linux-kernel - Re: [PATCH] f2fs: fix to wait IO writeback in __revoke_inmem

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Date:   Thu, 26 Apr 2018 09:48:17 -0600
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <yuchao0@...wei.com>
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, chao@...nel.org
Subject: Re: [PATCH] f2fs: fix to wait IO writeback in __revoke_inmem_pages()

On 04/26, Chao Yu wrote:
> Thread A				Thread B
> - f2fs_ioc_commit_atomic_write
>  - commit_inmem_pages
>   - f2fs_submit_merged_write_cond
>   : write data
> 					- write_checkpoint
> 					 - do_checkpoint
> 					 : commit all node within CP
> 					 -> SPO
>   - f2fs_do_sync_file
>    - file_write_and_wait_range
>    : wait data writeback
> 
> In above race condition, data/node can be flushed in reversed order when
> coming a checkpoint before f2fs_do_sync_file, after SPOR, it results in
> atomic written data being corrupted.

Wait, what is the problem here? Thread B could succeed checkpoint, there is
no problem. If it fails, there is no fsync mark where we can recover it, so
we can just ignore the last written data as nothing.

> 
> This patch adds f2fs_wait_on_page_writeback in __revoke_inmem_pages() to
> keep data and node of atomic file being flushed orderly.
> 
> Signed-off-by: Chao Yu <yuchao0@...wei.com>
> ---
>  fs/f2fs/file.c    | 4 ++++
>  fs/f2fs/segment.c | 3 +++
>  2 files changed, 7 insertions(+)
> 
> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> index be7578774a47..a352804af244 100644
> --- a/fs/f2fs/file.c
> +++ b/fs/f2fs/file.c
> @@ -217,6 +217,9 @@ static int f2fs_do_sync_file(struct file *file, loff_t start, loff_t end,
>  
>  	trace_f2fs_sync_file_enter(inode);
>  
> +	if (atomic)
> +		goto write_done;
> +
>  	/* if fdatasync is triggered, let's do in-place-update */
>  	if (datasync || get_dirty_pages(inode) <= SM_I(sbi)->min_fsync_blocks)
>  		set_inode_flag(inode, FI_NEED_IPU);
> @@ -228,6 +231,7 @@ static int f2fs_do_sync_file(struct file *file, loff_t start, loff_t end,
>  		return ret;
>  	}
>  
> +write_done:
>  	/* if the inode is dirty, let's recover all the time */
>  	if (!f2fs_skip_inode_update(inode, datasync)) {
>  		f2fs_write_inode(inode, NULL);
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index 584483426584..9ca3d0a43d93 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -230,6 +230,8 @@ static int __revoke_inmem_pages(struct inode *inode,
>  
>  		lock_page(page);
>  
> +		f2fs_wait_on_page_writeback(page, DATA, true);
> +
>  		if (recover) {
>  			struct dnode_of_data dn;
>  			struct node_info ni;
> @@ -415,6 +417,7 @@ static int __commit_inmem_pages(struct inode *inode)
>  		/* drop all uncommitted pages */
>  		__revoke_inmem_pages(inode, &fi->inmem_pages, true, false);
>  	} else {
> +		/* wait all committed IOs writeback and release them from list */
>  		__revoke_inmem_pages(inode, &revoke_list, false, false);
>  	}
>  
> -- 
> 2.15.0.55.gc2ece9dc4de6