Fix a lock reversal problem in the VM subsystem related to threaded

programs.   There is a case during a fork() which can cause a deadlock.

From Tor -
The workaround that consists of setting a flag in the vm map that
indicates that a fork is in progress and using that mark in the page
fault handling to force a revalidation failure.  That change will only
affect (pessimize) page fault handling during fork for threaded
(linuxthreads style) applications and applications using aio_*().

Submited by: tegge

1 files changed, 3 insertions, 0 deletions

diff --git a/sys/vm/vm_map.c b/sys/vm/vm_map.c
index 2b57b9da404b..6ff0ab9fa74e 100644
--- a/sys/vm/vm_map.c
+++ b/sys/vm/vm_map.c
@@ -254,6 +254,7 @@ vm_map_init(map, min, max)
 	map->nentries = 0;
 	map->size = 0;
 	map->system_map = 0;
+	map->infork = 0;
 	map->min_offset = min;
 	map->max_offset = max;
 	map->first_free = &map->header;
@@ -2123,6 +2124,7 @@ vmspace_fork(vm1)
 	vm_object_t object;
 
 	vm_map_lock(old_map);
+	old_map->infork = 1;
 
 	vm2 = vmspace_alloc(old_map->min_offset, old_map->max_offset);
 	bcopy(&vm1->vm_startcopy, &vm2->vm_startcopy,
@@ -2215,6 +2217,7 @@ vmspace_fork(vm1)
 	}
 
 	new_map->size = old_map->size;
+	old_map->infork = 0;
 	vm_map_unlock(old_map);
 
 	return (vm2);