Author: mlaier
Date: Thu Dec 9 21:02:22 2010
New Revision: 216335
URL: http://svn.freebsd.org/changeset/base/216335
Log:
Fix a long standing (from the original 4.4BSD lite sources) race between
vmspace_fork and vm_map_wire that would lead to "vm_fault_copy_wired: page
missing" panics. While faulting in pages for a map entry that is being
wired down, mark the containing map as busy. In vmspace_fork wait until the
map is unbusy, before we try to copy the entries.
Reviewed by: kib
MFC after: 5 days
Sponsored by: Isilon Systems, Inc.
Modified:
head/sys/vm/vm_map.c
head/sys/vm/vm_map.h
Modified: head/sys/vm/vm_map.c
==============================================================================
--- head/sys/vm/vm_map.c Thu Dec 9 20:28:30 2010 (r216334)
+++ head/sys/vm/vm_map.c Thu Dec 9 21:02:22 2010 (r216335)
@@ -671,6 +671,41 @@ vm_map_wakeup(vm_map_t map)
wakeup(&map->root);
}
+void
+vm_map_busy(vm_map_t map)
+{
+
+ VM_MAP_ASSERT_LOCKED(map);
+ map->busy++;
+}
+
+void
+vm_map_unbusy(vm_map_t map)
+{
+
+ VM_MAP_ASSERT_LOCKED(map);
+ KASSERT(map->busy, ("vm_map_unbusy: not busy"));
+ if (--map->busy == 0 && (map->flags & MAP_BUSY_WAKEUP)) {
+ vm_map_modflags(map, 0, MAP_BUSY_WAKEUP);
+ wakeup(&map->busy);
+ }
+}
+
+void
+vm_map_wait_busy(vm_map_t map)
+{
+
+ VM_MAP_ASSERT_LOCKED(map);
+ while (map->busy) {
+ vm_map_modflags(map, MAP_BUSY_WAKEUP, 0);
+ if (map->system_map)
+ msleep(&map->busy, &map->system_mtx, 0, "mbusy", 0);
+ else
+ sx_sleep(&map->busy, &map->lock, 0, "mbusy", 0);
+ }
+ map->timestamp++;
+}
+
long
vmspace_resident_count(struct vmspace *vmspace)
{
@@ -718,6 +753,7 @@ _vm_map_init(vm_map_t map, pmap_t pmap,
map->flags = 0;
map->root = NULL;
map->timestamp = 0;
+ map->busy = 0;
}
void
@@ -2382,12 +2418,14 @@ vm_map_wire(vm_map_t map, vm_offset_t st
entry->object.vm_object->type == OBJT_SG);
/*
* Release the map lock, relying on the in-transition
- * mark.
+ * mark. Mark the map busy for fork.
*/
+ vm_map_busy(map);
vm_map_unlock(map);
rv = vm_fault_wire(map, saved_start, saved_end,
fictitious);
vm_map_lock(map);
+ vm_map_unbusy(map);
if (last_timestamp + 1 != map->timestamp) {
/*
* Look again for the entry because the map was
@@ -2995,6 +3033,8 @@ vmspace_fork(struct vmspace *vm1, vm_oof
int locked;
vm_map_lock(old_map);
+ if (old_map->busy)
+ vm_map_wait_busy(old_map);
vm2 = vmspace_alloc(old_map->min_offset, old_map->max_offset);
if (vm2 == NULL)
goto unlock_and_return;
Modified: head/sys/vm/vm_map.h
==============================================================================
--- head/sys/vm/vm_map.h Thu Dec 9 20:28:30 2010 (r216334)
+++ head/sys/vm/vm_map.h Thu Dec 9 21:02:22 2010 (r216335)
@@ -187,12 +187,14 @@ struct vm_map {
pmap_t pmap; /* (c) Physical map */
#define min_offset header.start /* (c) */
#define max_offset header.end /* (c) */
+ int busy;
};
/*
* vm_flags_t values
*/
#define MAP_WIREFUTURE 0x01 /* wire all future pages */
+#define MAP_BUSY_WAKEUP 0x02
#ifdef _KERNEL
static __inline vm_offset_t
@@ -275,6 +277,9 @@ int _vm_map_lock_upgrade(vm_map_t map, c
void _vm_map_lock_downgrade(vm_map_t map, const char *file, int line);
int vm_map_locked(vm_map_t map);
void vm_map_wakeup(vm_map_t map);
+void vm_map_busy(vm_map_t map);
+void vm_map_unbusy(vm_map_t map);
+void vm_map_wait_busy(vm_map_t map);
#define vm_map_lock(map) _vm_map_lock(map, LOCK_FILE, LOCK_LINE)
#define vm_map_unlock(map) _vm_map_unlock(map, LOCK_FILE,
LOCK_LINE)
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