diff options
-rw-r--r-- | sys/vm/vm_fault.c | 23 |
1 files changed, 15 insertions, 8 deletions
diff --git a/sys/vm/vm_fault.c b/sys/vm/vm_fault.c index 7581cc8..acd4448 100644 --- a/sys/vm/vm_fault.c +++ b/sys/vm/vm_fault.c @@ -1229,7 +1229,7 @@ vm_fault_copy_entry(vm_map_t dst_map, vm_map_t src_map, vm_offset_t vaddr; vm_page_t dst_m; vm_page_t src_m; - boolean_t src_readonly, upgrade; + boolean_t upgrade; #ifdef lint src_map++; @@ -1239,7 +1239,6 @@ vm_fault_copy_entry(vm_map_t dst_map, vm_map_t src_map, src_object = src_entry->object.vm_object; src_pindex = OFF_TO_IDX(src_entry->offset); - src_readonly = (src_entry->protection & VM_PROT_WRITE) == 0; /* * Create the top-level object for the destination entry. (Doesn't @@ -1310,25 +1309,33 @@ vm_fault_copy_entry(vm_map_t dst_map, vm_map_t src_map, /* * Find the page in the source object, and copy it in. - * (Because the source is wired down, the page will be in - * memory.) + * Because the source is wired down, the page will be + * in memory. */ VM_OBJECT_RLOCK(src_object); object = src_object; pindex = src_pindex + dst_pindex; while ((src_m = vm_page_lookup(object, pindex)) == NULL && - src_readonly && (backing_object = object->backing_object) != NULL) { /* - * Allow fallback to backing objects if we are reading. + * Unless the source mapping is read-only or + * it is presently being upgraded from + * read-only, the first object in the shadow + * chain should provide all of the pages. In + * other words, this loop body should never be + * executed when the source mapping is already + * read/write. */ + KASSERT((src_entry->protection & VM_PROT_WRITE) == 0 || + upgrade, + ("vm_fault_copy_entry: main object missing page")); + VM_OBJECT_RLOCK(backing_object); pindex += OFF_TO_IDX(object->backing_object_offset); VM_OBJECT_RUNLOCK(object); object = backing_object; } - if (src_m == NULL) - panic("vm_fault_copy_wired: page missing"); + KASSERT(src_m != NULL, ("vm_fault_copy_entry: page missing")); pmap_copy_page(src_m, dst_m); VM_OBJECT_RUNLOCK(object); dst_m->valid = VM_PAGE_BITS_ALL; |