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

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Date:   Mon, 7 May 2018 20:31:55 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <yuchao0@...wei.com>
Cc:     Chao Yu <chao@...nel.org>, 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 05/08, Chao Yu wrote:
> 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?

Performance. And I can see wait_on_all_pages_writeback() waits only for
F2FS_WB_CP_DATA in checkpoint()?


> 
> 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@...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
> >>>
> >>> .
> >>>
> > 
> > .
> >