firewire: enforce access order between generation and node ID, fix "giving up on config rom"

fw_device.node_id and fw_device.generation are accessed without mutexes.
We have to ensure that all readers will get to see node_id updates
before generation updates.

Fixes an inability to recognize devices after "giving up on config rom",
https://bugzilla.redhat.com/show_bug.cgi?id=429950

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>

Reviewed by Nick Piggin <nickpiggin@yahoo.com.au>.

Verified to fix 'giving up on config rom' issues on multiple system and
drive combinations that were previously affected.

Signed-off-by: Jarod Wilson <jwilson@redhat.com>
Signed-off-by: Kristian Høgsberg <krh@redhat.com>

1 files changed, 13 insertions, 2 deletions

diff --git a/drivers/firewire/fw-device.c b/drivers/firewire/fw-device.c
index 56681b3b297b..872df2238609 100644
--- a/drivers/firewire/fw-device.c
+++ b/drivers/firewire/fw-device.c
@@ -27,6 +27,7 @@
 #include <linux/idr.h>
 #include <linux/rwsem.h>
 #include <asm/semaphore.h>
+#include <asm/system.h>
 #include <linux/ctype.h>
 #include "fw-transaction.h"
 #include "fw-topology.h"
@@ -182,9 +183,14 @@ static void fw_device_release(struct device *dev)
 
 int fw_device_enable_phys_dma(struct fw_device *device)
 {
+        int generation = device->generation;
+
+        /* device->node_id, accessed below, must not be older than generation */
+        smp_rmb();
+
         return device->card->driver->enable_phys_dma(device->card,
                                                      device->node_id,
-                                                     device->generation);
+                                                     generation);
 }
 EXPORT_SYMBOL(fw_device_enable_phys_dma);
 
@@ -389,12 +395,16 @@ static int read_rom(struct fw_device *device, int index, u32 * data)
         struct read_quadlet_callback_data callback_data;
         struct fw_transaction t;
         u64 offset;
+        int generation = device->generation;
+
+        /* device->node_id, accessed below, must not be older than generation */
+        smp_rmb();
 
         init_completion(&callback_data.done);
 
         offset = 0xfffff0000400ULL + index * 4;
         fw_send_request(device->card, &t, TCODE_READ_QUADLET_REQUEST,
-                        device->node_id, device->generation, device->max_speed,
+                        device->node_id, generation, device->max_speed,
                         offset, NULL, 4, complete_transaction, &callback_data);
 
         wait_for_completion(&callback_data.done);
@@ -801,6 +811,7 @@ void fw_node_event(struct fw_card *card, struct fw_node *node, int event)
 
                 device = node->data;
                 device->node_id = node->node_id;
+                smp_wmb();  /* update node_id before generation */
                 device->generation = card->generation;
                 if (atomic_read(&device->state) == FW_DEVICE_RUNNING) {
                         PREPARE_DELAYED_WORK(&device->work, fw_device_update);