[PATCH v2 6/7] s390/pci: Set MSI_FLAG_NO_AFFINITY at IRQ init time

[Tobias Schumacher]

MSI_FLAG_NO_AFFINITY is added to zpci_msi_parent_ops.required_flags from
zpci_create_parent_msi_domain(), which runs for every new PCI bus,
including buses created at runtime from a hotplug availability event.

That is a non-atomic read-modify-write on a field which
msi_lib_init_dev_msi_info() reads without a common lock while setting up
MSI for a device on an already existing bus:

      required_flags = pops->required_flags;

The stored value is always the same, so no caller observes a change, but
the race need not exist: irq_delivery is decided once in zpci_irq_init()
and never changes afterwards.

Set the flag there instead, before any parent domain exists.

Signed-off-by: Tobias Schumacher <ts@xxxxxxxxxxxxx>
---
 arch/s390/pci/pci_irq.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/s390/pci/pci_irq.c b/arch/s390/pci/pci_irq.c
index 682bceb6525e..661867a1ffad 100644
--- a/arch/s390/pci/pci_irq.c
+++ b/arch/s390/pci/pci_irq.c
@@ -523,9 +523,6 @@ int zpci_create_parent_msi_domain(struct zpci_bus *zbus)
 		return -ENOMEM;
 	}
 
-	if (irq_delivery == FLOATING)
-		zpci_msi_parent_ops.required_flags |= MSI_FLAG_NO_AFFINITY;
-
 	zbus->msi_parent_domain = msi_create_parent_irq_domain(&info, &zpci_msi_parent_ops);
 	if (!zbus->msi_parent_domain) {
 		irq_domain_free_fwnode(info.fwnode);
@@ -636,6 +633,9 @@ int __init zpci_irq_init(void)
 	if (s390_pci_force_floating)
 		irq_delivery = FLOATING;
 
+	if (irq_delivery == FLOATING)
+		zpci_msi_parent_ops.required_flags |= MSI_FLAG_NO_AFFINITY;
+
 	if (irq_delivery == DIRECTED)
 		zpci_airq.handler = zpci_directed_irq_handler;
 

-- 
2.53.0