[ 3.5.y.z extended stable ] Patch "tmpfs: fix shared mempolicy leak" has been added to staging queue

[Herton Ronaldo Krzesinski]

This is a note to let you know that I have just added a patch titled

    tmpfs: fix shared mempolicy leak

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Herton

------

>From eb00f335714a5e8c3df3398b2eb5bc61ec251e14 Mon Sep 17 00:00:00 2001
From: Mel Gorman <mgorman at suse.de>
Date: Wed, 5 Dec 2012 14:01:41 -0800
Subject: [PATCH 03/11] tmpfs: fix shared mempolicy leak

commit 18a2f371f5edf41810f6469cb9be39931ef9deb9 upstream.

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 at gmail.com>
Signed-off-by: Mel Gorman <mgorman at suse.de>
Signed-off-by: Hugh Dickins <hughd at google.com>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
[ herton: adjust context ]
Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski at canonical.com>
---
 include/linux/mempolicy.h |   16 ----------------
 mm/mempolicy.c            |   22 ----------------------
 mm/shmem.c                |   26 ++++++++++++++++----------
 3 files changed, 16 insertions(+), 48 deletions(-)

diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h
index c252970..7539a67 100644
--- a/include/linux/mempolicy.h
+++ b/include/linux/mempolicy.h
@@ -137,16 +137,6 @@ 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)
 {
@@ -270,12 +260,6 @@ 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)
 {
 }
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index cee020c..e65ca51 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2029,28 +2029,6 @@ struct mempolicy *__mpol_dup(struct mempolicy *old)
 	return new;
 }

-/*
- * If *frompol needs [has] an extra ref, copy *frompol to *tompol ,
- * eliminate the * MPOL_F_* flags that require conditional ref and
- * [NOTE!!!] drop the extra ref.  Not safe to reference *frompol directly
- * after return.  Use the returned value.
- *
- * Allows use of a mempolicy for, e.g., multiple allocations with a single
- * policy lookup, even if the policy needs/has extra ref on lookup.
- * shmem_readahead needs this.
- */
-struct mempolicy *__mpol_cond_copy(struct mempolicy *tompol,
-						struct mempolicy *frompol)
-{
-	if (!mpol_needs_cond_ref(frompol))
-		return frompol;
-
-	*tompol = *frompol;
-	tompol->flags &= ~MPOL_F_SHARED;	/* copy doesn't need unref */
-	__mpol_put(frompol);
-	return tompol;
-}
-
 /* Slow path of a mempolicy comparison */
 bool __mpol_equal(struct mempolicy *a, struct mempolicy *b)
 {
diff --git a/mm/shmem.c b/mm/shmem.c
index 8d0c102..626a7e7 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -921,24 +921,28 @@ static struct mempolicy *shmem_get_sbmpol(struct shmem_sb_info *sbinfo)
 static struct page *shmem_swapin(swp_entry_t swap, gfp_t gfp,
 			struct shmem_inode_info *info, pgoff_t index)
 {
-	struct mempolicy mpol, *spol;
 	struct vm_area_struct pvma;
-
-	spol = mpol_cond_copy(&mpol,
-			mpol_shared_policy_lookup(&info->policy, index));
+	struct page *page;

 	/* Create a pseudo vma that just contains the policy */
 	pvma.vm_start = 0;
 	pvma.vm_pgoff = index;
 	pvma.vm_ops = NULL;
-	pvma.vm_policy = spol;
-	return swapin_readahead(swap, gfp, &pvma, 0);
+	pvma.vm_policy = mpol_shared_policy_lookup(&info->policy, index);
+
+	page = swapin_readahead(swap, gfp, &pvma, 0);
+
+	/* Drop reference taken by mpol_shared_policy_lookup() */
+	mpol_cond_put(pvma.vm_policy);
+
+	return page;
 }

 static struct page *shmem_alloc_page(gfp_t gfp,
 			struct shmem_inode_info *info, pgoff_t index)
 {
 	struct vm_area_struct pvma;
+	struct page *page;

 	/* Create a pseudo vma that just contains the policy */
 	pvma.vm_start = 0;
@@ -946,10 +950,12 @@ static struct page *shmem_alloc_page(gfp_t gfp,
 	pvma.vm_ops = NULL;
 	pvma.vm_policy = mpol_shared_policy_lookup(&info->policy, index);

-	/*
-	 * alloc_page_vma() will drop the shared policy reference
-	 */
-	return alloc_page_vma(gfp, &pvma, 0);
+	page = alloc_page_vma(gfp, &pvma, 0);
+
+	/* Drop reference taken by mpol_shared_policy_lookup() */
+	mpol_cond_put(pvma.vm_policy);
+
+	return page;
 }
 #else /* !CONFIG_NUMA */
 #ifdef CONFIG_TMPFS
--
1.7.9.5