svn commit: r265002 - head/sys/vm
Konstantin Belousov
kib at FreeBSD.org
Sun Apr 27 05:19:02 UTC 2014
Author: kib
Date: Sun Apr 27 05:19:01 2014
New Revision: 265002
URL: http://svnweb.freebsd.org/changeset/base/265002
Log:
When vm_fault_copy_entry() is called from vm_map_protect() for a wired
entry and performs the upgrade of the entry permissions from read-only
to read-write, we must allow to search for the source pages in the
backing object, like we do in the case of forking the read-only wired
entry. For the fork case, the behaviour is allowed by src_readonly
boolean, which in fact is only used to assert that read-write case
provides all source pages in the top-level object.
Eliminate the src_readonly variable. Allow for the copy loop to look
into the backing objects, add explicit asserts to ensure that only
read-only and upgrade case actually does.
Expand comments. Change the panic call into assert.
Reported by: markj
Tested by: markj, pho (previous version)
Reviewed by: alc
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Modified:
head/sys/vm/vm_fault.c
Modified: head/sys/vm/vm_fault.c
==============================================================================
--- head/sys/vm/vm_fault.c Sun Apr 27 02:28:32 2014 (r265001)
+++ head/sys/vm/vm_fault.c Sun Apr 27 05:19:01 2014 (r265002)
@@ -1240,7 +1240,7 @@ vm_fault_copy_entry(vm_map_t dst_map, vm
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++;
@@ -1250,7 +1250,6 @@ vm_fault_copy_entry(vm_map_t dst_map, vm
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
@@ -1321,25 +1320,33 @@ vm_fault_copy_entry(vm_map_t dst_map, vm
/*
* 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;
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