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Date:   Mon, 17 Sep 2018 18:04:42 -0700
From:   Jaegeuk Kim <jaegeuk@kernel.org>
To:     Chao Yu <chao@kernel.org>
Cc:     linux-f2fs-devel@lists.sourceforge.net,
        linux-kernel@vger.kernel.org, Chao Yu <yuchao0@huawei.com>
Subject: Re: [PATCH v3] f2fs: submit cached bio to avoid endless PageWriteback
Message-ID: <20180918010442.GA79604@jaegeuk-macbookpro.roam.corp.google.com>
References: <20180912234053.8761-1-chao@kernel.org>
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On 09/13, Chao Yu wrote:
> From: Chao Yu <yuchao0@huawei.com>
> 
> 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@huawei.com>
> ---
> v3:
> clean up codes suggested by Jaegeuk.
>  fs/f2fs/f2fs.h |  2 +-
>  fs/f2fs/gc.c   | 71 +++++++++++++++++++++++++++++++++++---------------
>  fs/f2fs/node.c | 13 ++++++---
>  3 files changed, 61 insertions(+), 25 deletions(-)
> 
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index b676b82312e0..917b2ca76aac 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -2869,7 +2869,7 @@ struct page *f2fs_new_node_page(struct dnode_of_data *dn, unsigned int ofs);
>  void f2fs_ra_node_page(struct f2fs_sb_info *sbi, nid_t nid);
>  struct page *f2fs_get_node_page(struct f2fs_sb_info *sbi, pgoff_t nid);
>  struct page *f2fs_get_node_page_ra(struct page *parent, int start);
> -void f2fs_move_node_page(struct page *node_page, int gc_type);
> +int f2fs_move_node_page(struct page *node_page, int gc_type);
>  int f2fs_fsync_node_pages(struct f2fs_sb_info *sbi, struct inode *inode,
>  			struct writeback_control *wbc, bool atomic,
>  			unsigned int *seq_id);
> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> index a4c1a419611d..f57622cfe058 100644
> --- a/fs/f2fs/gc.c
> +++ b/fs/f2fs/gc.c
> @@ -461,7 +461,7 @@ static int check_valid_map(struct f2fs_sb_info *sbi,
>   * On validity, copy that node with cold status, otherwise (invalid node)
>   * ignore that.
>   */
> -static void gc_node_segment(struct f2fs_sb_info *sbi,
> +static int gc_node_segment(struct f2fs_sb_info *sbi,
>  		struct f2fs_summary *sum, unsigned int segno, int gc_type)
>  {
>  	struct f2fs_summary *entry;
> @@ -469,6 +469,7 @@ static void gc_node_segment(struct f2fs_sb_info *sbi,
>  	int off;
>  	int phase = 0;
>  	bool fggc = (gc_type == FG_GC);
> +	int submitted = 0;
>  
>  	start_addr = START_BLOCK(sbi, segno);
>  
> @@ -482,10 +483,11 @@ static void gc_node_segment(struct f2fs_sb_info *sbi,
>  		nid_t nid = le32_to_cpu(entry->nid);
>  		struct page *node_page;
>  		struct node_info ni;
> +		int err;
>  
>  		/* 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;
> @@ -522,7 +524,9 @@ static void gc_node_segment(struct f2fs_sb_info *sbi,
>  			continue;
>  		}
>  
> -		f2fs_move_node_page(node_page, gc_type);
> +		err = f2fs_move_node_page(node_page, gc_type);
> +		if (!err && gc_type == FG_GC)
> +			submitted++;
>  		stat_inc_node_blk_count(sbi, 1, gc_type);
>  	}
>  
> @@ -531,6 +535,7 @@ static void gc_node_segment(struct f2fs_sb_info *sbi,
>  
>  	if (fggc)
>  		atomic_dec(&sbi->wb_sync_req[NODE]);
> +	return submitted;
>  }
>  
>  /*
> @@ -666,7 +671,7 @@ 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)

We don't need to submit IOs in this case.

