[PATCH 4.9 58/58] mm: stop leaking PageTables

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Hugh Dickins <hughd@xxxxxxxxxx>

commit b0b9b3df27d100a975b4e8818f35382b64a5e35c upstream.

4.10-rc loadtest (even on x86, and even without THPCache) fails with
"fork: Cannot allocate memory" or some such; and /proc/meminfo shows
PageTables growing.

Commit 953c66c2b22a ("mm: THP page cache support for ppc64") that got
merged in rc1 removed the freeing of an unused preallocated pagetable
after do_fault_around() has called map_pages().

This is usually a good optimization, so that the followup doesn't have
to reallocate one; but it's not sufficient to shift the freeing into
alloc_set_pte(), since there are failure cases (most commonly
VM_FAULT_RETRY) which never reach finish_fault().

Check and free it at the outer level in do_fault(), then we don't need
to worry in alloc_set_pte(), and can restore that to how it was (I
cannot find any reason to pte_free() under lock as it was doing).

And fix a separate pagetable leak, or crash, introduced by the same
change, that could only show up on some ppc64: why does do_set_pmd()'s
failure case attempt to withdraw a pagetable when it never deposited
one, at the same time overwriting (so leaking) the vmf->prealloc_pte?
Residue of an earlier implementation, perhaps? Delete it.

Fixes: 953c66c2b22a ("mm: THP page cache support for ppc64")
Cc: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Michael Neuling <mikey@xxxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Balbir Singh <bsingharora@xxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 mm/memory.c |   21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3329,15 +3329,24 @@ static int do_fault(struct fault_env *fe
 {
 	struct vm_area_struct *vma = fe->vma;
 	pgoff_t pgoff = linear_page_index(vma, fe->address);
+	int ret;
 
 	/* The VMA was not fully populated on mmap() or missing VM_DONTEXPAND */
 	if (!vma->vm_ops->fault)
-		return VM_FAULT_SIGBUS;
-	if (!(fe->flags & FAULT_FLAG_WRITE))
-		return do_read_fault(fe, pgoff);
-	if (!(vma->vm_flags & VM_SHARED))
-		return do_cow_fault(fe, pgoff);
-	return do_shared_fault(fe, pgoff);
+		ret = VM_FAULT_SIGBUS;
+	else if (!(fe->flags & FAULT_FLAG_WRITE))
+		ret = do_read_fault(fe, pgoff);
+	else if (!(vma->vm_flags & VM_SHARED))
+		ret = do_cow_fault(fe, pgoff);
+	else
+		ret = do_shared_fault(fe, pgoff);
+
+	/* preallocated pagetable is unused: free it */
+	if (fe->prealloc_pte) {
+		pte_free(vma->vm_mm, fe->prealloc_pte);
+		fe->prealloc_pte = 0;
+	}
+	return ret;
 }
 
 static int numa_migrate_prep(struct page *page, struct vm_area_struct *vma,