Re: [PATCH] f2fs: fix to truncate inline data past EOF

[Jaegeuk Kim]

Hi Chao,

On Tue, Mar 10, 2015 at 10:02:46AM +0800, Chao Yu wrote:
> Hi Jaegeuk,
> 

[snip]

> > > > +static int truncate_partial_data_page(struct inode *inode, u64 from, bool force)
> > > >  {
> > > >  	unsigned offset = from & (PAGE_CACHE_SIZE - 1);
> > > >  	struct page *page;
> > > >
> > > > -	if (!offset)
> > > > +	if (!offset && !force)
> > >
> > > We truncate on-disk inode page and #0 page separately, so IMO there is a very
> > > small chance the following issue will occur.
> > >
> > > (0 < truncated_size < MAX_INLINE_SIZE)
> > > ->f2fs_setattr
> > >   ->truncate_setsize #0 page has been truncated partially
> > >   ->f2fs_truncate
> > >     ->truncate_blocks
> > > 					invalidate #0 page by reclaimer
> > > 					update #0 page with original data in inode page by reader
> > 
> > 					truncate_setsize called truncate_pagesize.
> > 					so #0 page was truncated successfully.
> 
> Yeah, but it's partially truncating as 0 < truncated_size < MAX_INLINE_SIZE,
> After truncating, we still keep [0, truncated_size) valid data in #0 page, and
> our #0 page status is uptodate | !dirty.
> 
> So what I mean is that mm can reclaim this #0 page, then if someone else read
> the #0 page again, we will update the #0 page with original data in inode page
> since inode page haven't truncated yet.

The truncate_blocks dropped inline_data in inode page, which is modified by
this patch.
And, the cached #0 page was truncated by truncate_setsize.
Even if this page was evicted and reloaded again, the data would be filled with
the inode page having truncated inline_data.
So, it seems there is no problem.

BTW, do you mean like this scenario?

-> f2fs_setattr
 ->truncate_setsize: #0 page has been truncated partially
 ->f2fs_truncate
 					invalidate #0 page by reclaimer
 					update #0 page with original data in inode page by reader

    ->truncate_blocks
      (*)-> truncate_inline_inode
    (*)-> truncate_partial_data_page(,, force)
       find_data_page(,, force)  <- we can use *force* here.

Then, I agree that two functions as noted (*) above would be necessary.

> 
> If this happened, if we don't truncate #0 page in following code of truncate_blocks,
> we will remain the original data for user, it's wrong.
> 
> IMO, it's better to truncate inode page and #0 page together, or truncate #0 page
> in truncate_partial_data_page.
> 
> How do you think?
> 
> > 
> > >       ->truncate_inline_inode
> > >       ->truncate_partial_data_page
> > >         we will fail to truncate #0 page because we can't find valid blkaddr for
> > >         #0 page in find_data_page(,,false)
> > >
> > > How about using find_data_page(,,true) to check weather this page is update or not
> > > for this condition.
> > 
> > Oh, I realized that we don't need to call truncate_partial_data_page, since the
> > cached #0 page was truncated already. We don't care about that.
> 
> IMO, we should care about this #0 page if above example can happen.
> 
> > So, do we need to add just truncate_inline_inode() like below?
> > 
> > >
> > > >  		return 0;
> > > >
> > > >  	page = find_data_page(inode, from >> PAGE_CACHE_SHIFT, false);
> > > > @@ -489,6 +489,7 @@ int truncate_blocks(struct inode *inode, u64 from, bool lock)
> > > >  	pgoff_t free_from;
> > > >  	int count = 0, err = 0;
> > > >  	struct page *ipage;
> > > > +	bool truncate_page = false;
> > > >
> > > >  	trace_f2fs_truncate_blocks_enter(inode, from);
> > > >
> > > > @@ -504,6 +505,9 @@ int truncate_blocks(struct inode *inode, u64 from, bool lock)
> > > >  	}
> > > >
> > > >  	if (f2fs_has_inline_data(inode)) {
> > > > +		truncate_inline_inode(ipage, from);
> > > > +		set_page_dirty(ipage);
> > >
> > > If @from is the same as MAX_INLINE_DATA, we will change nothing in inode page,
> > > How about skipping set_page_dirty for inode page in this condition?
> > 
> > Agreed.
> > How about adding this in truncate_inline_inode?
> > 
> > 	if (from >= MAX_INLINE_DATA)
> > 		return;
> > 	...
> > 	set_page_dirty(ipage);
> 
> Yeah, that's good.
>  
> And What I suggest is:
> 
> bool truncate_inline_inode(struct page *ipage, u64 from)
> {
> 	/*
> 	 * we should never truncate inline data past max inline data size,
> 	 * because we always convert inline inode to normal one before
> 	 * truncating real data if new size is past max inline data size.
> 	 */
> 	f2fs_bug_on(F2FS_P_SB(ipage), from > MAX_INLINE_DATA);
> 
> 	if (from == MAX_INLINE_DATA)

	if (from >= MAX_INLINE_DATA)  to handle when f2fs_bug_on is bypassed.

