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authorMel Gorman <mgorman@suse.de>2012-05-23 12:48:13 +0100
committerLinus Torvalds <torvalds@linux-foundation.org>2012-05-23 17:57:33 -0700
commit05f144a0d5c2207a0349348127f996e104ad7404 (patch)
tree2996c5689ed520557f381cf364739eee2f2b87a4 /mm/mempolicy.c
parent644473e9c60c1ff4f6351fed637a6e5551e3dce7 (diff)
downloadlinux-05f144a0d5c2207a0349348127f996e104ad7404.tar.gz
mm: mempolicy: Let vma_merge and vma_split handle vma->vm_policy linkages
Dave Jones' system call fuzz testing tool "trinity" triggered the following bug error with slab debugging enabled ============================================================================= BUG numa_policy (Not tainted): Poison overwritten ----------------------------------------------------------------------------- INFO: 0xffff880146498250-0xffff880146498250. First byte 0x6a instead of 0x6b INFO: Allocated in mpol_new+0xa3/0x140 age=46310 cpu=6 pid=32154 __slab_alloc+0x3d3/0x445 kmem_cache_alloc+0x29d/0x2b0 mpol_new+0xa3/0x140 sys_mbind+0x142/0x620 system_call_fastpath+0x16/0x1b INFO: Freed in __mpol_put+0x27/0x30 age=46268 cpu=6 pid=32154 __slab_free+0x2e/0x1de kmem_cache_free+0x25a/0x260 __mpol_put+0x27/0x30 remove_vma+0x68/0x90 exit_mmap+0x118/0x140 mmput+0x73/0x110 exit_mm+0x108/0x130 do_exit+0x162/0xb90 do_group_exit+0x4f/0xc0 sys_exit_group+0x17/0x20 system_call_fastpath+0x16/0x1b INFO: Slab 0xffffea0005192600 objects=27 used=27 fp=0x (null) flags=0x20000000004080 INFO: Object 0xffff880146498250 @offset=592 fp=0xffff88014649b9d0 This implied a reference counting bug and the problem happened during mbind(). mbind() applies a new memory policy to a range and uses mbind_range() to merge existing VMAs or split them as necessary. In the event of splits, mpol_dup() will allocate a new struct mempolicy and maintain existing reference counts whose rules are documented in Documentation/vm/numa_memory_policy.txt . The problem occurs with shared memory policies. The vm_op->set_policy increments the reference count if necessary and split_vma() and vma_merge() have already handled the existing reference counts. However, policy_vma() screws it up by replacing an existing vma->vm_policy with one that potentially has the wrong reference count leading to a premature free. This patch removes the damage caused by policy_vma(). With this patch applied Dave's trinity tool runs an mbind test for 5 minutes without error. /proc/slabinfo reported that there are no numa_policy or shared_policy_node objects allocated after the test completed and the shared memory region was deleted. Signed-off-by: Mel Gorman <mgorman@suse.de> Cc: Dave Jones <davej@redhat.com> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Stephen Wilson <wilsons@start.ca> Cc: Christoph Lameter <cl@linux.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: <stable@vger.kernel.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/mempolicy.c')
-rw-r--r--mm/mempolicy.c41
1 files changed, 17 insertions, 24 deletions
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 39fd416ae14..88f9422b92e 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -607,27 +607,6 @@ check_range(struct mm_struct *mm, unsigned long start, unsigned long end,
return first;
}
-/* Apply policy to a single VMA */
-static int policy_vma(struct vm_area_struct *vma, struct mempolicy *new)
-{
- int err = 0;
- struct mempolicy *old = vma->vm_policy;
-
- pr_debug("vma %lx-%lx/%lx vm_ops %p vm_file %p set_policy %p\n",
- vma->vm_start, vma->vm_end, vma->vm_pgoff,
- vma->vm_ops, vma->vm_file,
- vma->vm_ops ? vma->vm_ops->set_policy : NULL);
-
- if (vma->vm_ops && vma->vm_ops->set_policy)
- err = vma->vm_ops->set_policy(vma, new);
- if (!err) {
- mpol_get(new);
- vma->vm_policy = new;
- mpol_put(old);
- }
- return err;
-}
-
/* Step 2: apply policy to a range and do splits. */
static int mbind_range(struct mm_struct *mm, unsigned long start,
unsigned long end, struct mempolicy *new_pol)
@@ -676,9 +655,23 @@ static int mbind_range(struct mm_struct *mm, unsigned long start,
if (err)
goto out;
}
- err = policy_vma(vma, new_pol);
- if (err)
- goto out;
+
+ /*
+ * Apply policy to a single VMA. The reference counting of
+ * policy for vma_policy linkages has already been handled by
+ * vma_merge and split_vma as necessary. If this is a shared
+ * policy then ->set_policy will increment the reference count
+ * for an sp node.
+ */
+ pr_debug("vma %lx-%lx/%lx vm_ops %p vm_file %p set_policy %p\n",
+ vma->vm_start, vma->vm_end, vma->vm_pgoff,
+ vma->vm_ops, vma->vm_file,
+ vma->vm_ops ? vma->vm_ops->set_policy : NULL);
+ if (vma->vm_ops && vma->vm_ops->set_policy) {
+ err = vma->vm_ops->set_policy(vma, new_pol);
+ if (err)
+ goto out;
+ }
}
out: