Re: [f2fs-dev] [PATCH v8] fsck.f2fs: Detect and fix looped node chain efficiently

[Jaegeuk Kim <jaegeuk@kernel.org>]

On 06/14, Chunhai Guo wrote:
> Hi Jaegeuk,
> 
> Could you please help to confirm if this patch has been merged? I cannot see
> the patch in the dev-test or dev branch.

Thanks. Somehow it was dropped. I start to test again.

> 
> Thanks.
> 
> On 2023/5/24 10:42, 郭纯海 wrote:
> > find_fsync_inode() 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, and fix the issue by
> > filling a NULL address in the last node of the chain.
> > 
> > Below is the log we encounter on a 256GB UFS storage and it takes about
> > 25 seconds to detect looped node chain. After changing the algorithm, it
> > takes about 20ms to finish the same job.
> > 
> >      [   10.822904] fsck.f2fs: Info: version timestamp cur: 17, prev: 430
> >      [   10.822949] fsck.f2fs: [update_superblock: 762] Info: Done to
> > update superblock
> >      [   10.822953] fsck.f2fs: Info: superblock features = 1499 :
> > encrypt verity extra_attr project_quota quota_ino casefold
> >      [   10.822956] fsck.f2fs: Info: superblock encrypt level = 0, salt =
> > 00000000000000000000000000000000
> >      [   10.822960] fsck.f2fs: Info: total FS sectors = 59249811 (231444
> > MB)
> >      [   35.852827] fsck.f2fs:	detect looped node chain,
> > blkaddr:1114802, next:1114803
> >      [   35.852842] fsck.f2fs: [f2fs_do_mount:3846] record_fsync_data
> > failed
> >      [   35.856106] fsck.f2fs: fsck.f2fs terminated by exit(255)
> > 
> > Signed-off-by: Chunhai Guo <guochunhai@vivo.com>
> > ---
> > v7 -> v8 : Reformat the code to reduce indention.
> > v6 -> v7 : Correct logic error to handle is_detecting return by
> > 	find_node_blk_fast().
> > v5 -> v6 : Simplify the code by removing unnecessary retry logic.
> > v4 -> v5 : Use IS_INODE() to make the code more clear.
> > v3 -> v4 : Set c.bug_on with ASSERT_MSG() when issue is detected and fix
> > 	it only if c.fix_on is 1.
> > v2 -> v3 : Write inode with write_inode() to avoid chksum being broken.
> > v1 -> v2 : Fix looped node chain directly after it is detected.
> > ---
> >   fsck/mount.c | 127 +++++++++++++++++++++++++++++++++++++++++++++------
> >   1 file changed, 112 insertions(+), 15 deletions(-)
> > 
> > diff --git a/fsck/mount.c b/fsck/mount.c
> > index 4c7488840c7c..9d6a222a055c 100644
> > --- a/fsck/mount.c
> > +++ b/fsck/mount.c
> > @@ -3518,22 +3518,90 @@ static void destroy_fsync_dnodes(struct list_head *head)
> >   		del_fsync_inode(entry);
> >   }
> > +static int find_node_blk_fast(struct f2fs_sb_info *sbi, block_t *blkaddr_fast,
> > +		struct f2fs_node *node_blk_fast, bool *is_detecting)
> > +{
> > +	int i, err;
> > +
> > +	for (i = 0; i < 2; i++) {
> > +		if (!f2fs_is_valid_blkaddr(sbi, *blkaddr_fast, META_POR)) {
> > +			*is_detecting = false;
> > +			return 0;
> > +		}
> > +
> > +		err = dev_read_block(node_blk_fast, *blkaddr_fast);
> > +		if (err)
> > +			return err;
> > +
> > +		if (!is_recoverable_dnode(sbi, node_blk_fast)) {
> > +			*is_detecting = false;
> > +			return 0;
> > +		}
> > +
> > +		*blkaddr_fast = next_blkaddr_of_node(node_blk_fast);
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +static int loop_node_chain_fix(struct f2fs_sb_info *sbi,
> > +		block_t blkaddr_fast, struct f2fs_node *node_blk_fast,
> > +		block_t blkaddr, struct f2fs_node *node_blk)
> > +{
> > +	block_t blkaddr_entry, blkaddr_tmp;
> > +	int err;
> > +
> > +	/* find the entry point of the looped node chain */
> > +	while (blkaddr_fast != blkaddr) {
> > +		err = dev_read_block(node_blk_fast, blkaddr_fast);
