[PATCH v4] f2fs: Fix indefinite loop in f2fs_gc()

[Sahitya Tummala]

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@xxxxxxxxxxxxxx>
---
v4: Cover all logic with CONFIG_F2FS_CHECK_FS

 fs/f2fs/gc.c      | 31 +++++++++++++++++++++++++++++--
 fs/f2fs/segment.c | 14 +++++++++++++-
 fs/f2fs/segment.h |  3 +++
 3 files changed, 45 insertions(+), 3 deletions(-)

diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index 8974672..cbcacbd 100644
--- a/fs/f2fs/gc.c
+++ b/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))
@@ -602,8 +612,15 @@ static bool is_alive(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
 {
 	struct page *node_page;
 	nid_t nid;
-	unsigned int ofs_in_node;
+	unsigned int ofs_in_node, segno;
 	block_t source_blkaddr;
+	unsigned long offset;
+#ifdef CONFIG_F2FS_CHECK_FS
+	struct sit_info *sit_i = SIT_I(sbi);
+#endif
+
+	segno = GET_SEGNO(sbi, blkaddr);
+	offset = GET_BLKOFF_FROM_SEG0(sbi, blkaddr);
 
 	nid = le32_to_cpu(sum->nid);
 	ofs_in_node = le16_to_cpu(sum->ofs_in_node);
@@ -627,8 +644,18 @@ 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
+		if (unlikely(check_valid_map(sbi, segno, offset))) {
+			if (!test_and_set_bit(segno, sit_i->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;
 }
 
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index a661ac3..ee795b1 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -806,6 +806,9 @@ static void __remove_dirty_segment(struct f2fs_sb_info *sbi, unsigned int segno,
 		enum dirty_type dirty_type)
 {
 	struct dirty_seglist_info *dirty_i = DIRTY_I(sbi);
+#ifdef CONFIG_F2FS_CHECK_FS
+	struct sit_info *sit_i = SIT_I(sbi);
+#endif
 
 	if (test_and_clear_bit(segno, dirty_i->dirty_segmap[dirty_type]))
 		dirty_i->nr_dirty[dirty_type]--;
@@ -817,9 +820,13 @@ 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->invalid_segmap);
+#endif
+		}
 	}
 }
 
@@ -4015,6 +4022,10 @@ static int build_sit_info(struct f2fs_sb_info *sbi)
 	sit_i->sit_bitmap_mir = kmemdup(src_bitmap, bitmap_size, GFP_KERNEL);
 	if (!sit_i->sit_bitmap_mir)
 		return -ENOMEM;
+
+	sit_i->invalid_segmap = f2fs_kvzalloc(sbi, bitmap_size, GFP_KERNEL);
+	if (!sit_i->invalid_segmap)
+		return -ENOMEM;
 #endif
 
 	/* init SIT information */
@@ -4517,6 +4528,7 @@ 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);
 }
diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
index b746028..9370d53 100644
--- a/fs/f2fs/segment.h
+++ b/fs/f2fs/segment.h
@@ -229,6 +229,9 @@ 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 */
 
-- 
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