Re: [PATCH] mm/page_alloc: do bulk array bounds check after checking populated elements

Mel Gorman
2021-06-28T11:53:53Z

On Mon, Jun 28, 2021 at 12:27:59AM -0400, Dave Jones wrote:
> On Fri, Jun 18, 2021 at 01:51:02PM +0100, Mel Gorman wrote:
> > Dan Carpenter reported the following
> >
> > The patch 0f87d9d30f21: "mm/page_alloc: add an array-based interface
> > to the bulk page allocator" from Apr 29, 2021, leads to the following
> > static checker warning:
> >
> > mm/page_alloc.c:5338 __alloc_pages_bulk()
> > warn: potentially one past the end of array 'page_array[nr_populated]'
> >
> > The problem can occur if an array is passed in that is fully populated. That
> > potentially ends up allocating a single page and storing it past the end of
> > the array. This patch returns 0 if the array is fully populated.
> >
> > Fixes: 0f87d9d30f21 ("mm/page_alloc: add an array-based interface to the bulk page allocator")
> > Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
> > Signed-off-by: Mel Gorman <mgorman@techsinguliarity.net>
> > ---
> > mm/page_alloc.c | 4 ++++
> > 1 file changed, 4 insertions(+)
> >
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 7124bb00219d..ef2265f86b91 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -5056,6 +5056,10 @@ unsigned long __alloc_pages_bulk(gfp_t gfp, int preferred_nid,
> > while (page_array && nr_populated < nr_pages && page_array[nr_populated])
> > nr_populated++;
> >
> > + /* Already populated array? */
> > + if (unlikely(page_array && nr_pages - nr_populated == 0))
> > + return 0;
> > +
> > /* Use the single page allocator for one page. */
> > if (nr_pages - nr_populated == 1)
> > goto failed;
>
>
> This made it into 5.13 final, and completely breaks NFSD for me (Serving tcp v3 mounts).
> Existing mounts on clients hang, as do new mounts from new clients.
> Rebooting the server back to rc7 everything recovers. Bisect lands on
> this commit.
>

Thanks Dave, can you try this?

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index ef2265f86b91..04220581579c 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5058,7 +5058,7 @@ unsigned long __alloc_pages_bulk(gfp_t gfp, int preferred_nid,

/* Already populated array? */
if (unlikely(page_array && nr_pages - nr_populated == 0))
- return 0;
+ return nr_populated;

/* Use the single page allocator for one page. */
if (nr_pages - nr_populated == 1)