diff mbox series

[PATCHv3,4/5] pci: walk bus recursively

Message ID 20241022224851.340648-5-kbusch@meta.com (mailing list archive)
State Accepted
Delegated to: Bjorn Helgaas
Headers show
Series pci cleanup/prep patches | expand

Commit Message

Keith Busch Oct. 22, 2024, 10:48 p.m. UTC 
From: Keith Busch <kbusch@kernel.org>

The original implementation purposefully chose a non-recursive walk,
presumably as a precaution on stack use. We do recursive bus walking in
other places though. For example:

  pci_bus_resettable
  pci_stop_bus_device
  pci_remove_bus_device
  pci_bus_allocate_dev_resources

So, recursive pci bus walking is well tested and safe, and the
implementation is easier to follow. The motivation for changing it now
is to make it easier to introduce finer grain locking in the future.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>
---
 drivers/pci/bus.c | 36 +++++++++++-------------------------
 1 file changed, 11 insertions(+), 25 deletions(-)

Comments

Lukas Wunner Nov. 11, 2024, 8:21 a.m. UTC | #1 
On Tue, Oct 22, 2024 at 03:48:50PM -0700, Keith Busch wrote:
> The original implementation purposefully chose a non-recursive walk,
> presumably as a precaution on stack use. We do recursive bus walking in
> other places though. For example:
> 
>   pci_bus_resettable
>   pci_stop_bus_device
>   pci_remove_bus_device
>   pci_bus_allocate_dev_resources
> 
> So, recursive pci bus walking is well tested and safe, and the
> implementation is easier to follow. The motivation for changing it now
> is to make it easier to introduce finer grain locking in the future.

Hm, I find the loss of non-recursive bus walking regrettable.

If the solution proposed earlier today...

https://lore.kernel.org/all/ZzG5koPOn16KQ8uM@wunner.de/

... is workable and we find it doesn't need recursive bus walking,
perhaps we should consider reverting this change (which is now
e24eafdda271 on pci/locking).

Thanks,

Lukas
diff mbox series

Patch

diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
index b863b8bdd6ee6..9c552396241e0 100644
--- a/drivers/pci/bus.c
+++ b/drivers/pci/bus.c
@@ -399,37 +399,23 @@  void pci_bus_add_devices(const struct pci_bus *bus)
 }
 EXPORT_SYMBOL(pci_bus_add_devices);
 
-static void __pci_walk_bus(struct pci_bus *top, int (*cb)(struct pci_dev *, void *),
-			   void *userdata)
+static int __pci_walk_bus(struct pci_bus *top, int (*cb)(struct pci_dev *, void *),
+			  void *userdata)
 {
 	struct pci_dev *dev;
-	struct pci_bus *bus;
-	struct list_head *next;
-	int retval;
+	int ret = 0;
 
-	bus = top;
-	next = top->devices.next;
-	for (;;) {
-		if (next == &bus->devices) {
-			/* end of this bus, go up or finish */
-			if (bus == top)
+	list_for_each_entry(dev, &top->devices, bus_list) {
+		ret = cb(dev, userdata);
+		if (ret)
+			break;
+		if (dev->subordinate) {
+			ret = __pci_walk_bus(dev->subordinate, cb, userdata);
+			if (ret)
 				break;
-			next = bus->self->bus_list.next;
-			bus = bus->self->bus;
-			continue;
 		}
-		dev = list_entry(next, struct pci_dev, bus_list);
-		if (dev->subordinate) {
-			/* this is a pci-pci bridge, do its devices next */
-			next = dev->subordinate->devices.next;
-			bus = dev->subordinate;
-		} else
-			next = dev->bus_list.next;
-
-		retval = cb(dev, userdata);
-		if (retval)
-			break;
 	}
+	return ret;
 }
 
 /**