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

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Message-ID: <20180426163651.GL68594@jaegeuk-macbookpro.roam.corp.google.com>
Date:   Thu, 26 Apr 2018 10:36:51 -0600
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <chao@...nel.org>
Cc:     Chao Yu <yuchao0@...wei.com>,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] f2fs: fix to wait IO writeback in __revoke_inmem_pages()

On 04/26, Chao Yu wrote:
> On 2018/4/26 23:48, Jaegeuk Kim wrote:
> > 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
> 
> Node is flushed by checkpoint before data, with reversed order, that's the problem.

What do you mean? Data should be in disk, in order to proceed checkpoint.

> 
> Thanks,
> 
> > 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