Re: [f2fs-dev] 答复: [PATCH v4] f2fs: compress: avoid unnecessary check in f2fs_prepare_compress_overwrite

[Eric Biggers <ebiggers@kernel.org>]

On Fri, May 14, 2021 at 09:15:54AM +0800, Chao Yu wrote:
> On 2021/5/14 5:17, Eric Biggers wrote:
> > On Wed, May 12, 2021 at 09:52:19AM +0800, Chao Yu wrote:
> > > On 2021/5/12 5:50, Jaegeuk Kim wrote:
> > > > On 05/11, changfengnan@vivo.com wrote:
> > > > > Hi Jaegeuk:
> > > > > 
> > > > > If there're existing clusters beyond i_size, may cause data corruption, but
> > > > > will this happen in normal? maybe some error can cause this, if i_size is
> > > > > error the data beyond size still can't handle properly.  Is there normal
> > > > > case can casue existing clusters beyond i_size?
> > > > 
> > > > We don't have a rule to sync between i_size and i_blocks.
> > > 
> > > I can't image a case that compressed cluster may cross filesize, it looks it's
> > > a bug if that happened, but I'm not sure I have considered all cases. So, I
> > > prefer to add a check condition as below, then testing w/ xfstest/por_fsstress
> > > for a while.
> > > 
> > > Subject: [PATCH] f2fs: compress: compressed cluster should not cross i_size
> > > 
> > > ---
> > >   fs/f2fs/data.c | 2 ++
> > >   1 file changed, 2 insertions(+)
> > > 
> > > diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> > > index 06d1e58d3882..9acca358d578 100644
> > > --- a/fs/f2fs/data.c
> > > +++ b/fs/f2fs/data.c
> > > @@ -3325,6 +3325,8 @@ static int f2fs_write_begin(struct file *file, struct address_space *mapping,
> > >   			err = ret;
> > >   			goto fail;
> > >   		} else if (ret) {
> > > +			f2fs_bug_on(sbi, index >=
> > > +				DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE));
> > >   			return 0;
> > >   		}
> > >   	}
> > 
> > If a file has both fs-verity and compression enabled, it can have compressed
> > clusters past i_size.
> 
> Correct, any other case we missed for a writable file? let us know.
> 
> Thanks,
> 

Well, files become read-only once fs-verity is enabled on them, but that happens
after the blocks past i_size are written in the first place.  That part still
uses ->write_begin(), ->write_end(), ->writepages(), etc.

- Eric


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