[RFC PATCH v2 02/11] PCI/P2PDMA: Avoid pci_get_slot() which sleeps

[Logan Gunthorpe]

In order to use upstream_bridge_distance_warn() from a dma_map function,
it must not sleep. However, pci_get_slot() takes the pci_bus_sem so it
might sleep.

In order to avoid this, try to get the host bridge's device from
bus->self, and if that is not set just get the first element in the
list. It should be impossible for the host bridges device to go away
while references are held on child devices, so the first element
should not change and this should be safe.

Signed-off-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
---
 drivers/pci/p2pdma.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
index bd89437faf06..2135fe69bb07 100644
--- a/drivers/pci/p2pdma.c
+++ b/drivers/pci/p2pdma.c
@@ -311,11 +311,15 @@ static const struct pci_p2pdma_whitelist_entry {
 static bool __host_bridge_whitelist(struct pci_host_bridge *host,
 				    bool same_host_bridge)
 {
-	struct pci_dev *root = pci_get_slot(host->bus, PCI_DEVFN(0, 0));
 	const struct pci_p2pdma_whitelist_entry *entry;
+	struct pci_dev *root = host->bus->self;
 	unsigned short vendor, device;
 
 	if (!root)
+		root = list_first_entry_or_null(&host->bus->devices,
+						struct pci_dev, bus_list);
+
+	if (!root || root->devfn)
 		return false;
 
 	vendor = root->vendor;
-- 
2.20.1