tmpfs: fix shared mempolicy leak

Mel Gorman · torvalds · commit 18a2f371f5ed · 2012-12-06T11:56:43.000-08:00
This fixes a regression in 3.7-rc, which has since gone into stable. Commit 00442ad ("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 00442ad, 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>
diff --git 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)
 {
 }
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
@@ -2037,28 +2037,6 @@ 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
@@ -910,25 +910,29 @@ 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;
 	/* Bias interleave by inode number to distribute better across nodes */
 	pvma.vm_pgoff = index + info->vfs_inode.i_ino;
 	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;
@@ -937,10 +941,12 @@ 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

Original file line number	Diff line number	Diff line change
`@@ -82,16 +82,6 @@ static inline void mpol_cond_put(struct mempolicy *pol)`
`82`	`82`	`__mpol_put(pol);`
`83`	`83`	`}`
`84`	`84`
`85`		`-extern struct mempolicy __mpol_cond_copy(struct mempolicy tompol,`
`86`		`- struct mempolicy *frompol);`
`87`		`-static inline struct mempolicy mpol_cond_copy(struct mempolicy tompol,`
`88`		`- struct mempolicy *frompol)`
`89`		`-{`
`90`		`- if (!frompol)`
`91`		`- return frompol;`
`92`		`- return __mpol_cond_copy(tompol, frompol);`
`93`		`-}`
`94`		`-`
`95`	`85`	`extern struct mempolicy __mpol_dup(struct mempolicy pol);`
`96`	`86`	`static inline struct mempolicy mpol_dup(struct mempolicy pol)`
`97`	`87`	`{`
`@@ -215,12 +205,6 @@ static inline void mpol_cond_put(struct mempolicy *pol)`
`215`	`205`	`{`
`216`	`206`	`}`
`217`	`207`
`218`		`-static inline struct mempolicy mpol_cond_copy(struct mempolicy to,`
`219`		`- struct mempolicy *from)`
`220`		`-{`
`221`		`- return from;`
`222`		`-}`
`223`		`-`
`224`	`208`	`static inline void mpol_get(struct mempolicy *pol)`
`225`	`209`	`{`
`226`	`210`	`}`