linux-ext4 - Re: [PATCH v2 29/29] ext4: Use a folio in ext4_read_merkle_tree

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Date:   Tue, 18 Apr 2023 14:08:05 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     tytso@....edu, adilger.kernel@...ger.ca,
        linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v2 29/29] ext4: Use a folio in ext4_read_merkle_tree_page

On Mon, Apr 17, 2023 at 11:50:42PM -0700, Eric Biggers wrote:
> Hi Matthew,
> 
> On Fri, Mar 24, 2023 at 06:01:29PM +0000, Matthew Wilcox (Oracle) wrote:
> > This is an implementation of fsverity_operations read_merkle_tree_page,
> > so it must still return the precise page asked for, but we can use the
> > folio API to reduce the number of conversions between folios & pages.
> > 
> > Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> > ---
> >  fs/ext4/verity.c | 14 +++++++-------
> >  1 file changed, 7 insertions(+), 7 deletions(-)
> > 
> > diff --git a/fs/ext4/verity.c b/fs/ext4/verity.c
> > index afe847c967a4..3b01247066dd 100644
> > --- a/fs/ext4/verity.c
> > +++ b/fs/ext4/verity.c
> > @@ -361,21 +361,21 @@ static struct page *ext4_read_merkle_tree_page(struct inode *inode,
> >  					       pgoff_t index,
> >  					       unsigned long num_ra_pages)
> >  {
> > -	struct page *page;
> > +	struct folio *folio;
> >  
> >  	index += ext4_verity_metadata_pos(inode) >> PAGE_SHIFT;
> >  
> > -	page = find_get_page_flags(inode->i_mapping, index, FGP_ACCESSED);
> > -	if (!page || !PageUptodate(page)) {
> > +	folio = __filemap_get_folio(inode->i_mapping, index, FGP_ACCESSED, 0);
> > +	if (!folio || !folio_test_uptodate(folio)) {
> >  		DEFINE_READAHEAD(ractl, NULL, NULL, inode->i_mapping, index);
> >  
> > -		if (page)
> > -			put_page(page);
> > +		if (folio)
> > +			folio_put(folio);
> >  		else if (num_ra_pages > 1)
> >  			page_cache_ra_unbounded(&ractl, num_ra_pages, 0);
> > -		page = read_mapping_page(inode->i_mapping, index, NULL);
> > +		folio = read_mapping_folio(inode->i_mapping, index, NULL);
> >  	}
> > -	return page;
> > +	return folio_file_page(folio, index);
> 
> This is not working at all, since it dereferences ERR_PTR(-ENOENT).  I think it
> needs:

Argh.  Christoph changed the return value of __filemap_get_folio().

>  	folio = __filemap_get_folio(inode->i_mapping, index, FGP_ACCESSED, 0);
> -	if (!folio || !folio_test_uptodate(folio)) {
> +	if (folio == ERR_PTR(-ENOENT) || !folio_test_uptodate(folio)) {

This should be "if (IS_ERR(folio) || !folio_test_uptodate(folio)) {"

But we can't carry this change in Ted's tree because it doesn't have
Christoph's change.  And we can't carry it in Andrew's tree because it
doesn't have my ext4 change.

>  		DEFINE_READAHEAD(ractl, NULL, NULL, inode->i_mapping, index);
>  
> -		if (folio)
> +		if (!IS_ERR(folio))
>  			folio_put(folio);
>  		else if (num_ra_pages > 1)
>  			page_cache_ra_unbounded(&ractl, num_ra_pages, 0);
>  		folio = read_mapping_folio(inode->i_mapping, index, NULL);
>  	}
> +	if (IS_ERR(folio))
> +		return ERR_CAST(folio);

return &folio->page;

>  	return folio_file_page(folio, index);
>  }
>