drm/vc4: Stop the active perfmon before being destroyed

Upon closing the file descriptor, the active performance monitor is not
stopped. Although all perfmons are destroyed in `vc4_perfmon_close_file()`,
the active performance monitor's pointer (`vc4->active_perfmon`) is still
retained.

If we open a new file descriptor and submit a few jobs with performance
monitors, the driver will attempt to stop the active performance monitor
using the stale pointer in `vc4->active_perfmon`. However, this pointer
is no longer valid because the previous process has already terminated,
and all performance monitors associated with it have been destroyed and
freed.

To fix this, when the active performance monitor belongs to a given
process, explicitly stop it before destroying and freeing it.

Cc: stable@vger.kernel.org # v4.17+
Cc: Boris Brezillon <bbrezillon@kernel.org>
Cc: Juan A. Suarez Romero <jasuarez@igalia.com>
Fixes: 65101d8c ("drm/vc4: Expose performance counters to userspace")
Signed-off-by: Maíra Canal <mcanal@igalia.com>
Reviewed-by: Juan A. Suarez <jasuarez@igalia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241004123817.890016-2-mcanal@igalia.com

drivers/gpu/drm/vc4/vc4_perfmon.c

@@ -116,6 +116,11 @@ void vc4_perfmon_open_file(struct vc4_file *vc4file)
 static int vc4_perfmon_idr_del(int id, void *elem, void *data)
 {
 	struct vc4_perfmon *perfmon = elem;
+	struct vc4_dev *vc4 = (struct vc4_dev *)data;
+
+	/* If the active perfmon is being destroyed, stop it first */
+	if (perfmon == vc4->active_perfmon)
+		vc4_perfmon_stop(vc4, perfmon, false);
 
 	vc4_perfmon_put(perfmon);
 
@@ -130,7 +135,7 @@ void vc4_perfmon_close_file(struct vc4_file *vc4file)
 		return;
 
 	mutex_lock(&vc4file->perfmon.lock);
-	idr_for_each(&vc4file->perfmon.idr, vc4_perfmon_idr_del, NULL);
+	idr_for_each(&vc4file->perfmon.idr, vc4_perfmon_idr_del, vc4);
 	idr_destroy(&vc4file->perfmon.idr);
 	mutex_unlock(&vc4file->perfmon.lock);
 	mutex_destroy(&vc4file->perfmon.lock);