Re: [PATCH v2 1/1] coresight: syscfg: fix deadlock on device registration failure

cscfg_create_device() calls put_device() on the error path while holding
cscfg_mutex.  If device_register() fails, put_device() drops the last
reference and invokes cscfg_dev_release(), which takes cscfg_mutex again,
deadlocking.

Module init and exit are serialized by the kernel, so cscfg_mutex is not
needed to protect the allocation and freeing of cscfg_mgr.  Remove the
mutex from cscfg_dev_release() and take it only while cscfg_mgr fields
are being accessed.

Fixes: 199380decc5f ("coresight: configfs: Fix unload of configurations on module exit")
Suggested-by: Leo Yan <leo.yan@arm.com>
Signed-off-by: Yingchao Deng <redacted>
---
  drivers/hwtracing/coresight/coresight-syscfg.c | 18 ++++++------------
  1 file changed, 6 insertions(+), 12 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-syscfg.c b/drivers/hwtracing/coresight/coresight-syscfg.c
index 2bfdd7b45e49..2dd0b29f44e4 100644
--- a/drivers/hwtracing/coresight/coresight-syscfg.c
+++ b/drivers/hwtracing/coresight/coresight-syscfg.c

@@ -1173,27 +1173,21 @@ struct device *cscfg_device(void)
  /* Must have a release function or the kernel will complain on module unload */
  static void cscfg_dev_release(struct device *dev)
  {
-	mutex_lock(&cscfg_mutex);
  	kfree(cscfg_mgr);
  	cscfg_mgr = NULL;
-	mutex_unlock(&cscfg_mutex);
  }
  
  /* a device is needed to "own" some kernel elements such as sysfs entries.  */
  static int cscfg_create_device(void)
  {
  	struct device *dev;
-	int err = -ENOMEM;
-
-	mutex_lock(&cscfg_mutex);
-	if (cscfg_mgr) {
-		err = -EINVAL;
-		goto create_dev_exit_unlock;
-	}
+	int err;
  
  	cscfg_mgr = kzalloc_obj(struct cscfg_manager);
  	if (!cscfg_mgr)
-		goto create_dev_exit_unlock;
+		return -ENOMEM;
+
+	mutex_lock(&cscfg_mutex);
  
  	/* initialise the cscfg_mgr structure */
  	INIT_LIST_HEAD(&cscfg_mgr->csdev_desc_list);

@@ -1204,6 +1198,8 @@ static int cscfg_create_device(void)
  	cscfg_mgr->load_state = CSCFG_NONE;
  	raw_spin_lock_init(&cscfg_mgr->sysfs_store_lock);
  
+	mutex_unlock(&cscfg_mutex);
+
  	/* setup the device */
  	dev = cscfg_device();
  	dev->release = cscfg_dev_release;

@@ -1213,8 +1209,6 @@ static int cscfg_create_device(void)
  	if (err)
  		put_device(dev);
  
-create_dev_exit_unlock:
-	mutex_unlock(&cscfg_mutex);
  	return err;
  }