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-rw-r--r--include/linux/rmap.h8
1 files changed, 8 insertions, 0 deletions
diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 1383692ac5b..69407f85e10 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -26,6 +26,14 @@
*/
struct anon_vma {
spinlock_t lock; /* Serialize access to vma list */
+ /*
+ * NOTE: the LSB of the head.next is set by
+ * mm_take_all_locks() _after_ taking the above lock. So the
+ * head must only be read/written after taking the above lock
+ * to be sure to see a valid next pointer. The LSB bit itself
+ * is serialized by a system wide lock only visible to
+ * mm_take_all_locks() (mm_all_locks_mutex).
+ */
struct list_head head; /* List of private "related" vmas */
};