Messages in this thread Patch in this message | | | From | Peter Xu <> | Subject | [PATCH] mm/gup: Fix follow_devmap_p[mu]d() on page==NULL handling | Date | Thu, 23 Nov 2023 13:02:22 -0500 |
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This is a bug found not by any report but only by code observations.
When GUP sees a devpmd/devpud and if page==NULL is returned, it means a fault is probably required. Here falling through when page==NULL can cause unexpected behavior.
Fix both cases by catching the page==NULL cases with no_page_table().
Fixes: 3565fce3a659 ("mm, x86: get_user_pages() for dax mappings") Fixes: 080dbb618b4b ("mm/follow_page_mask: split follow_page_mask to smaller functions.") Cc: Dan Williams <dan.j.williams@intel.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Matthew Wilcox <willy@infradead.org> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com> Cc: Christoph Hellwig <hch@lst.de> Signed-off-by: Peter Xu <peterx@redhat.com> --- mm/gup.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/mm/gup.c b/mm/gup.c index 231711efa390..0a5f0e91bfec 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -710,6 +710,7 @@ static struct page *follow_pmd_mask(struct vm_area_struct *vma, spin_unlock(ptl); if (page) return page; + return no_page_table(vma, flags); } if (likely(!pmd_trans_huge(pmdval))) return follow_page_pte(vma, address, pmd, flags, &ctx->pgmap); @@ -758,6 +759,7 @@ static struct page *follow_pud_mask(struct vm_area_struct *vma, spin_unlock(ptl); if (page) return page; + return no_page_table(vma, flags); } if (unlikely(pud_bad(*pud))) return no_page_table(vma, flags); -- 2.41.0
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