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Date:   Tue, 6 Jun 2023 13:32:43 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Richard Weinberger <richard@nod.at>
Cc:     linux-mtd <linux-mtd@lists.infradead.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH 4/4] ubifs: Convert do_writepage() to take a folio
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On Tue, Jun 06, 2023 at 08:13:55AM +0200, Richard Weinberger wrote:
> Matthew,
> 
> ----- Ursprüngliche Mail -----
> > Von: "Matthew Wilcox" <willy@infradead.org>
> > len is folio_size(), which is not 0.
> > 
> >        len = offset_in_folio(folio, i_size);
> 
> offset_in_folio(folio, i_size) can give 0.

Oh!  There is a bug, because it shouldn't get here!

        /* Is the folio fully inside i_size? */
        if (folio_pos(folio) + len < i_size) {

should be:

        /* Is the folio fully inside i_size? */
        if (folio_pos(folio) + len <= i_size) {

right?  Consider a file with i_size 4096.  its single-page folio will
have a pos of 0 and a length of 4096.  so it should be written back by
the first call to do_writepage(), not the case where the folio straddles
i_size.