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Commit 18a2f371 authored by Mel Gorman's avatar Mel Gorman Committed by Linus Torvalds
Browse files

tmpfs: fix shared mempolicy leak 



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

Commit 00442ad0 ("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 00442ad0,
alloc_pages_vma() has kept refcount in balance, so now no problem.

Reported-and-tested-by: default avatarTommi Rantala <tt.rantala@gmail.com>
Signed-off-by: default avatarMel Gorman <mgorman@suse.de>
Signed-off-by: default avatarHugh Dickins <hughd@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent c702418f

include/linux/mempolicy.h

+0 −16
Original line number Diff line number Diff line
@@ -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)

{

}

mm/mempolicy.c

+0 −22
Original line number Diff line number Diff line
@@ -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)

{

mm/shmem.c

+16 −10
Original line number Diff line number Diff line
@@ -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