> > +		if (err)
> > +			return err;
> > +		blkaddr_fast = next_blkaddr_of_node(node_blk_fast);
> > +
> > +		err = dev_read_block(node_blk, blkaddr);
> > +		if (err)
> > +			return err;
> > +		blkaddr = next_blkaddr_of_node(node_blk);
> > +	}
> > +	blkaddr_entry = blkaddr;
> > +
> > +	/* find the last node of the chain */
> > +	do {
> > +		blkaddr_tmp = blkaddr;
> > +		err = dev_read_block(node_blk, blkaddr);
> > +		if (err)
> > +			return err;
> > +		blkaddr = next_blkaddr_of_node(node_blk);
> > +	} while (blkaddr != blkaddr_entry);
> > +
> > +	/* fix the blkaddr of last node with NULL_ADDR. */
> > +	node_blk->footer.next_blkaddr = NULL_ADDR;
> > +	if (IS_INODE(node_blk))
> > +		err = write_inode(node_blk, blkaddr_tmp);
> > +	else
> > +		err = dev_write_block(node_blk, blkaddr_tmp);
> > +	if (!err)
> > +		FIX_MSG("Fix looped node chain on blkaddr %u\n",
> > +				blkaddr_tmp);
> > +	return err;
> > +}
> > +
> >   static int find_fsync_inode(struct f2fs_sb_info *sbi, struct list_head *head)
> >   {
> >   	struct curseg_info *curseg;
> > -	struct f2fs_node *node_blk;
> > -	block_t blkaddr;
> > -	unsigned int loop_cnt = 0;
> > -	unsigned int free_blocks = MAIN_SEGS(sbi) * sbi->blocks_per_seg -
> > -						sbi->total_valid_block_count;
> > +	struct f2fs_node *node_blk, *node_blk_fast;
> > +	block_t blkaddr, blkaddr_fast;
> > +	bool is_detecting = true;
> >   	int err = 0;
> > +	node_blk = calloc(F2FS_BLKSIZE, 1);
> > +	node_blk_fast = calloc(F2FS_BLKSIZE, 1);
> > +	ASSERT(node_blk && node_blk_fast);
> > +
> >   	/* get node pages in the current segment */
> >   	curseg = CURSEG_I(sbi, CURSEG_WARM_NODE);
> >   	blkaddr = NEXT_FREE_BLKADDR(sbi, curseg);
> > -
> > -	node_blk = calloc(F2FS_BLKSIZE, 1);
> > -	ASSERT(node_blk);
> > +	blkaddr_fast = blkaddr;
> >   	while (1) {
> >   		struct fsync_inode_entry *entry;
> > @@ -3564,19 +3632,48 @@ static int find_fsync_inode(struct f2fs_sb_info *sbi, struct list_head *head)
> >   		if (IS_INODE(node_blk) && is_dent_dnode(node_blk))
> >   			entry->last_dentry = blkaddr;
> >   next:
> > -		/* sanity check in order to detect looped node chain */
> > -		if (++loop_cnt >= free_blocks ||
> > -			blkaddr == next_blkaddr_of_node(node_blk)) {
> > -			MSG(0, "\tdetect looped node chain, blkaddr:%u, next:%u\n",
> > -				    blkaddr,
> > -				    next_blkaddr_of_node(node_blk));
> > +		blkaddr = next_blkaddr_of_node(node_blk);
> > +
> > +		/* Below we will detect looped node chain with Floyd's cycle
> > +		 * detection algorithm.
> > +		 */
> > +		if (!is_detecting)
> > +			continue;
> > +
> > +		err = find_node_blk_fast(sbi, &blkaddr_fast,
> > +				node_blk_fast, &is_detecting);
> > +		if (err)
> > +			break;
> > +
> > +		if (!is_detecting)
> > +			continue;
> > +
> > +		if (blkaddr_fast != blkaddr)
> > +			continue;
> > +
> > +		ASSERT_MSG("\tdetect looped node chain, blkaddr:%u\n",
> > +				blkaddr);
> > +
> > +		if (!c.fix_on) {
> >   			err = -1;
> >   			break;
> >   		}
> > -		blkaddr = next_blkaddr_of_node(node_blk);
> > +		err = loop_node_chain_fix(sbi,
> > +				NEXT_FREE_BLKADDR(sbi, curseg),
> > +				node_blk_fast, blkaddr, node_blk);
> > +		if (err)
> > +			break;
> > +
> > +		/* Since we call get_fsync_inode() to ensure there are no
> > +		 * duplicate inodes in the inode_list even if there are
> > +		 * duplicate blkaddr, we can continue running after fixing the
> > +		 * looped node chain.
> > +		 */
> > +		is_detecting = false;
> >   	}
> > +	free(node_blk_fast);
> >   	free(node_blk);
> >   	return err;
> >   }


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