drm/v3d: Fix global performance monitor reference counting

In the SET_GLOBAL ioctl, v3d_perfmon_find() bumps the reference count on
the perfmon it returns, but v3d_perfmon_set_global_ioctl() and
v3d_perfmon_delete() fail to release that reference on several paths:

  1. v3d_perfmon_set_global_ioctl() leaks the reference on its error
     paths.

  2. CLEAR_GLOBAL leaks both the find reference and the reference
     previously stashed in v3d->global_perfmon by the SET_GLOBAL ioctl
     that configured it.

  3. Destroying a perfmon that is the current global perfmon leaks the
     reference stashed by the SET_GLOBAL ioctl.

Release each of these references explicitly.

Cc: stable@vger.kernel.org
Fixes: c6eabbab359c ("drm/v3d: Add DRM_IOCTL_V3D_PERFMON_SET_GLOBAL")
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Link: https://patch.msgid.link/20260531-v3d-perfmon-lifetime-v2-1-60ed4485a203@igalia.com
Signed-off-by: Maíra Canal <mcanal@igalia.com>

1 files changed, 19 insertions, 5 deletions

diff --git a/drivers/gpu/drm/v3d/v3d_perfmon.c b/drivers/gpu/drm/v3d/v3d_perfmon.c
index 8e0249580bba..ecfd446ff75f 100644
--- a/drivers/gpu/drm/v3d/v3d_perfmon.c
+++ b/drivers/gpu/drm/v3d/v3d_perfmon.c
@@ -309,8 +309,11 @@ static void v3d_perfmon_delete(struct v3d_file_priv *v3d_priv,
 	if (perfmon == v3d->active_perfmon)
 		v3d_perfmon_stop(v3d, perfmon, false);
 
-	/* If the global perfmon is being destroyed, set it to NULL */
-	cmpxchg(&v3d->global_perfmon, perfmon, NULL);
+	/* If the global perfmon is being destroyed, clean it and release
+	 * the reference stashed in v3d_perfmon_set_global_ioctl().
+	 */
+	if (cmpxchg(&v3d->global_perfmon, perfmon, NULL) == perfmon)
+		v3d_perfmon_put(perfmon);
 
 	v3d_perfmon_put(perfmon);
 }
@@ -461,16 +464,27 @@ int v3d_perfmon_set_global_ioctl(struct drm_device *dev, void *data,
 
 	/* If the request is to clear the global performance monitor */
 	if (req->flags & DRM_V3D_PERFMON_CLEAR_GLOBAL) {
-		if (!v3d->global_perfmon)
+		struct v3d_perfmon *old;
+
+		/* DRM_V3D_PERFMON_CLEAR_GLOBAL doesn't check if
+		 * v3d->global_perfmon == perfmon. Therefore, there
+		 * is no need to keep perfmon's reference.
+		 */
+		v3d_perfmon_put(perfmon);
+
+		old = xchg(&v3d->global_perfmon, NULL);
+		if (!old)
 			return -EINVAL;
 
-		xchg(&v3d->global_perfmon, NULL);
+		v3d_perfmon_put(old);
 
 		return 0;
 	}
 
-	if (cmpxchg(&v3d->global_perfmon, NULL, perfmon))
+	if (cmpxchg(&v3d->global_perfmon, NULL, perfmon)) {
+		v3d_perfmon_put(perfmon);
 		return -EBUSY;
+	}
 
 	return 0;
 }