diff options
author | kib <kib@FreeBSD.org> | 2009-02-08 20:00:33 +0000 |
---|---|---|
committer | kib <kib@FreeBSD.org> | 2009-02-08 20:00:33 +0000 |
commit | 6f193f1588fc869ceaf793da8451dda84fe05fbd (patch) | |
tree | 0f22976ed0ca5bf3837accaee2c0e5a4d01e9cfb /sys/vm/vm_map.c | |
parent | 2d39ccdd942bb55bc8f71573ef8547fdc75623ee (diff) | |
download | FreeBSD-src-6f193f1588fc869ceaf793da8451dda84fe05fbd.zip FreeBSD-src-6f193f1588fc869ceaf793da8451dda84fe05fbd.tar.gz |
Add the comments to vm_map_simplify_entry() and vmspace_fork(),
describing why several calls to vm_deallocate_object() with locked map
do not result in the acquisition of the vnode lock after map lock.
Suggested and reviewed by: tegge
Diffstat (limited to 'sys/vm/vm_map.c')
-rw-r--r-- | sys/vm/vm_map.c | 20 |
1 files changed, 20 insertions, 0 deletions
diff --git a/sys/vm/vm_map.c b/sys/vm/vm_map.c index b173fdd..13b9050 100644 --- a/sys/vm/vm_map.c +++ b/sys/vm/vm_map.c @@ -1350,6 +1350,16 @@ vm_map_simplify_entry(vm_map_t map, vm_map_entry_t entry) entry->offset = prev->offset; if (entry->prev != &map->header) vm_map_entry_resize_free(map, entry->prev); + + /* + * If the backing object is the vnode object, + * vm_object_deallocate() results in a call to + * vrele(). Because the reference to the + * object is not last, vrele() does not lock + * the vnode, and map lock can be kept without + * causing vnode lock to be taken after the + * map lock. + */ if (prev->object.vm_object) vm_object_deallocate(prev->object.vm_object); vm_map_entry_dispose(map, prev); @@ -1371,6 +1381,10 @@ vm_map_simplify_entry(vm_map_t map, vm_map_entry_t entry) vm_map_entry_unlink(map, next); entry->end = next->end; vm_map_entry_resize_free(map, entry); + + /* + * See comment above. + */ if (next->object.vm_object) vm_object_deallocate(next->object.vm_object); vm_map_entry_dispose(map, next); @@ -2729,6 +2743,12 @@ vmspace_fork(struct vmspace *vm1) /* Transfer the second reference too. */ vm_object_reference( old_entry->object.vm_object); + + /* + * As in vm_map_simplify_entry(), the + * vnode lock may not be acquired in + * this call to vm_object_deallocate(). + */ vm_object_deallocate(object); object = old_entry->object.vm_object; } |