[PATCH v3] f2fs: Fix indefinite loop in f2fs_gc()

From: Sahitya Tummala
Date: Wed Aug 07 2019 - 04:52:28 EST


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.

Signed-off-by: Sahitya Tummala <stummala@xxxxxxxxxxxxxx>
---
v3: address Chao's comments and also add logic to clear invalid_segmap

fs/f2fs/gc.c | 25 +++++++++++++++++++++++--
fs/f2fs/segment.c | 10 +++++++++-
fs/f2fs/segment.h | 3 +++
3 files changed, 35 insertions(+), 3 deletions(-)

diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index 8974672..f7b9602 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -382,6 +382,14 @@ static int get_victim_by_default(struct f2fs_sb_info *sbi,
nsearched++;
}

+ /*
+ * 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;
+
secno = GET_SEC_FROM_SEG(sbi, segno);

if (sec_usage_check(sbi, secno))
@@ -602,8 +610,13 @@ 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;
+ struct sit_info *sit_i = SIT_I(sbi);
+
+ 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 +640,16 @@ 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) {
+ 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);
+ }
+ }
return false;
+ }
return true;
}

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index a661ac3..c3ba9e7 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -806,6 +806,7 @@ 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);
+ struct sit_info *sit_i = SIT_I(sbi);

if (test_and_clear_bit(segno, dirty_i->dirty_segmap[dirty_type]))
dirty_i->nr_dirty[dirty_type]--;
@@ -817,9 +818,11 @@ 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);
+ clear_bit(segno, sit_i->invalid_segmap);
+ }
}
}

@@ -4017,6 +4020,10 @@ static int build_sit_info(struct f2fs_sb_info *sbi)
return -ENOMEM;
#endif

+ sit_i->invalid_segmap = f2fs_kvzalloc(sbi, bitmap_size, GFP_KERNEL);
+ if (!sit_i->invalid_segmap)
+ return -ENOMEM;
+
/* init SIT information */
sit_i->s_ops = &default_salloc_ops;

@@ -4518,6 +4525,7 @@ static void destroy_sit_info(struct f2fs_sb_info *sbi)
#ifdef CONFIG_F2FS_CHECK_FS
kvfree(sit_i->sit_bitmap_mir);
#endif
+ kvfree(sit_i->invalid_segmap);
kvfree(sit_i);
}

diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
index b746028..3918155c 100644
--- a/fs/f2fs/segment.h
+++ b/fs/f2fs/segment.h
@@ -246,6 +246,9 @@ struct sit_info {
unsigned long long min_mtime; /* min. modification time */
unsigned long long max_mtime; /* max. modification time */

+ /* bitmap of segments to be ignored by GC in case of errors */
+ unsigned long *invalid_segmap;
+
unsigned int last_victim[MAX_GC_POLICY]; /* last victim segment # */
};

--
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