From 05f144a0d5c2207a0349348127f996e104ad7404 Mon Sep 17 00:00:00 2001 From: Mel Gorman Date: Wed, 23 May 2012 12:48:13 +0100 Subject: [PATCH] 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 Cc: Dave Jones Cc: KOSAKI Motohiro Cc: Stephen Wilson Cc: Christoph Lameter Cc: Andrew Morton Cc: Signed-off-by: Linus Torvalds --- mm/mempolicy.c | 41 +++++++++++++++++------------------------ 1 file changed, 17 insertions(+), 24 deletions(-) diff --git a/mm/mempolicy.c b/mm/mempolicy.c index 39fd416ae14f..88f9422b92e7 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: -- 2.20.1