path: root/ipc
diff options
authorLee Schermerhorn <Lee.Schermerhorn@hp.com>2008-03-10 11:43:45 -0700
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2008-03-10 18:01:19 -0700
commit69682d852f5c94ee94e21174b3e8b719626c98db (patch)
treeed3c7c0681ef7658132ae32f1cd8a56bb6451621 /ipc
parent9afa802ff568d935dab33dd207dc25d9849f35d4 (diff)
mempolicy: fix reference counting bugs
Address 3 known bugs in the current memory policy reference counting method. I have a series of patches to rework the reference counting to reduce overhead in the allocation path. However, that series will require testing in -mm once I repost it. 1) alloc_page_vma() does not release the extra reference taken for vma/shared mempolicy when the mode == MPOL_INTERLEAVE. This can result in leaking mempolicy structures. This is probably occurring, but not being noticed. Fix: add the conditional release of the reference. 2) hugezonelist unconditionally releases a reference on the mempolicy when mode == MPOL_INTERLEAVE. This can result in decrementing the reference count for system default policy [should have no ill effect] or premature freeing of task policy. If this occurred, the next allocation using task mempolicy would use the freed structure and probably BUG out. Fix: add the necessary check to the release. 3) The current reference counting method assumes that vma 'get_policy()' methods automatically add an extra reference a non-NULL returned mempolicy. This is true for shmem_get_policy() used by tmpfs mappings, including regular page shm segments. However, SHM_HUGETLB shm's, backed by hugetlbfs, just use the vma policy without the extra reference. This results in freeing of the vma policy on the first allocation, with reuse of the freed mempolicy structure on subsequent allocations. Fix: Rather than add another condition to the conditional reference release, which occur in the allocation path, just add a reference when returning the vma policy in shm_get_policy() to match the assumptions. Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com> Cc: Greg KH <greg@kroah.com> Cc: Andi Kleen <ak@suse.de> Cc: Christoph Lameter <clameter@sgi.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: David Rientjes <rientjes@google.com> Cc: <eric.whitney@hp.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'ipc')
1 files changed, 3 insertions, 2 deletions
diff --git a/ipc/shm.c b/ipc/shm.c
index c47e87278a9..cc63fae02f0 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -271,9 +271,10 @@ static struct mempolicy *shm_get_policy(struct vm_area_struct *vma,
if (sfd->vm_ops->get_policy)
pol = sfd->vm_ops->get_policy(vma, addr);
- else if (vma->vm_policy)
+ else if (vma->vm_policy) {
pol = vma->vm_policy;
- else
+ mpol_get(pol); /* get_vma_policy() expects this */
+ } else
pol = current->mempolicy;
return pol;