[f2fs-dev] [PATCH v3] f2fs: Detect looped node chain efficiently

[f2fs-dev] [PATCH v3] f2fs: Detect looped node chain efficiently

[Chunhai Guo via Linux-f2fs-devel]

find_fsync_dnodes() detect the looped node chain by comparing the loop
counter with free blocks. While it may take tens of seconds to quit when
the free blocks are large enough. We can use Floyd's cycle detection
algorithm to make the detection more efficient.

Signed-off-by: Chunhai Guo <guochunhai@vivo.com>
---
v2 -> v3 : Reformat the code to make it more clear.
v1 -> v2 : Bail out if a looped is found in chain and do repair in fsck.
---
 fs/f2fs/recovery.c | 71 +++++++++++++++++++++++++++++++++-------------
 1 file changed, 51 insertions(+), 20 deletions(-)

diff --git a/fs/f2fs/recovery.c b/fs/f2fs/recovery.c
index 58c1a0096f7d..f0cf1538389c 100644
--- a/fs/f2fs/recovery.c
+++ b/fs/f2fs/recovery.c
@@ -360,21 +360,63 @@ static unsigned int adjust_por_ra_blocks(struct f2fs_sb_info *sbi,
 	return ra_blocks;
 }
 
+/* Detect looped node chain with Floyd's cycle detection algorithm. */
+static int sanity_check_node_chain(struct f2fs_sb_info *sbi, block_t blkaddr,
+		block_t *blkaddr_fast, bool *is_detecting)
+{
+	unsigned int ra_blocks = RECOVERY_MAX_RA_BLOCKS;
+	struct page *page = NULL;
+	int i;
+
+	if (!*is_detecting)
+		return 0;
+
+	for (i = 0; i < 2; i++) {
+		if (!f2fs_is_valid_blkaddr(sbi, *blkaddr_fast, META_POR)) {
+			*is_detecting = false;
+			return 0;
+		}
+
+		page = f2fs_get_tmp_page(sbi, *blkaddr_fast);
+		if (IS_ERR(page))
+			return PTR_ERR(page);
+
+		if (!is_recoverable_dnode(page)) {
+			f2fs_put_page(page, 1);
+			*is_detecting = false;
+			return 0;
+		}
+
+		ra_blocks = adjust_por_ra_blocks(sbi, ra_blocks, *blkaddr_fast,
+						next_blkaddr_of_node(page));
+
+		*blkaddr_fast = next_blkaddr_of_node(page);
+		f2fs_put_page(page, 1);
+
+		f2fs_ra_meta_pages_cond(sbi, *blkaddr_fast, ra_blocks);
+	}
+
+	if (*blkaddr_fast == blkaddr) {
+		f2fs_notice(sbi, "%s: Detect looped node chain on blkaddr:%u."
+				" Run fsck to fix it.", __func__, blkaddr);
+		return -EINVAL;
+	}
+	return 0;
+}
+
 static int find_fsync_dnodes(struct f2fs_sb_info *sbi, struct list_head *head,
 				bool check_only)
 {
 	struct curseg_info *curseg;
 	struct page *page = NULL;
-	block_t blkaddr;
-	unsigned int loop_cnt = 0;
-	unsigned int ra_blocks = RECOVERY_MAX_RA_BLOCKS;
-	unsigned int free_blocks = MAIN_SEGS(sbi) * sbi->blocks_per_seg -
-						valid_user_blocks(sbi);
+	block_t blkaddr, blkaddr_fast;
+	bool is_detecting = true;
 	int err = 0;
 
 	/* get node pages in the current segment */
 	curseg = CURSEG_I(sbi, CURSEG_WARM_NODE);
 	blkaddr = NEXT_FREE_BLKADDR(sbi, curseg);
+	blkaddr_fast = blkaddr;
 
 	while (1) {
 		struct fsync_inode_entry *entry;
@@ -431,25 +473,14 @@ static int find_fsync_dnodes(struct f2fs_sb_info *sbi, struct list_head *head,
 		if (IS_INODE(page) && is_dent_dnode(page))
 			entry->last_dentry = blkaddr;
 next:
-		/* sanity check in order to detect looped node chain */
-		if (++loop_cnt >= free_blocks ||
-			blkaddr == next_blkaddr_of_node(page)) {
-			f2fs_notice(sbi, "%s: detect looped node chain, blkaddr:%u, next:%u",
-				    __func__, blkaddr,
-				    next_blkaddr_of_node(page));
-			f2fs_put_page(page, 1);
-			err = -EINVAL;
-			break;
-		}
-
-		ra_blocks = adjust_por_ra_blocks(sbi, ra_blocks, blkaddr,
-						next_blkaddr_of_node(page));
-
 		/* check next segment */
 		blkaddr = next_blkaddr_of_node(page);
 		f2fs_put_page(page, 1);
 
-		f2fs_ra_meta_pages_cond(sbi, blkaddr, ra_blocks);
+		err = sanity_check_node_chain(sbi, blkaddr, &blkaddr_fast,
+				&is_detecting);
+		if (err)
+			break;
 	}
 	return err;
 }
-- 
2.25.1



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Re: [f2fs-dev] [PATCH v3] f2fs: Detect looped node chain efficiently

[Chao Yu]

On 2023/5/28 1:06, Chunhai Guo wrote:
> find_fsync_dnodes() detect the looped node chain by comparing the loop
> counter with free blocks. While it may take tens of seconds to quit when
> the free blocks are large enough. We can use Floyd's cycle detection
> algorithm to make the detection more efficient.
> 
> Signed-off-by: Chunhai Guo <guochunhai@vivo.com>

Reviewed-by: Chao Yu <chao@kernel.org>

Thanks,


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Re: [f2fs-dev] [PATCH v3] f2fs: Detect looped node chain efficiently

[patchwork-bot+f2fs]

Hello:

This patch was applied to jaegeuk/f2fs.git (dev)
by Jaegeuk Kim <jaegeuk@kernel.org>:

On Sun, 28 May 2023 01:06:40 +0800 you wrote:
> find_fsync_dnodes() detect the looped node chain by comparing the loop
> counter with free blocks. While it may take tens of seconds to quit when
> the free blocks are large enough. We can use Floyd's cycle detection
> algorithm to make the detection more efficient.
> 
> Signed-off-by: Chunhai Guo <guochunhai@vivo.com>
> 
> [...]

Here is the summary with links:
  - [f2fs-dev,v3] f2fs: Detect looped node chain efficiently
    https://git.kernel.org/jaegeuk/f2fs/c/a97c229c68ae

You are awesome, thank you!
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