[PATCH v10 06/24] coresight: add try_get_module() in coresight_grab_device()

[Tingwei Zhang]

When coresight device is in an active session, driver module of
that device should not be removed. Use try_get_module() in
coresight_grab_device() to prevent module to be unloaded.
Use get_device()/put_device() to protect device data
in the middle of active session.

Signed-off-by: Tingwei Zhang <ting...@codeaurora.org>
Tested-by: Mike Leach <mike.le...@linaro.org>
Suggested-by: Suzuki K Poulose <suzuki.poul...@arm.com>
---
 drivers/hwtracing/coresight/coresight.c | 60 ++++++++++++++++++++++---
 1 file changed, 53 insertions(+), 7 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight.c 
b/drivers/hwtracing/coresight/coresight.c
index cd17aea6b50d..b040d4421f84 100644
--- a/drivers/hwtracing/coresight/coresight.c
+++ b/drivers/hwtracing/coresight/coresight.c
@@ -633,13 +633,45 @@ struct coresight_device *coresight_get_sink_by_id(u32 id)
        return dev ? to_coresight_device(dev) : NULL;
 }
 
+/**
+ * coresight_get_ref- Helper function to increase reference count to module
+ * and device.
+ * Return true in successful case and power up the device.
+ * Return false when failed to get reference of module.
+ */
+static inline bool coresight_get_ref(struct coresight_device *csdev)
+{
+       struct device *dev = csdev->dev.parent;
+
+       /* Make sure the driver can't be removed */
+       if (!try_module_get(dev->driver->owner))
+               return false;
+       /* Make sure the device can't go away */
+       get_device(dev);
+       pm_runtime_get_sync(dev);
+       return true;
+}
+
+/**
+ * coresight_put_ref- Helper function to decrease reference count to module
+ * and device. Power off the device.
+ */
+static inline void coresight_put_ref(struct coresight_device *csdev)
+{
+       struct device *dev = csdev->dev.parent;
+
+       pm_runtime_put(dev);
+       put_device(dev);
+       module_put(dev->driver->owner);
+}
+
 /*
  * coresight_grab_device - Power up this device and any of the helper
  * devices connected to it for trace operation. Since the helper devices
  * don't appear on the trace path, they should be handled along with the
  * the master device.
  */
-static void coresight_grab_device(struct coresight_device *csdev)
+static int coresight_grab_device(struct coresight_device *csdev)
 {
        int i;
 
@@ -648,9 +680,20 @@ static void coresight_grab_device(struct coresight_device 
*csdev)
 
                child  = csdev->pdata->conns[i].child_dev;
                if (child && child->type == CORESIGHT_DEV_TYPE_HELPER)
-                       pm_runtime_get_sync(child->dev.parent);
+                       if (!coresight_get_ref(child))
+                               goto err;
+       }
+       if (coresight_get_ref(csdev))
+               return 0;
+err:
+       for (i--; i >= 0; i--) {
+               struct coresight_device *child;
+
+               child  = csdev->pdata->conns[i].child_dev;
+               if (child && child->type == CORESIGHT_DEV_TYPE_HELPER)
+                       coresight_put_ref(child);
        }
-       pm_runtime_get_sync(csdev->dev.parent);
+       return -ENODEV;
 }
 
 /*
@@ -661,13 +704,13 @@ static void coresight_drop_device(struct coresight_device 
*csdev)
 {
        int i;
 
-       pm_runtime_put(csdev->dev.parent);
+       coresight_put_ref(csdev);
        for (i = 0; i < csdev->pdata->nr_outport; i++) {
                struct coresight_device *child;
 
                child  = csdev->pdata->conns[i].child_dev;
                if (child && child->type == CORESIGHT_DEV_TYPE_HELPER)
-                       pm_runtime_put(child->dev.parent);
+                       coresight_put_ref(child);
        }
 }
 
@@ -686,7 +729,7 @@ static int _coresight_build_path(struct coresight_device 
*csdev,
                                 struct coresight_device *sink,
                                 struct list_head *path)
 {
-       int i;
+       int i, ret;
        bool found = false;
        struct coresight_node *node;
 
@@ -716,11 +759,14 @@ static int _coresight_build_path(struct coresight_device 
*csdev,
         * is tell the PM runtime core we need this element and add a node
         * for it.
         */
+       ret = coresight_grab_device(csdev);
+       if (ret)
+               return ret;
+
        node = kzalloc(sizeof(struct coresight_node), GFP_KERNEL);
        if (!node)
                return -ENOMEM;
 
-       coresight_grab_device(csdev);
        node->csdev = csdev;
        list_add(&node->link, path);
 
-- 
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