damon/sysfs: fix possible memleak on damon_sysfs_add_target

When damon_sysfs_add_target couldn't find proper task, New allocated
damon_target structure isn't registered yet, So, it's impossible to free
new allocated one by damon_sysfs_destroy_targets.

By calling damon_add_target as soon as allocating new target, Fix this
possible memory leak.

Link: https://lkml.kernel.org/r/20220926160611.48536-1-sj@kernel.org
Fixes: a61ea56 ("mm/damon/sysfs: link DAMON for virtual address spaces monitoring")
Signed-off-by: Levi Yun <ppbuk5246@gmail.com>
Signed-off-by: SeongJae Park <sj@kernel.org>
Reviewed-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org>	[5.17.x]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: SupremacistLevi

mm/damon/sysfs.c

@@ -2182,12 +2182,12 @@ static int damon_sysfs_add_target(struct damon_sysfs_target *sys_target,
 
 	if (!t)
 		return -ENOMEM;
+	damon_add_target(ctx, t);
 	if (damon_target_has_pid(ctx)) {
 		t->pid = find_get_pid(sys_target->pid);
 		if (!t->pid)
 			goto destroy_targets_out;
 	}
-	damon_add_target(ctx, t);
 	err = damon_sysfs_set_regions(t, sys_target->regions);
 	if (err)
 		goto destroy_targets_out;