Add a comment documenting a race condition in vm_fault(): Specifically, a

modification is made to the vm_map while only a read lock is held.

1 files changed, 3 insertions, 0 deletions

diff --git a/sys/vm/vm_fault.c b/sys/vm/vm_fault.c
index 2d463500554b..bdac6b840dd7 100644
--- a/sys/vm/vm_fault.c
+++ b/sys/vm/vm_fault.c
@@ -258,6 +258,9 @@ RetryFault:;
 		 * If we don't COW now, on a user wire, the user will never
 		 * be able to write to the mapping.  If we don't make this
 		 * restriction, the bookkeeping would be nearly impossible.
+		 *
+		 * XXX The following assignment modifies the map without
+		 * holding a write lock on it.
 		 */
 		if ((fs.entry->protection & VM_PROT_WRITE) == 0)
 			fs.entry->max_protection &= ~VM_PROT_WRITE;