[PATCH 01/33] PCI: Prepare to protect against concurrent isolated cpuset change

[Frederic Weisbecker <frederic@kernel.org>]

HK_TYPE_DOMAIN will soon integrate cpuset isolated partitions and
therefore be made modifyable at runtime. Synchronize against the cpumask
update using RCU.

The RCU locked section includes both the housekeeping CPU target
election for the PCI probe work and the work enqueue.

This way the housekeeping update side will simply need to flush the
pending related works after updating the housekeeping mask in order to
make sure that no PCI work ever executes on an isolated CPU. This part
will be handled in a subsequent patch.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
 drivers/pci/pci-driver.c | 47 ++++++++++++++++++++++++++++++++--------
 1 file changed, 38 insertions(+), 9 deletions(-)

diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
index 302d61783f6c..7b74d22b20f7 100644
--- a/drivers/pci/pci-driver.c
+++ b/drivers/pci/pci-driver.c
@@ -302,9 +302,8 @@ struct drv_dev_and_id {
 	const struct pci_device_id *id;
 };
 
-static long local_pci_probe(void *_ddi)
+static int local_pci_probe(struct drv_dev_and_id *ddi)
 {
-	struct drv_dev_and_id *ddi = _ddi;
 	struct pci_dev *pci_dev = ddi->dev;
 	struct pci_driver *pci_drv = ddi->drv;
 	struct device *dev = &pci_dev->dev;
@@ -338,6 +337,19 @@ static long local_pci_probe(void *_ddi)
 	return 0;
 }
 
+struct pci_probe_arg {
+	struct drv_dev_and_id *ddi;
+	struct work_struct work;
+	int ret;
+};
+
+static void local_pci_probe_callback(struct work_struct *work)
+{
+	struct pci_probe_arg *arg = container_of(work, struct pci_probe_arg, work);
+
+	arg->ret = local_pci_probe(arg->ddi);
+}
+
 static bool pci_physfn_is_probed(struct pci_dev *dev)
 {
 #ifdef CONFIG_PCI_IOV
@@ -362,34 +374,51 @@ static int pci_call_probe(struct pci_driver *drv, struct pci_dev *dev,
 	dev->is_probed = 1;
 
 	cpu_hotplug_disable();
-
 	/*
 	 * Prevent nesting work_on_cpu() for the case where a Virtual Function
 	 * device is probed from work_on_cpu() of the Physical device.
 	 */
 	if (node < 0 || node >= MAX_NUMNODES || !node_online(node) ||
 	    pci_physfn_is_probed(dev)) {
-		cpu = nr_cpu_ids;
+		error = local_pci_probe(&ddi);
 	} else {
 		cpumask_var_t wq_domain_mask;
+		struct pci_probe_arg arg = { .ddi = &ddi };
+
+		INIT_WORK_ONSTACK(&arg.work, local_pci_probe_callback);
 
 		if (!zalloc_cpumask_var(&wq_domain_mask, GFP_KERNEL)) {
 			error = -ENOMEM;
 			goto out;
 		}
+
+		/*
+		 * The target election and the enqueue of the work must be within
+		 * the same RCU read side section so that when the workqueue pool
+		 * is flushed after a housekeeping cpumask update, further readers
+		 * are guaranteed to queue the probing work to the appropriate
+		 * targets.
+		 */
+		rcu_read_lock();
 		cpumask_and(wq_domain_mask,
 			    housekeeping_cpumask(HK_TYPE_WQ),
 			    housekeeping_cpumask(HK_TYPE_DOMAIN));
 
 		cpu = cpumask_any_and(cpumask_of_node(node),
 				      wq_domain_mask);
+		if (cpu < nr_cpu_ids) {
+			schedule_work_on(cpu, &arg.work);
+			rcu_read_unlock();
+			flush_work(&arg.work);
+			error = arg.ret;
+		} else {
+			rcu_read_unlock();
+			error = local_pci_probe(&ddi);
+		}
+
 		free_cpumask_var(wq_domain_mask);
+		destroy_work_on_stack(&arg.work);
 	}
-
-	if (cpu < nr_cpu_ids)
-		error = work_on_cpu(cpu, local_pci_probe, &ddi);
-	else
-		error = local_pci_probe(&ddi);
 out:
 	dev->is_probed = 0;
 	cpu_hotplug_enable();
-- 
2.51.0