Re: [PATCH] f2fs: fix to wait IO writeback in __revoke_inmem_pages()

[Chao Yu]

On 2018/5/8 4:46, Jaegeuk Kim wrote:
> On 04/27, 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
> 
> How about, in block_operations(),
> 
> 	down_read_trylock(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> 	if (fail)
> 		wait_on_all_pages_writeback(F2FS_WB_DATA);
> 	else
> 		up_read(&F2FS_I(inode)->i_gc_rwsem[WRITE]);

I sent one patch for that, could you check it?

Adding wait_on_all_pages_writeback in block_operations() can make checkpoint()
wait pages writeback one more time, which break IO flow, so what's your concern
here?

Thanks,

> 
> 
>> 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@xxxxxxxxxx>
>>>>>> ---
>>>>>>  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
>>>
>>> .
>>>
> 
> .
>