Re: [PATCH] f2fs: submit cached bio to avoid endless PageWriteback

[Jaegeuk Kim]

On 09/11, Chao Yu wrote:
> When migrating encrypted block from background GC thread, we only add
> them into f2fs inner bio cache, but forget to submit the cached bio, it
> may cause potential deadlock when we are waiting page writebacked, fix
> it.
> 
> Signed-off-by: Chao Yu <yuchao0@xxxxxxxxxx>
> ---
>  fs/f2fs/gc.c | 42 +++++++++++++++++++++++++++++-------------
>  1 file changed, 29 insertions(+), 13 deletions(-)
> 
> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> index c4ea4009cf05..a2ea0d445345 100644
> --- a/fs/f2fs/gc.c
> +++ b/fs/f2fs/gc.c
> @@ -687,7 +687,7 @@ static int ra_data_block(struct inode *inode, pgoff_t index)
>   * Move data block via META_MAPPING while keeping locked data page.
>   * This can be used to move blocks, aka LBAs, directly on disk.
>   */
> -static void move_data_block(struct inode *inode, block_t bidx,
> +static int move_data_block(struct inode *inode, block_t bidx,
>  				int gc_type, unsigned int segno, int off)
>  {
>  	struct f2fs_io_info fio = {
> @@ -706,25 +706,29 @@ static void move_data_block(struct inode *inode, block_t bidx,
>  	struct node_info ni;
>  	struct page *page, *mpage;
>  	block_t newaddr;
> -	int err;
> +	int err = 0;
>  	bool lfs_mode = test_opt(fio.sbi, LFS);
>  
>  	/* do not read out */
>  	page = f2fs_grab_cache_page(inode->i_mapping, bidx, false);
>  	if (!page)
> -		return;
> +		return -ENOMEM;
>  
> -	if (!check_valid_map(F2FS_I_SB(inode), segno, off))
> +	if (!check_valid_map(F2FS_I_SB(inode), segno, off)) {
> +		err = -ENOENT;
>  		goto out;
> +	}
>  
>  	if (f2fs_is_atomic_file(inode)) {
>  		F2FS_I(inode)->i_gc_failures[GC_FAILURE_ATOMIC]++;
>  		F2FS_I_SB(inode)->skipped_atomic_files[gc_type]++;
> +		err = -EAGAIN;
>  		goto out;
>  	}
>  
>  	if (f2fs_is_pinned_file(inode)) {
>  		f2fs_pin_file_control(inode, true);
> +		err = -EAGAIN;
>  		goto out;
>  	}
>  
> @@ -735,6 +739,7 @@ static void move_data_block(struct inode *inode, block_t bidx,
>  
>  	if (unlikely(dn.data_blkaddr == NULL_ADDR)) {
>  		ClearPageUptodate(page);
> +		err = -ENOENT;
>  		goto put_out;
>  	}
>  
> @@ -817,6 +822,7 @@ static void move_data_block(struct inode *inode, block_t bidx,
>  	fio.new_blkaddr = newaddr;
>  	f2fs_submit_page_write(&fio);
>  	if (fio.retry) {
> +		err = -EAGAIN;
>  		if (PageWriteback(fio.encrypted_page))
>  			end_page_writeback(fio.encrypted_page);
>  		goto put_page_out;
> @@ -840,6 +846,8 @@ static void move_data_block(struct inode *inode, block_t bidx,
>  	f2fs_put_dnode(&dn);
>  out:
>  	f2fs_put_page(page, 1);
> +
> +	return err;
>  }
>  
>  static void move_data_page(struct inode *inode, block_t bidx, int gc_type,
> @@ -919,7 +927,7 @@ static void move_data_page(struct inode *inode, block_t bidx, int gc_type,
>   * If the parent node is not valid or the data block address is different,
>   * the victim data block is ignored.
>   */
> -static void gc_data_segment(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
> +static int gc_data_segment(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
>  		struct gc_inode_list *gc_list, unsigned int segno, int gc_type)
>  {
>  	struct super_block *sb = sbi->sb;
> @@ -927,6 +935,7 @@ static void gc_data_segment(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
>  	block_t start_addr;
>  	int off;
>  	int phase = 0;
> +	int submitted = 0;
>  
>  	start_addr = START_BLOCK(sbi, segno);
>  
> @@ -943,7 +952,7 @@ static void gc_data_segment(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
>  
>  		/* stop BG_GC if there is not enough free sections. */
>  		if (gc_type == BG_GC && has_not_enough_free_secs(sbi, 0, 0))
> -			return;
> +			return submitted;
>  
>  		if (check_valid_map(sbi, segno, off) == 0)
>  			continue;
> @@ -1015,6 +1024,7 @@ static void gc_data_segment(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
>  		if (inode) {
>  			struct f2fs_inode_info *fi = F2FS_I(inode);
>  			bool locked = false;
> +			int err;
>  
>  			if (S_ISREG(inode->i_mode)) {
>  				if (!down_write_trylock(&fi->i_gc_rwsem[READ]))
> @@ -1033,12 +1043,15 @@ static void gc_data_segment(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
>  
>  			start_bidx = f2fs_start_bidx_of_node(nofs, inode)
>  								+ ofs_in_node;
> -			if (f2fs_post_read_required(inode))
> -				move_data_block(inode, start_bidx, gc_type,
> -								segno, off);
> -			else
> +			if (f2fs_post_read_required(inode)) {
> +				err = move_data_block(inode, start_bidx,
> +							gc_type, segno, off);
> +				if (!err)
> +					submitted++;
> +			} else {
>  				move_data_page(inode, start_bidx, gc_type,
>  								segno, off);
> +			}
>  
>  			if (locked) {
>  				up_write(&fi->i_gc_rwsem[WRITE]);
> @@ -1051,6 +1064,8 @@ static void gc_data_segment(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
>  
>  	if (++phase < 5)
>  		goto next_step;
> +
> +	return submitted;
>  }
>  
>  static int __get_victim(struct f2fs_sb_info *sbi, unsigned int *victim,
> @@ -1078,6 +1093,7 @@ static int do_garbage_collect(struct f2fs_sb_info *sbi,
>  	unsigned char type = IS_DATASEG(get_seg_entry(sbi, segno)->type) ?
>  						SUM_TYPE_DATA : SUM_TYPE_NODE;
>  	unsigned int units = 0;
> +	int submitted = 0;
>  
>  	/* start segno may point to middle of section, so adjust it */
>  	if (__is_large_section(sbi))
> @@ -1136,8 +1152,8 @@ static int do_garbage_collect(struct f2fs_sb_info *sbi,
>  		if (type == SUM_TYPE_NODE)
>  			gc_node_segment(sbi, sum->entries, segno, gc_type);
>  		else
> -			gc_data_segment(sbi, sum->entries, gc_list, segno,
> -								gc_type);
> +			submitted += gc_data_segment(sbi, sum->entries, gc_list,
> +							segno, gc_type);
>  
>  		stat_inc_seg_count(sbi, type, gc_type);
>  
> @@ -1152,7 +1168,7 @@ static int do_garbage_collect(struct f2fs_sb_info *sbi,
>  		f2fs_put_page(sum_page, 0);
>  	}
>  
> -	if (gc_type == FG_GC)
> +	if (gc_type == FG_GC || submitted)

Do we need to check submitted for both of node and data? Then, we can remove
FG_GC case?

>  		f2fs_submit_merged_write(sbi,
>  				(type == SUM_TYPE_NODE) ? NODE : DATA);
>  
> -- 
> 2.18.0.rc1