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

Dave Jones
2021-06-28T04:59:45Z

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.

replacing the return 0 with a warn gets me this:

[ 15.127686] WARNING: CPU: 1 PID: 1673 at mm/page_alloc.c:5060 __alloc_pages_bulk+0x6a/0x560
[ 15.129286] CPU: 1 PID: 1673 Comm: lockd Not tainted 5.13.0-firewall+ #15
[ 15.129290] Hardware name: To be filled by O.E.M. To be filled by O.E.M./Q3XXG4-P, BIOS 5.6.5 06/30/2018
[ 15.129292] RIP: 0010:__alloc_pages_bulk+0x6a/0x560
[ 15.129301] Code: 00 48 83 38 00 0f 84 69 04 00 00 48 83 c0 08 31 db eb 0f 48 83 c0 08 48 83 78 f8 00 0f 84 72 03 00 00 83 c3 01 41 39 df 75 e9 <0f> 0b 8b 05 0e 71 32 01 8b 6c 24 14 23 2d 10 71 32 01 85 c0 0f 85
[ 15.129303] RSP: 0018:ffffb920031e7e10 EFLAGS: 00010246
[ 15.129306] RAX: ffff9fff4ef502f0 RBX: 0000000000000004 RCX: 0000000000000004
[ 15.129308] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000cc0
[ 15.129309] RBP: 0000000000000004 R08: 0000000000000000 R09: ffff9fff4ef502d0
[ 15.129311] R10: 0000000000000000 R11: 0000000000000002 R12: ffff9fff42186240
[ 15.129312] R13: 7fffffffffffffff R14: 0000000000000004 R15: 0000000000000004
[ 15.129317] FS: 0000000000000000(0000) GS:ffffa00057480000(0000) knlGS:0000000000000000
[ 15.129319] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 15.129321] CR2: 00007f0bf731c000 CR3: 000000007840b002 CR4: 00000000001706e0
[ 15.129323] Call Trace:
[ 15.129327] svc_recv+0x7a/0x820
[ 15.129333] ? __schedule+0x358/0x700
[ 15.129338] ? nlmsvc_retry_blocked+0x1b/0x280
[ 15.156135] ? grace_ender+0x20/0x20
[ 15.157546] lockd+0x83/0x140
[ 15.157564] kthread+0x116/0x140
[ 15.157569] ? __kthread_create_on_node+0x180/0x180
[ 15.157574] ret_from_fork+0x22/0x30
[ 15.157579] ---[ end trace 0854dec2f1b25912 ]---