mm: stop leaking PageTables

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@linux.vnet.ibm.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Michael Neuling <mikey@neuling.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/mm/memory.c b/mm/memory.c
index 35d8217..47248dc 100644 (file)
--- 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,