f2fs: Fix indefinite loop in f2fs_gc()

Policy - Foreground GC, LFS and greedy GC mode.

Under this policy, f2fs_gc() loops forever to GC as it doesn't have
enough free segements to proceed and thus it keeps calling gc_more
for the same victim segment.  This can happen if the selected victim
segment could not be GC'd due to failed blkaddr validity check i.e.
is_alive() returns false for the blocks set in current validity map.

Fix this by keeping track of such invalid segments and skip those
segments for selection in get_victim_by_default() to avoid endless
GC loop under such error scenarios. Currently, add this logic under
CONFIG_F2FS_CHECK_FS to be able to root cause the issue in debug
version.
Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
[Jaegeuk Kim: fix wrong bitmap size]
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/gc.c

@@ -382,6 +382,16 @@ static int get_victim_by_default(struct f2fs_sb_info *sbi,
 			nsearched++;
 		}
 
+#ifdef CONFIG_F2FS_CHECK_FS
+		/*
+		 * skip selecting the invalid segno (that is failed due to block
+		 * validity check failure during GC) to avoid endless GC loop in
+		 * such cases.
+		 */
+		if (test_bit(segno, sm->invalid_segmap))
+			goto next;
+#endif
+
 		secno = GET_SEC_FROM_SEG(sbi, segno);
 
 		if (sec_usage_check(sbi, secno))
@@ -627,8 +637,21 @@ static bool is_alive(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
 	source_blkaddr = datablock_addr(NULL, node_page, ofs_in_node);
 	f2fs_put_page(node_page, 1);
 
-	if (source_blkaddr != blkaddr)
+	if (source_blkaddr != blkaddr) {
+#ifdef CONFIG_F2FS_CHECK_FS
+		unsigned int segno = GET_SEGNO(sbi, blkaddr);
+		unsigned long offset = GET_BLKOFF_FROM_SEG0(sbi, blkaddr);
+
+		if (unlikely(check_valid_map(sbi, segno, offset))) {
+			if (!test_and_set_bit(segno, SIT_I(sbi)->invalid_segmap)) {
+				f2fs_err(sbi, "mismatched blkaddr %u (source_blkaddr %u) in seg %u\n",
+						blkaddr, source_blkaddr, segno);
+				f2fs_bug_on(sbi, 1);
+			}
+		}
+#endif
 		return false;
+	}
 	return true;
 }
 

fs/f2fs/segment.c

@@ -817,9 +817,13 @@ static void __remove_dirty_segment(struct f2fs_sb_info *sbi, unsigned int segno,
 		if (test_and_clear_bit(segno, dirty_i->dirty_segmap[t]))
 			dirty_i->nr_dirty[t]--;
 
-		if (get_valid_blocks(sbi, segno, true) == 0)
+		if (get_valid_blocks(sbi, segno, true) == 0) {
 			clear_bit(GET_SEC_FROM_SEG(sbi, segno),
 						dirty_i->victim_secmap);
+#ifdef CONFIG_F2FS_CHECK_FS
+			clear_bit(segno, SIT_I(sbi)->invalid_segmap);
+#endif
+		}
 	}
 }
 
@@ -3946,7 +3950,7 @@ static int build_sit_info(struct f2fs_sb_info *sbi)
 	struct sit_info *sit_i;
 	unsigned int sit_segs, start;
 	char *src_bitmap, *bitmap;
-	unsigned int bitmap_size;
+	unsigned int bitmap_size, main_bitmap_size, sit_bitmap_size;
 
 	/* allocate memory for SIT information */
 	sit_i = f2fs_kzalloc(sbi, sizeof(struct sit_info), GFP_KERNEL);
@@ -3962,8 +3966,8 @@ static int build_sit_info(struct f2fs_sb_info *sbi)
 	if (!sit_i->sentries)
 		return -ENOMEM;
 
-	bitmap_size = f2fs_bitmap_size(MAIN_SEGS(sbi));
-	sit_i->dirty_sentries_bitmap = f2fs_kvzalloc(sbi, bitmap_size,
+	main_bitmap_size = f2fs_bitmap_size(MAIN_SEGS(sbi));
+	sit_i->dirty_sentries_bitmap = f2fs_kvzalloc(sbi, main_bitmap_size,
 								GFP_KERNEL);
 	if (!sit_i->dirty_sentries_bitmap)
 		return -ENOMEM;
@@ -4012,17 +4016,23 @@ static int build_sit_info(struct f2fs_sb_info *sbi)
 	sit_segs = le32_to_cpu(raw_super->segment_count_sit) >> 1;
 
 	/* setup SIT bitmap from ckeckpoint pack */
-	bitmap_size = __bitmap_size(sbi, SIT_BITMAP);
+	sit_bitmap_size = __bitmap_size(sbi, SIT_BITMAP);
 	src_bitmap = __bitmap_ptr(sbi, SIT_BITMAP);
 
-	sit_i->sit_bitmap = kmemdup(src_bitmap, bitmap_size, GFP_KERNEL);
+	sit_i->sit_bitmap = kmemdup(src_bitmap, sit_bitmap_size, GFP_KERNEL);
 	if (!sit_i->sit_bitmap)
 		return -ENOMEM;
 
 #ifdef CONFIG_F2FS_CHECK_FS
-	sit_i->sit_bitmap_mir = kmemdup(src_bitmap, bitmap_size, GFP_KERNEL);
+	sit_i->sit_bitmap_mir = kmemdup(src_bitmap,
+					sit_bitmap_size, GFP_KERNEL);
 	if (!sit_i->sit_bitmap_mir)
 		return -ENOMEM;
+
+	sit_i->invalid_segmap = f2fs_kvzalloc(sbi,
+					main_bitmap_size, GFP_KERNEL);
+	if (!sit_i->invalid_segmap)
+		return -ENOMEM;
 #endif
 
 	/* init SIT information */
@@ -4031,7 +4041,7 @@ static int build_sit_info(struct f2fs_sb_info *sbi)
 	sit_i->sit_base_addr = le32_to_cpu(raw_super->sit_blkaddr);
 	sit_i->sit_blocks = sit_segs << sbi->log_blocks_per_seg;
 	sit_i->written_valid_blocks = 0;
-	sit_i->bitmap_size = bitmap_size;
+	sit_i->bitmap_size = sit_bitmap_size;
 	sit_i->dirty_sentries = 0;
 	sit_i->sents_per_block = SIT_ENTRY_PER_BLOCK;
 	sit_i->elapsed_time = le64_to_cpu(sbi->ckpt->elapsed_time);
@@ -4514,6 +4524,7 @@ static void destroy_sit_info(struct f2fs_sb_info *sbi)
 	kvfree(sit_i->sit_bitmap);
 #ifdef CONFIG_F2FS_CHECK_FS
 	kvfree(sit_i->sit_bitmap_mir);
+	kvfree(sit_i->invalid_segmap);
 #endif
 	kvfree(sit_i);
 }

fs/f2fs/segment.h

@@ -230,6 +230,9 @@ struct sit_info {
 	char *sit_bitmap;		/* SIT bitmap pointer */
 #ifdef CONFIG_F2FS_CHECK_FS
 	char *sit_bitmap_mir;		/* SIT bitmap mirror */
+
+	/* bitmap of segments to be ignored by GC in case of errors */
+	unsigned long *invalid_segmap;
 #endif
 	unsigned int bitmap_size;	/* SIT bitmap size */