Re: [PATCH v2] staging: erofs: fix an error handling in erofs_readdir()

[Gao Xiang]

On Sat, Aug 17, 2019 at 07:53:39PM -0700, Matthew Wilcox wrote:
> On Sun, Aug 18, 2019 at 10:32:45AM +0800, Gao Xiang wrote:
> > On Sat, Aug 17, 2019 at 07:20:55PM -0700, Matthew Wilcox wrote:
> > > On Sun, Aug 18, 2019 at 09:56:31AM +0800, Gao Xiang wrote:
> > > > @@ -82,8 +82,12 @@ static int erofs_readdir(struct file *f, struct dir_context *ctx)
> > > >  		unsigned int nameoff, maxsize;
> > > >  
> > > >  		dentry_page = read_mapping_page(mapping, i, NULL);
> > > > -		if (IS_ERR(dentry_page))
> > > > -			continue;
> > > > +		if (IS_ERR(dentry_page)) {
> > > > +			errln("fail to readdir of logical block %u of nid %llu",
> > > > +			      i, EROFS_V(dir)->nid);
> > > > +			err = PTR_ERR(dentry_page);
> > > > +			break;
> > > 
> > > I don't think you want to use the errno that came back from
> > > read_mapping_page() (which is, I think, always going to be -EIO).
> > > Rather you want -EFSCORRUPTED, at least if I understand the recent
> > > patches to ext2/ext4/f2fs/xfs/...
> > 
> > Thanks for your reply and noticing this. :)
> > 
> > Yes, as I talked with you about read_mapping_page() in a xfs related
> > topic earlier, I think I fully understand what returns here.
> > 
> > I actually had some concern about that before sending out this patch.
> > You know the status is
> >    PG_uptodate is not set and PG_error is set here.
> > 
> > But we cannot know it is actually a disk read error or due to
> > corrupted images (due to lack of page flags or some status, and
> > I think it could be a waste of page structure space for such
> > corrupted image or disk error)...
> > 
> > And some people also like propagate errors from insiders...
> > (and they could argue about err = -EFSCORRUPTED as well..)
> > 
> > I'd like hear your suggestion about this after my words above?
> > still return -EFSCORRUPTED?
> 
> I don't think it matters whether it's due to a disk error or a corrupted
> image.  We can't read the directory entry, so we should probably return
> -EFSCORRUPTED.  Thinking about it some more, read_mapping_page() can
> also return -ENOMEM, so it should probably look something like this:

OK, I will send the next version like what you described below.
I realized that at first but I have no tendency to return
EFSCORRUPTED or EIO here.

Thanks,
Gao Xiang

> 
> 		err = 0;
> 		if (dentry_page == ERR_PTR(-ENOMEM))
> 			err = -ENOMEM;
> 		else if (IS_ERR(dentry_page)) {
> 			errln("fail to readdir of logical block %u of nid %llu",
> 			      i, EROFS_V(dir)->nid);
> 			err = -EFSCORRUPTED;
> 		}
> 
> 		if (err)
> 			break;