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Diffstat (limited to 'mm/rmap.c')
-rw-r--r--mm/rmap.c18
1 files changed, 16 insertions, 2 deletions
diff --git a/mm/rmap.c b/mm/rmap.c
index b65f00d1707f..caa48b27371b 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -132,6 +132,11 @@ int anon_vma_prepare(struct vm_area_struct *vma)
if (unlikely(!anon_vma))
goto out_enomem_free_avc;
allocated = anon_vma;
+ /*
+ * This VMA had no anon_vma yet. This anon_vma is
+ * the root of any anon_vma tree that might form.
+ */
+ anon_vma->root = anon_vma;
}
anon_vma_lock(anon_vma);
@@ -224,9 +229,15 @@ int anon_vma_fork(struct vm_area_struct *vma, struct vm_area_struct *pvma)
avc = anon_vma_chain_alloc();
if (!avc)
goto out_error_free_anon_vma;
- anon_vma_chain_link(vma, avc, anon_vma);
+
+ /*
+ * The root anon_vma's spinlock is the lock actually used when we
+ * lock any of the anon_vmas in this anon_vma tree.
+ */
+ anon_vma->root = pvma->anon_vma->root;
/* Mark this anon_vma as the one where our new (COWed) pages go. */
vma->anon_vma = anon_vma;
+ anon_vma_chain_link(vma, avc, anon_vma);
return 0;
@@ -261,7 +272,10 @@ void unlink_anon_vmas(struct vm_area_struct *vma)
{
struct anon_vma_chain *avc, *next;
- /* Unlink each anon_vma chained to the VMA. */
+ /*
+ * Unlink each anon_vma chained to the VMA. This list is ordered
+ * from newest to oldest, ensuring the root anon_vma gets freed last.
+ */
list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) {
anon_vma_unlink(avc);
list_del(&avc->same_vma);