> 		return false;
> 	...
> 	return true;
> }
> 
> in truncate_blocks()
> 
>  	if (f2fs_has_inline_data(inode)) {
> 		if (truncate_inline_inode(ipage, from))
> 			set_page_dirty(ipage);
> 
> So by this way, we can distinguish between a bug and invalid truncating in
> truncate_inline_inode, and also we can avoid unneeded set_dirty_page for inode
> page in other call path.

Ok, it's not a big deal.

Thanks,

> 
> How do you think of this?
> 
> > 
> > Thanks,
> > 
> > Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> > ---
> >  fs/f2fs/f2fs.h   |  1 +
> >  fs/f2fs/file.c   |  1 +
> >  fs/f2fs/inline.c | 16 +++++++++++-----
> >  3 files changed, 13 insertions(+), 5 deletions(-)
> > 
> > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> > index 511d6cd..5cd3a2f 100644
> > --- a/fs/f2fs/f2fs.h
> > +++ b/fs/f2fs/f2fs.h
> > @@ -1754,6 +1754,7 @@ extern struct kmem_cache *inode_entry_slab;
> >   */
> >  bool f2fs_may_inline(struct inode *);
> >  void read_inline_data(struct page *, struct page *);
> > +void truncate_inline_inode(struct page *, u64);
> >  int f2fs_read_inline_data(struct inode *, struct page *);
> >  int f2fs_convert_inline_page(struct dnode_of_data *, struct page *);
> >  int f2fs_convert_inline_inode(struct inode *);
> > diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> > index f1341c7..b6b6a04 100644
> > --- a/fs/f2fs/file.c
> > +++ b/fs/f2fs/file.c
> > @@ -504,6 +504,7 @@ int truncate_blocks(struct inode *inode, u64 from, bool lock)
> >  	}
> > 
> >  	if (f2fs_has_inline_data(inode)) {
> > +		truncate_inline_inode(ipage, from);
> >  		f2fs_put_page(ipage, 1);
> >  		goto out;
> >  	}
> > diff --git a/fs/f2fs/inline.c b/fs/f2fs/inline.c
> > index 4ba9732..40bbf96 100644
> > --- a/fs/f2fs/inline.c
> > +++ b/fs/f2fs/inline.c
> > @@ -50,10 +50,16 @@ void read_inline_data(struct page *page, struct page *ipage)
> >  	SetPageUptodate(page);
> >  }
> > 
> > -static void truncate_inline_data(struct page *ipage)
> > +void truncate_inline_inode(struct page *ipage, u64 from)
> >  {
> > +	void *addr = inline_data_addr(ipage);
> > +
> > +	if (from >= MAX_INLIE_DATA)
> > +		return;
> > +
> >  	f2fs_wait_on_page_writeback(ipage, NODE);
> > -	memset(inline_data_addr(ipage), 0, MAX_INLINE_DATA);
> > +	memset(addr + from, 0, MAX_INLINE_DATA - from);
> > +	set_page_dirty(ipage);
> >  }
> > 
> >  int f2fs_read_inline_data(struct inode *inode, struct page *page)
> > @@ -131,7 +137,7 @@ no_update:
> >  	set_inode_flag(F2FS_I(dn->inode), FI_APPEND_WRITE);
> > 
> >  	/* clear inline data and flag after data writeback */
> > -	truncate_inline_data(dn->inode_page);
> > +	truncate_inline_inode(dn->inode_page, 0);
> >  clear_out:
> >  	stat_dec_inline_inode(dn->inode);
> >  	f2fs_clear_inline_inode(dn->inode);
> > @@ -245,7 +251,7 @@ process_inline:
> >  	if (f2fs_has_inline_data(inode)) {
> >  		ipage = get_node_page(sbi, inode->i_ino);
> >  		f2fs_bug_on(sbi, IS_ERR(ipage));
> > -		truncate_inline_data(ipage);
> > +		truncate_inline_inode(ipage, 0);
> >  		f2fs_clear_inline_inode(inode);
> >  		update_inode(inode, ipage);
> >  		f2fs_put_page(ipage, 1);
> > @@ -363,7 +369,7 @@ static int f2fs_convert_inline_dir(struct inode *dir, struct page *ipage,
> >  	set_page_dirty(page);
> > 
> >  	/* clear inline dir and flag after data writeback */
> > -	truncate_inline_data(ipage);
> > +	truncate_inline_inode(ipage, 0);
> > 
> >  	stat_dec_inline_dir(dir);
> >  	clear_inode_flag(F2FS_I(dir), FI_INLINE_DENTRY);
> > --
> > 2.1.1
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