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

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Date:   Sat, 5 May 2018 13:36:39 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <chao@...nel.org>
CC:     <linux-f2fs-devel@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] f2fs: fix to wait IO writeback in __revoke_inmem_pages()

Ping,

On 2018/4/27 10:37, Chao Yu wrote:
> On 2018/4/27 0:36, Jaegeuk Kim wrote:
>> 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.
> 
> 1. thread A: commit_inmem_pages submit data into block layer, but haven't waited
> it writeback.
> 2. thread A: commit_inmem_pages update related node.
> 3. thread B: do checkpoint, flush all nodes to disk
> 4. SPOR
> 
> Then, atomic file becomes corrupted since nodes is flushed before data.
> 
> Thanks,
> 
>>
>>>
>>> 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
>>
>> .
>>
> 
> 
> .
>