tmpfs: fix shared mempolicy leak

This fixes a regression in 3.7-rc, which has since gone into stable.

Commit 00442ad04a5e ("mempolicy: fix a memory corruption by refcount
imbalance in alloc_pages_vma()") changed get_vma_policy() to raise the
refcount on a shmem shared mempolicy; whereas shmem_alloc_page() went
on expecting alloc_page_vma() to drop the refcount it had acquired.
This deserves a rework: but for now fix the leak in shmem_alloc_page().

Hugh: shmem_swapin() did not need a fix, but surely it's clearer to use
the same refcounting there as in shmem_alloc_page(), delete its onstack
mempolicy, and the strange mpol_cond_copy() and __mpol_cond_copy() -
those were invented to let swapin_readahead() make an unknown number of
calls to alloc_pages_vma() with one mempolicy; but since 00442ad04a5e,
alloc_pages_vma() has kept refcount in balance, so now no problem.

Reported-and-tested-by: Tommi Rantala <tt.rantala@gmail.com>
Signed-off-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 0 insertions, 16 deletions

diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h
index e5ccb9ddd90e..dbd212723b74 100644
--- a/include/linux/mempolicy.h
+++ b/include/linux/mempolicy.h
@@ -82,16 +82,6 @@ static inline void mpol_cond_put(struct mempolicy *pol)
                 __mpol_put(pol);
 }
 
-extern struct mempolicy *__mpol_cond_copy(struct mempolicy *tompol,
-                                          struct mempolicy *frompol);
-static inline struct mempolicy *mpol_cond_copy(struct mempolicy *tompol,
-                                                struct mempolicy *frompol)
-{
-        if (!frompol)
-                return frompol;
-        return __mpol_cond_copy(tompol, frompol);
-}
-
 extern struct mempolicy *__mpol_dup(struct mempolicy *pol);
 static inline struct mempolicy *mpol_dup(struct mempolicy *pol)
 {
@@ -215,12 +205,6 @@ static inline void mpol_cond_put(struct mempolicy *pol)
 {
 }
 
-static inline struct mempolicy *mpol_cond_copy(struct mempolicy *to,
-                                                struct mempolicy *from)
-{
-        return from;
-}
-
 static inline void mpol_get(struct mempolicy *pol)
 {
 }