Re: [PATCH v3 1/4] hugetlb: Fix wrong use of nr_online_nodes

[Kefeng Wang]

On 2022/4/15 13:41, Kefeng Wang wrote:
> On 2022/4/15 10:09, Davidlohr Bueso wrote:
> > On Wed, 13 Apr 2022, Peng Liu wrote:
> >
> > > Certain systems are designed to have sparse/discontiguous nodes. In
> > > this case, nr_online_nodes can not be used to walk through numa node.
> > > Also, a valid node may be greater than nr_online_nodes.
> > >
> > > However, in hugetlb, it is assumed that nodes are contiguous. Recheck
> > > all the places that use nr_online_nodes, and repair them one by one.
> > >
> > > Suggested-by: David Hildenbrand <david@xxxxxxxxxx>
> > > Fixes: 4178158ef8ca ("hugetlbfs: fix issue of preallocation of 
> > > gigantic pages can't work")
> > > Fixes: b5389086ad7b ("hugetlbfs: extend the definition of hugepages 
> > > parameter to support node allocation")
> > > Fixes: e79ce9832316 ("hugetlbfs: fix a truncation issue in hugepages 
> > > parameter")
> > > Fixes: f9317f77a6e0 ("hugetlb: clean up potential spectre issue 
> > > warnings")
> > > Signed-off-by: Peng Liu <liupeng256@xxxxxxxxxx>
> > > Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> > > Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> >
> > Reviewed-by: Davidlohr Bueso <dave@xxxxxxxxxxxx>
> >
> > ... but
> >
> > > ---
> > > mm/hugetlb.c | 12 ++++++------
> > > 1 file changed, 6 insertions(+), 6 deletions(-)
> > >
> > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> > > index b34f50156f7e..5b5a2a5a742f 100644
> > > --- a/mm/hugetlb.c
> > > +++ b/mm/hugetlb.c
> > > @@ -2979,7 +2979,7 @@ int __alloc_bootmem_huge_page(struct hstate 
> > > *h, int nid)
> > >     struct huge_bootmem_page *m = NULL; /* initialize for clang */
> > >     int nr_nodes, node;
> > >
> > > -    if (nid != NUMA_NO_NODE && nid >= nr_online_nodes)
> > > +    if (nid != NUMA_NO_NODE && !node_online(nid))
> >
> > afaict null_blk could also use this, actually the whole thing wants a
> > helper - node_valid()?
> This one should be unnecessary, and this patch looks has a bug,
>
> if a very nid passed to node_online(), it may crash,  could you 
> re-check it,
>
> see my changes below,
>
> 1) add tmp check against MAX_NUMNODES before node_online() check,
>
>     and move it after get tmp in hugepages_setup() , this could cover 
> both per-node alloc and normal alloc

sorry，for normal alloc, tmp is the number of huge pages, we don't  need 
the movement,   only add tmp >= MAX_NUMNODES is ok

> 2) due to for_each_online_node() usage, we can drop additional check 
> of nid in __alloc_bootmem_huge_page()