PCI: endpoint: Fix for concurrent memory allocation in OB address region

PCI: endpoint: Fix for concurrent memory allocation in OB address region

commit 04e046ca57ebed3943422dee10eec9e73aec081e upstream.

pci-epc-mem uses a bitmap to manage the Endpoint outbound (OB) address
region. This address region will be shared by multiple endpoint
functions (in the case of multi function endpoint) and it has to be
protected from concurrent access to avoid updating an inconsistent state.

Use a mutex to protect bitmap updates to prevent the memory
allocation API from returning incorrect addresses.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: stable@vger.kernel.org # v4.14+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>