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SubjectRe: [PATCH] mm/filemap: Fix NULL pointer dereference in pagecache_get_page
On Tue, Apr 26, 2022 at 02:06:41PM -0700, Andrew Morton wrote:
> On Tue, 26 Apr 2022 13:08:08 +0100 Matthew Wilcox <willy@infradead.org> wrote:
>
> > On Tue, Apr 26, 2022 at 04:25:48PM +0800, Wan Jiabing wrote:
> > > Fix following coccicheck error:
> > > mm/folio-compat.c:128:17-21: ERROR: folio is NULL but dereferenced.
> > > folio = __filemap_get_folio(mapping, index, fgp_flags, gfp);
> > > - if ((fgp_flags & FGP_HEAD) || !folio || xa_is_value(folio))
> > > + if (!folio)
> > > + return NULL;
> > > + if ((fgp_flags & FGP_HEAD) || xa_is_value(folio))
> > > return &folio->page;
> >
> > That doesn't dereference the folio. Coccicheck is wrong.
>
> Doing
>
> return &(0->page);
>
> is a rather obscure way of doing `return NULL;'.
>
> I agree the patch doesn't fix anything, but it results in saner-looking code?

I suppose that's in the eye of the beholder? The original code makes
more sense to me. Besides, it's in the folio-compat file; nobody
should be looking at that except to figure out "What function should I
be transitioning to?"

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