PCI: Avoid unnecessary CPU switch when calling driver .probe() method
If we are already on a CPU local to the device, call the driver .probe()
method directly without using work_on_cpu().
This is a workaround for a lockdep warning in the following scenario:
pci_call_probe
work_on_cpu(cpu, local_pci_probe, ...)
driver .probe
pci_enable_sriov
...
pci_bus_add_device
...
pci_call_probe
work_on_cpu(cpu, local_pci_probe, ...)
It would be better to fix PCI so we don't call VF driver .probe() methods
from inside a PF driver .probe() method, but that's a bigger project.
[bhelgaas: open bugzilla, rework comments & changelog]
Link: https://bugzilla.kernel.org/show_bug.cgi?id=65071
Link: http://lkml.kernel.org/r/CAE9FiQXYQEAZ=0sG6+2OdffBqfLS9MpoN1xviRR9aDbxPxcKxQ@mail.gmail.com
Link: http://lkml.kernel.org/r/20130624195942.40795.27292.stgit@ahduyck-cp1.jf.intel.com
Tested-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Tejun Heo <tj@kernel.org>
Acked-by: Yinghai Lu <yinghai@kernel.org>diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
index 9042fdb..7edd5c3 100644
--- a/drivers/pci/pci-driver.c
+++ b/drivers/pci/pci-driver.c
@@ -288,12 +288,27 @@
int error, node;
struct drv_dev_and_id ddi = { drv, dev, id };
- /* Execute driver initialization on node where the device's
- bus is attached to. This way the driver likely allocates
- its local memory on the right node without any need to
- change it. */
+ /*
+ * Execute driver initialization on node where the device is
+ * attached. This way the driver likely allocates its local memory
+ * on the right node.
+ */
node = dev_to_node(&dev->dev);
- if (node >= 0) {
+
+ /*
+ * On NUMA systems, we are likely to call a PF probe function using
+ * work_on_cpu(). If that probe calls pci_enable_sriov() (which
+ * adds the VF devices via pci_bus_add_device()), we may re-enter
+ * this function to call the VF probe function. Calling
+ * work_on_cpu() again will cause a lockdep warning. Since VFs are
+ * always on the same node as the PF, we can work around this by
+ * avoiding work_on_cpu() when we're already on the correct node.
+ *
+ * Preemption is enabled, so it's theoretically unsafe to use
+ * numa_node_id(), but even if we run the probe function on the
+ * wrong node, it should be functionally correct.
+ */
+ if (node >= 0 && node != numa_node_id()) {
int cpu;
get_online_cpus();
@@ -305,6 +320,7 @@
put_online_cpus();
} else
error = local_pci_probe(&ddi);
+
return error;
}