[PATCH] PCI/proc: Fix race between pci_proc_init() and pci_bus_add_device()

["Krzysztof Wilczyński" <kwilczynski@kernel.org>]

pci_proc_attach_device() creates procfs entries for PCI devices and is
called from pci_bus_add_device().  It returns early if proc_initialized
is not yet set.

On x86 with ACPI, PCI enumeration occurs at subsys_initcall, before
pci_proc_init() sets proc_initialized at device_initcall.  The
for_each_pci_dev() loop in pci_proc_init() creates procfs entries for
these already-enumerated devices.  This loop runs without holding any
lock.

On ARM64 with devicetree, PCI host bridges probe at device_initcall.
With async probing enabled, pci_bus_add_device() can run concurrently
with pci_proc_init(), and both may call pci_proc_attach_device() for
the same device, leading to duplicate proc_create_data() calls.

Thus, wrap the for_each_pci_dev() loop with pci_lock_rescan_remove() to
serialise against concurrent PCI bus operations.  Add an early return in
pci_proc_attach_device() when dev->procent is already set, making the
function idempotent and symmetric with pci_proc_detach_device() which
clears this field.

While at it, update code to match preferred style and help with
readability.

Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
---
 drivers/pci/proc.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/proc.c b/drivers/pci/proc.c
index ce36e35681e8..9326f235bc58 100644
--- a/drivers/pci/proc.c
+++ b/drivers/pci/proc.c
@@ -425,6 +425,9 @@ int pci_proc_attach_device(struct pci_dev *dev)
 	if (!proc_initialized)
 		return -EACCES;
 
+	if (dev->procent)
+		return 0;
+
 	if (!bus->procdir) {
 		if (pci_proc_domain(bus)) {
 			sprintf(name, "%04x:%02x", pci_domain_nr(bus),
@@ -464,12 +467,17 @@ int pci_proc_detach_bus(struct pci_bus *bus)
 static int __init pci_proc_init(void)
 {
 	struct pci_dev *dev = NULL;
+
 	proc_bus_pci_dir = proc_mkdir("bus/pci", NULL);
 	proc_create_seq("devices", 0, proc_bus_pci_dir,
-		    &proc_bus_pci_devices_op);
+			&proc_bus_pci_devices_op);
+
 	proc_initialized = 1;
+
+	pci_lock_rescan_remove();
 	for_each_pci_dev(dev)
 		pci_proc_attach_device(dev);
+	pci_unlock_rescan_remove();
 
 	return 0;
 }
-- 
2.54.0