mm/damon/sysfs: do not ignore callback's return value in damon_sysfs_damon_call()

The callback return value is ignored in damon_sysfs_damon_call(), which
means that it is not possible to detect invalid user input when writing
commands such as 'commit' to
/sys/kernel/mm/damon/admin/kdamonds/<K>/state.  Fix it.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: f64539d ("mm/damon/sysfs: use damon_call() for update_schemes_stats")
Signed-off-by: Akinobu Mita <[email protected]>
Reviewed-by: SeongJae Park <[email protected]>
Cc: <[email protected]>	[6.14+]
Signed-off-by: Andrew Morton <[email protected]>

Author: mita

mm/damon/sysfs.c

@@ -1592,12 +1592,14 @@ static int damon_sysfs_damon_call(int (*fn)(void *data),
 		struct damon_sysfs_kdamond *kdamond)
 {
 	struct damon_call_control call_control = {};
+	int err;
 
 	if (!kdamond->damon_ctx)
 		return -EINVAL;
 	call_control.fn = fn;
 	call_control.data = kdamond;
-	return damon_call(kdamond->damon_ctx, &call_control);
+	err = damon_call(kdamond->damon_ctx, &call_control);
+	return err ? err : call_control.return_code;
 }
 
 struct damon_sysfs_schemes_walk_data {