mm: numa: add paranoid check around pte_protnone_numa

Mel Gorman · torvalds · commit c0e7cad9f239 · 2015-02-12T18:54:08.000-08:00
pte_protnone_numa is only safe to use after VMA checks for PROT_NONE are
complete.  Treating a real PROT_NONE PTE as a NUMA hinting fault is going
to result in strangeness so add a check for it.  BUG_ON looks like
overkill but if this is hit then it's a serious bug that could result in
corruption so do not even try recovering.  It would have been more
comprehensive to check VMA flags in pte_protnone_numa but it would have
made the API ugly just for a debugging check.

Signed-off-by: Mel Gorman &lt;mgorman@suse.de&gt;
Cc: Aneesh Kumar K.V &lt;aneesh.kumar@linux.vnet.ibm.com&gt;
Cc: Benjamin Herrenschmidt &lt;benh@kernel.crashing.org&gt;
Cc: Dave Jones &lt;davej@redhat.com&gt;
Cc: Hugh Dickins &lt;hughd@google.com&gt;
Cc: Ingo Molnar &lt;mingo@redhat.com&gt;
Cc: Kirill Shutemov &lt;kirill.shutemov@linux.intel.com&gt;
Cc: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
Cc: Paul Mackerras &lt;paulus@samba.org&gt;
Cc: Rik van Riel &lt;riel@redhat.com&gt;
Cc: Sasha Levin &lt;sasha.levin@oracle.com&gt;
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
@@ -1262,6 +1262,9 @@ int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
 	bool migrated = false;
 	int flags = 0;
 
+	/* A PROT_NONE fault should not end up here */
+	BUG_ON(!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)));
+
 	ptl = pmd_lock(mm, pmdp);
 	if (unlikely(!pmd_same(pmd, *pmdp)))
 		goto out_unlock;
diff --git a/mm/memory.c b/mm/memory.c
@@ -3013,6 +3013,9 @@ static int do_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
 	bool migrated = false;
 	int flags = 0;
 
+	/* A PROT_NONE fault should not end up here */
+	BUG_ON(!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)));
+
 	/*
 	* The "pte" at this point cannot be used safely without
 	* validation through pte_unmap_same(). It's of NUMA type but
