev_put() if @pdev is non-NULL when @pdev
goes out of scope (automatic variable scope). If a function wants to
invoke pci_dev_put() on error, but return @pdev on success, it can do:

    return no_free_ptr(pdev);

...or:

    return_ptr(pdev);

For potential cleanup opportunity there are 587 open-coded calls to
pci_dev_put() in the kernel with 65 instances within 10 lines of a goto
statement with the CXL driver threatening to add another one.

The guard() helper holds the associated lock for the remainder of the
current scope in which it was invoked. So, for example:

    func(...)
    {
        if (...) {
            ...
            guard(pci_dev); /* pci_dev_lock() invoked here */
            ...
        } /* <- implied pci_dev_unlock() triggered here */
    }

There are 15 invocations of pci_dev_unlock() in the kernel with 5
instances within 10 lines of a goto statement. Again, the CXL driver is
threatening to add another.

Introduce these helpers to preclude the addition of new more error prone
goto put; / goto unlock; sequences. For now, these helpers are used in
drivers/cxl/pci.c to allow ACPI error reports to be fed back into the
CXL driver associated with the PCI device identified in the report.

Cc: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Link: https://lore.kernel.org/r/20231220-cxl-cper-v5-8-1bb8a4ca2c7a@intel.com


[djbw: rewrite changelog]
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>