hugetlb, mbind: fall back to default policy if vma is NULL

Dan Carpenter has noticed that mbind migration callback (new_page) can
get a NULL vma pointer and choke on it inside alloc_huge_page_vma which
relies on the VMA to get the hstate.  We used to BUG_ON this case but
the BUG_+ON has been removed recently by "hugetlb, mempolicy: fix the
mbind hugetlb migration".

The proper way to handle this is to get the hstate from the migrated
page and rely on huge_node (resp.  get_vma_policy) do the right thing
with null VMA.  We are currently falling back to the default mempolicy
in that case which is in line what THP path is doing here.

Link: http://lkml.kernel.org/r/20180110104712.GR1732@dhcp22.suse.cz
Signed-off-by: Michal Hocko <mhocko@suse.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 612a29b..36fa6a2 100644 (file)
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -358,7 +358,8 @@ struct page *alloc_huge_page(struct vm_area_struct *vma,
 struct page *alloc_huge_page_node(struct hstate *h, int nid);
 struct page *alloc_huge_page_nodemask(struct hstate *h, int preferred_nid,
                                nodemask_t *nmask);
-struct page *alloc_huge_page_vma(struct vm_area_struct *vma, unsigned long address);
+struct page *alloc_huge_page_vma(struct hstate *h, struct vm_area_struct *vma,
+                               unsigned long address);
 int huge_add_to_page_cache(struct page *page, struct address_space *mapping,
                        pgoff_t idx);
 
@@ -536,7 +537,7 @@ struct hstate {};
 #define alloc_huge_page(v, a, r) NULL
 #define alloc_huge_page_node(h, nid) NULL
 #define alloc_huge_page_nodemask(h, preferred_nid, nmask) NULL
-#define alloc_huge_page_vma(vma, address) NULL
+#define alloc_huge_page_vma(h, vma, address) NULL
 #define alloc_bootmem_huge_page(h) NULL
 #define hstate_file(f) NULL
 #define hstate_sizelog(s) NULL

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 742a929..7c204e3 100644 (file)
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1675,16 +1675,15 @@ struct page *alloc_huge_page_nodemask(struct hstate *h, int preferred_nid,
 }
 
 /* mempolicy aware migration callback */
-struct page *alloc_huge_page_vma(struct vm_area_struct *vma, unsigned long address)
+struct page *alloc_huge_page_vma(struct hstate *h, struct vm_area_struct *vma,
+               unsigned long address)
 {
        struct mempolicy *mpol;
        nodemask_t *nodemask;
        struct page *page;
-       struct hstate *h;
        gfp_t gfp_mask;
        int node;
 
-       h = hstate_vma(vma);
        gfp_mask = htlb_alloc_mask(h);
        node = huge_node(vma, address, gfp_mask, &mpol, &nodemask);
        page = alloc_huge_page_nodemask(h, node, nodemask);

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 96823fa..d879f1d 100644 (file)
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1121,7 +1121,8 @@ static struct page *new_page(struct page *page, unsigned long start, int **x)
        }
 
        if (PageHuge(page)) {
-               return alloc_huge_page_vma(vma, address);
+               return alloc_huge_page_vma(page_hstate(compound_head(page)),
+                               vma, address);
        } else if (thp_migration_supported() && PageTransHuge(page)) {
                struct page *thp;