Merge tag 'dt-for-linus' of git://git.secretlab.ca/git/linux
Pull driver core deferred probe fix from Grant Likely:
"Drivercore race condition fix (exposed by devicetree)
This branch fixes a bug where a device can get stuck in the deferred
list even though all its dependencies are met. The bug has existed
for a long time, but new platform conversions to device tree have
exposed it. This patch is needed to get those platforms working.
This was the pending bug fix I mentioned in my previous pull request.
Normally this would go through Greg's tree seeing that it is a
drivercore change, but devicetree exposes the problem. I've discussed
with Greg and he okayed me asking you to pull directly"
* tag 'dt-for-linus' of git://git.secretlab.ca/git/linux:
drivercore: deferral race condition fix
diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 8986b9f..62ec61e 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -52,6 +52,7 @@
static LIST_HEAD(deferred_probe_pending_list);
static LIST_HEAD(deferred_probe_active_list);
static struct workqueue_struct *deferred_wq;
+static atomic_t deferred_trigger_count = ATOMIC_INIT(0);
/**
* deferred_probe_work_func() - Retry probing devices in the active list.
@@ -135,6 +136,17 @@
* This functions moves all devices from the pending list to the active
* list and schedules the deferred probe workqueue to process them. It
* should be called anytime a driver is successfully bound to a device.
+ *
+ * Note, there is a race condition in multi-threaded probe. In the case where
+ * more than one device is probing at the same time, it is possible for one
+ * probe to complete successfully while another is about to defer. If the second
+ * depends on the first, then it will get put on the pending list after the
+ * trigger event has already occured and will be stuck there.
+ *
+ * The atomic 'deferred_trigger_count' is used to determine if a successful
+ * trigger has occurred in the midst of probing a driver. If the trigger count
+ * changes in the midst of a probe, then deferred processing should be triggered
+ * again.
*/
static void driver_deferred_probe_trigger(void)
{
@@ -147,6 +159,7 @@
* into the active list so they can be retried by the workqueue
*/
mutex_lock(&deferred_probe_mutex);
+ atomic_inc(&deferred_trigger_count);
list_splice_tail_init(&deferred_probe_pending_list,
&deferred_probe_active_list);
mutex_unlock(&deferred_probe_mutex);
@@ -265,6 +278,7 @@
static int really_probe(struct device *dev, struct device_driver *drv)
{
int ret = 0;
+ int local_trigger_count = atomic_read(&deferred_trigger_count);
atomic_inc(&probe_count);
pr_debug("bus: '%s': %s: probing driver %s with device %s\n",
@@ -310,6 +324,9 @@
/* Driver requested deferred probing */
dev_info(dev, "Driver %s requests probe deferral\n", drv->name);
driver_deferred_probe_add(dev);
+ /* Did a trigger occur while probing? Need to re-trigger if yes */
+ if (local_trigger_count != atomic_read(&deferred_trigger_count))
+ driver_deferred_probe_trigger();
} else if (ret != -ENODEV && ret != -ENXIO) {
/* driver matched but the probe failed */
printk(KERN_WARNING
