f2fs: don't stop GC if GC is contended

Let's do GC as much as possible, while gc_urgent is set.
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/gc.c

@@ -76,14 +76,15 @@ static int gc_thread_func(void *data)
 		 * invalidated soon after by user update or deletion.
 		 * So, I'd like to wait some time to collect dirty segments.
 		 */
-		if (!mutex_trylock(&sbi->gc_mutex))
-			goto next;
-
 		if (gc_th->gc_urgent) {
 			wait_ms = gc_th->urgent_sleep_time;
+			mutex_lock(&sbi->gc_mutex);
 			goto do_gc;
 		}
 
+		if (!mutex_trylock(&sbi->gc_mutex))
+			goto next;
+
 		if (!is_idle(sbi)) {
 			increase_sleep_time(gc_th, &wait_ms);
 			mutex_unlock(&sbi->gc_mutex);