>  {
>  	struct f2fs_io_info fio = {
> @@ -685,25 +690,29 @@ 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;
>  	}
>  
> @@ -714,6 +723,7 @@ 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;
>  	}
>  
> @@ -796,6 +806,7 @@ 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;
> @@ -819,34 +830,42 @@ 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,
> +static int move_data_page(struct inode *inode, block_t bidx, int gc_type,
>  							unsigned int segno, int off)
>  {
>  	struct page *page;
> +	int err = 0;
>  
>  	page = f2fs_get_lock_data_page(inode, bidx, true);
>  	if (IS_ERR(page))
> -		return;
> +		return PTR_ERR(page);
>  
> -	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)) {
>  		if (gc_type == FG_GC)
>  			f2fs_pin_file_control(inode, true);
> +		err = -EAGAIN;
>  		goto out;
>  	}
>  
>  	if (gc_type == BG_GC) {
> -		if (PageWriteback(page))
> +		if (PageWriteback(page)) {
> +			err = -EAGAIN;
>  			goto out;
> +		}
>  		set_page_dirty(page);
>  		set_cold_data(page);
>  	} else {
> @@ -864,7 +883,6 @@ static void move_data_page(struct inode *inode, block_t bidx, int gc_type,
>  			.io_type = FS_GC_DATA_IO,
>  		};
>  		bool is_dirty = PageDirty(page);
> -		int err;
>  
>  retry:
>  		set_page_dirty(page);
> @@ -889,6 +907,7 @@ static void move_data_page(struct inode *inode, block_t bidx, int gc_type,
>  	}
>  out:
>  	f2fs_put_page(page, 1);
> +	return err;
>  }
>  
>  /*
> @@ -898,7 +917,7 @@ 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;
> @@ -906,6 +925,7 @@ 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);
>  
> @@ -922,7 +942,7 @@ 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;
> @@ -994,6 +1014,7 @@ 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]))
> @@ -1013,12 +1034,16 @@ 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);
> +				err = move_data_block(inode, start_bidx,
> +							gc_type, segno, off);
>  			else
> -				move_data_page(inode, start_bidx, gc_type,
> +				err = move_data_page(inode, start_bidx, gc_type,
>  								segno, off);
>  
> +			if (!err && (gc_type == FG_GC ||
> +					f2fs_post_read_required(inode)))
> +				submitted++;
> +
>  			if (locked) {
>  				up_write(&fi->i_gc_rwsem[WRITE]);
>  				up_write(&fi->i_gc_rwsem[READ]);
> @@ -1030,6 +1055,8 @@ 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,
> @@ -1057,6 +1084,7 @@ static int do_garbage_collect(struct f2fs_sb_info *sbi,
>  	int seg_freed = 0;
>  	unsigned char type = IS_DATASEG(get_seg_entry(sbi, segno)->type) ?
>  						SUM_TYPE_DATA : SUM_TYPE_NODE;
> +	int submitted = 0;
>  
>  	/* readahead multi ssa blocks those have contiguous address */
>  	if (sbi->segs_per_sec > 1)
> @@ -1100,10 +1128,11 @@ static int do_garbage_collect(struct f2fs_sb_info *sbi,
>  		 *                                  - lock_page(sum_page)
>  		 */
>  		if (type == SUM_TYPE_NODE)
> -			gc_node_segment(sbi, sum->entries, segno, gc_type);
> -		else
> -			gc_data_segment(sbi, sum->entries, gc_list, segno,
> +			submitted += gc_node_segment(sbi, sum->entries, segno,
>  								gc_type);
> +		else
> +			submitted += gc_data_segment(sbi, sum->entries, gc_list,
> +							segno, gc_type);
>  
>  		stat_inc_seg_count(sbi, type, gc_type);
>  
> @@ -1114,7 +1143,7 @@ static int do_garbage_collect(struct f2fs_sb_info *sbi,
>  		f2fs_put_page(sum_page, 0);
>  	}
>  
> -	if (gc_type == FG_GC)
> +	if (submitted)
>  		f2fs_submit_merged_write(sbi,
>  				(type == SUM_TYPE_NODE) ? NODE : DATA);
>  
> diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
> index fa2381c0bc47..214dd6326b4b 100644
> --- a/fs/f2fs/node.c
> +++ b/fs/f2fs/node.c
> @@ -1584,8 +1584,10 @@ static int __write_node_page(struct page *page, bool atomic, bool *submitted,
>  	return AOP_WRITEPAGE_ACTIVATE;
>  }
>  
> -void f2fs_move_node_page(struct page *node_page, int gc_type)
> +int f2fs_move_node_page(struct page *node_page, int gc_type)
>  {
> +	int err = 0;
> +
>  	if (gc_type == FG_GC) {
>  		struct writeback_control wbc = {
>  			.sync_mode = WB_SYNC_ALL,
> @@ -1597,12 +1599,16 @@ void f2fs_move_node_page(struct page *node_page, int gc_type)
>  		f2fs_wait_on_page_writeback(node_page, NODE, true);
>  
>  		f2fs_bug_on(F2FS_P_SB(node_page), PageWriteback(node_page));
> -		if (!clear_page_dirty_for_io(node_page))
> +		if (!clear_page_dirty_for_io(node_page)) {
> +			err = -EAGAIN;
>  			goto out_page;
> +		}
>  
>  		if (__write_node_page(node_page, false, NULL,
> -					&wbc, false, FS_GC_NODE_IO, NULL))
> +					&wbc, false, FS_GC_NODE_IO, NULL)) {
> +			err = -EAGAIN;
>  			unlock_page(node_page);
> +		}
>  		goto release_page;
>  	} else {
>  		/* set page dirty and write it */
> @@ -1613,6 +1619,7 @@ void f2fs_move_node_page(struct page *node_page, int gc_type)
>  	unlock_page(node_page);
>  release_page:
>  	f2fs_put_page(node_page, 0);
> +	return err;
>  }
>  
>  static int f2fs_write_node_page(struct page *page,
> -- 
> 2.18.0