[PATCH] coresight: syscfg: Fix null pointer dereference when configfs init fails

If cscfg_configfs_init() fails, cscfg_init() takes the exit_err path:

	cscfg_init() -> cscfg_clear_device() -> cscfg_configfs_release()
		     -> configfs_unregister_subsystem()

which tears down a configfs subsystem that was never registered.
configfs_unregister_subsystem() begins with:

	struct dentry *dentry = dget(group->cg_item.ci_dentry);
	struct dentry *root = dentry->d_sb->s_root;

ci_dentry is assigned in configfs_create_dir() only once the subsystem
directory has been created, which never happened here.  cscfg_mgr
comes from kzalloc_obj(), so ci_dentry is still NULL, and dget()
hands a NULL dentry back unchanged - the next line dereferences it.

Handle the failure in cscfg_init() directly: unregister the device and
return the error, releasing the devres-allocated config item type and
cscfg_mgr without touching the subsystem.

Fixes: a13d5a246aca ("coresight: syscfg: Add initial configfs support")
Suggested-by: Leo Yan <leo.yan@arm.com>
Link: https://lore.kernel.org/all/20260924162404.GN200420@e132581.arm.com/ (local)
Signed-off-by: Yingchao Deng <redacted>
---
 drivers/hwtracing/coresight/coresight-syscfg.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-syscfg.c b/drivers/hwtracing/coresight/coresight-syscfg.c
index 2bfdd7b45e49..00b29d1656c0 100644
--- a/drivers/hwtracing/coresight/coresight-syscfg.c
+++ b/drivers/hwtracing/coresight/coresight-syscfg.c

@@ -1299,8 +1299,10 @@ int __init cscfg_init(void)
 
 	/* initialise configfs subsystem */
 	err = cscfg_configfs_init(cscfg_mgr);
-	if (err)
-		goto exit_err;
+	if (err) {
+		device_unregister(cscfg_device());
+		return err;
+	}
 
 	/* preload built-in configurations */
 	err = cscfg_preload(THIS_MODULE);

-- 
2.33.0