Change Details

Otherwise we are susceptible to a race with a concurrent vm_map_wire() call, which faults pages into the object chain and drops the map lock between each call to vm_fault(). In particular, vm_map_protect() will only copy newly writable wired pages if MAP_ENTRY_USER_WIRED is set, but vm_map_wire() only sets this flag after the fault loop. So we may end up with a PROT_WRITE wired map entry whose top-level object does not contain the entire range of pages. It is also possible to address this race by checking for in-transition map entries in the final loop of vm_map_protect(), but that is more complicated and requires some restart logic, and I don't see any real benefits. Unrelated changes are to add assertions to the map clip functions (resulting from a bug in my first attempt to check for and handle MAP_ENTRY_IN_TRANSITION entries in vm_map_protect()), and to consistently use for-loops in vm_map_protect().

Otherwise we are susceptible to a race with a concurrent vm_map_wire() call, which faults pages into the object chain and drops the map lock between each call to vm_fault(). In particular, vm_map_protect() will only copy newly writable wired pages if MAP_ENTRY_USER_WIRED is set, but vm_map_wire() only sets this flag after the fault loop. So we may end up with a PROT_WRITE wired map entry whose top-level object does not contain the entire range of pages. It is also possible to address this race by checking for in-transition map entries in the final loop of vm_map_protect(), but that is more complicated since it requires some restart logic, and I don't see any real benefits. Unrelated changes are to add assertions to the map clip functions (motivated by a bug in my first attempt to check for and handle MAP_ENTRY_IN_TRANSITION entries in vm_map_protect()), and to consistently use for-loops in vm_map_protect().

Otherwise we are susceptible to a race with a concurrent vm_map_wire() call, which faults pages into the object chain and drops the map lock between each call to vm_fault(). In particular, vm_map_protect() will only copy newly writable wired pages if MAP_ENTRY_USER_WIRED is set, but vm_map_wire() only sets this flag after the fault loop. So we may end up with a PROT_WRITE wired map entry whose top-level object does not contain the entire range of pages. It is also possible to address this race by checking for in-transition map entries in the final loop of vm_map_protect(), but that is more complicated andsince it requires some restart logic, and I don't see any real real benefits. Unrelated changes are to add assertions to the map clip functions (resulting frommotivated by a bug in my first attempt to check for and handle MAP_ENTRY_IN_TRANSITION entries in vm_map_protect()), and to consistently use for-loops in vm_map_protect().