f2fs: stop GC when the victim becomes fully valid

We must stop GC, once the segment becomes fully valid. Otherwise, it can
produce another dirty segments by moving valid blocks in the segment partially.

Ramon hit no free segment panic sometimes and saw this case happens when
validating reliable file pinning feature.

Signed-off-by: Ramon Pantin <pantin@google.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/gc.c

@@ -1012,8 +1012,14 @@ next_step:
 		block_t start_bidx;
 		nid_t nid = le32_to_cpu(entry->nid);
 
-		/* stop BG_GC if there is not enough free sections. */
-		if (gc_type == BG_GC && has_not_enough_free_secs(sbi, 0, 0))
+		/*
+		 * stop BG_GC if there is not enough free sections.
+		 * Or, stop GC if the segment becomes fully valid caused by
+		 * race condition along with SSR block allocation.
+		 */
+		if ((gc_type == BG_GC && has_not_enough_free_secs(sbi, 0, 0)) ||
+				get_valid_blocks(sbi, segno, false) ==
+							sbi->blocks_per_seg)
 			return submitted;
 
 		if (check_valid_map(sbi, segno, off) == 0)