intel_th: Fix a deadlock in modprobing

Driver initialization tries to request a hub (GTH) driver module from
its probe callback, resulting in a deadlock.

This patch solves the problem by adding a deferred work for requesting
the hub module.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: <stable@vger.kernel.org> # 4.4.x-

2 files changed, 37 insertions, 1 deletions

diff --git a/drivers/hwtracing/intel_th/core.c b/drivers/hwtracing/intel_th/core.c
index 1be543e8e42f..0b112ae689bf 100644
--- a/drivers/hwtracing/intel_th/core.c
+++ b/drivers/hwtracing/intel_th/core.c
@@ -465,6 +465,38 @@ static struct intel_th_subdevice {
         },
 };
 
+#ifdef CONFIG_MODULES
+static void __intel_th_request_hub_module(struct work_struct *work)
+{
+        struct intel_th *th = container_of(work, struct intel_th,
+                                           request_module_work);
+
+        request_module("intel_th_%s", th->hub->name);
+}
+
+static int intel_th_request_hub_module(struct intel_th *th)
+{
+        INIT_WORK(&th->request_module_work, __intel_th_request_hub_module);
+        schedule_work(&th->request_module_work);
+
+        return 0;
+}
+
+static void intel_th_request_hub_module_flush(struct intel_th *th)
+{
+        flush_work(&th->request_module_work);
+}
+#else
+static inline int intel_th_request_hub_module(struct intel_th *th)
+{
+        return -EINVAL;
+}
+
+static inline void intel_th_request_hub_module_flush(struct intel_th *th)
+{
+}
+#endif /* CONFIG_MODULES */
+
 static int intel_th_populate(struct intel_th *th, struct resource *devres,
                              unsigned int ndevres, int irq)
 {
@@ -535,7 +567,7 @@ static int intel_th_populate(struct intel_th *th, struct resource *devres,
                 /* need switch driver to be loaded to enumerate the rest */
                 if (subdev->type == INTEL_TH_SWITCH && !req) {
                         th->hub = thdev;
-                        err = request_module("intel_th_%s", subdev->name);
+                        err = intel_th_request_hub_module(th);
                         if (!err)
                                 req++;
                 }
@@ -652,6 +684,7 @@ void intel_th_free(struct intel_th *th)
 {
         int i;
 
+        intel_th_request_hub_module_flush(th);
         for (i = 0; i < TH_SUBDEVICE_MAX; i++)
                 if (th->thdev[i] != th->hub)
                         intel_th_device_remove(th->thdev[i]);
diff --git a/drivers/hwtracing/intel_th/intel_th.h b/drivers/hwtracing/intel_th/intel_th.h
index 0df22e30673d..04828482600b 100644
--- a/drivers/hwtracing/intel_th/intel_th.h
+++ b/drivers/hwtracing/intel_th/intel_th.h
@@ -205,6 +205,9 @@ struct intel_th {
 
         int                     id;
         int                     major;
+#ifdef CONFIG_MODULES
+        struct work_struct      request_module_work;
+#endif /* CONFIG_MODULES */
 #ifdef CONFIG_INTEL_TH_DEBUG
         struct dentry           *dbg;
 #endif