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authorLinus Torvalds <torvalds@linux-foundation.org>2014-05-02 18:12:54 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2014-05-02 18:12:54 -0700
commite981e79585da98397e34809f4773c7fa5e61317a (patch)
treee97cf5e531b4d67bf9f1747cee0cccf171aceeab
parent54366a7fd68c955795ee4fa87a69faf5938572ea (diff)
parent58b116bce13612e5aa6fcd49ecbd4cf8bb59e835 (diff)
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
-rw-r--r--drivers/base/dd.c17
1 files changed, 17 insertions, 0 deletions
diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 8986b9f22781..62ec61e8f84a 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -52,6 +52,7 @@ static DEFINE_MUTEX(deferred_probe_mutex);
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 @@ static bool driver_deferred_probe_enable = false;
* 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 @@ static void driver_deferred_probe_trigger(void)
* 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 DECLARE_WAIT_QUEUE_HEAD(probe_waitqueue);
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 @@ probe_failed:
/* 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