+ /*
+ * In all other cases the spa_namespace_lock is taken before the
+ * bdev->bd_mutex lock. But in this case the Linux __blkdev_get()
+ * function calls fops->open() with the bdev->bd_mutex lock held.
+ *
+ * To avoid a potential lock inversion deadlock we preemptively
+ * try to take the spa_namespace_lock(). Normally it will not
+ * be contended and this is safe because spa_open_common() handles
+ * the case where the caller already holds the spa_namespace_lock.
+ *
+ * When it is contended we risk a lock inversion if we were to
+ * block waiting for the lock. Luckily, the __blkdev_get()
+ * function allows us to return -ERESTARTSYS which will result in
+ * bdev->bd_mutex being dropped, reacquired, and fops->open() being
+ * called again. This process can be repeated safely until both
+ * locks are acquired.
+ */
+ if (!mutex_owned(&spa_namespace_lock)) {
+ locked = mutex_tryenter(&spa_namespace_lock);
+ if (!locked)
+ return (-ERESTARTSYS);
+ }
+