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Date: Thu, 12 Oct 2023 16:27:55 +0100
From: Matthew Wilcox <willy@infradead.org>
To: Dan Carpenter <dan.carpenter@linaro.org>
Cc: gfs2@lists.linux.dev
Subject: Re: [bug report] gfs2: Convert gfs2_jhead_process_page() to use a
 folio
Message-ID: <ZSgQe27OCfUpmsbS@casper.infradead.org>
References: <fb027038-46ee-49fa-be1f-28926e7e2387@moroto.mountain>
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In-Reply-To: <fb027038-46ee-49fa-be1f-28926e7e2387@moroto.mountain>

On Thu, Oct 12, 2023 at 12:43:34PM +0300, Dan Carpenter wrote:
> Hello Matthew Wilcox (Oracle),
> 
> The patch 240159077d00: "gfs2: Convert gfs2_jhead_process_page() to
> use a folio" from May 13, 2022 (linux-next), leads to the following
> Smatch static checker warning:
> 
> 	fs/gfs2/lops.c:485 gfs2_jhead_process_page()
> 	error: 'folio' dereferencing possible ERR_PTR()
> 
> fs/gfs2/lops.c
>     469 static void gfs2_jhead_process_page(struct gfs2_jdesc *jd, unsigned long index,
>     470                                     struct gfs2_log_header_host *head,
>     471                                     bool *done)
>     472 {
>     473         struct folio *folio;
>     474 
>     475         folio = filemap_get_folio(jd->jd_inode->i_mapping, index);
> 
> Does filemap_get_folio() need to be checked for errors?

In this specific case, we know that the folio is there and will always
be returned.  See the comment on line 484.  Can I annotate this call so
that the tool knows this is a special case and doesn't warn about it?

>     476 
>     477         folio_wait_locked(folio);
>     478         if (folio_test_error(folio))
>     479                 *done = true;
>     480 
>     481         if (!*done)
>     482                 *done = gfs2_jhead_pg_srch(jd, head, &folio->page);
>     483 
>     484         /* filemap_get_folio() and the earlier grab_cache_page() */
> --> 485         folio_put_refs(folio, 2);
>     486 }
> 
> regards,
> dan carpenter