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Index: head/sys/vm/vm_fault.c
===================================================================
--- head/sys/vm/vm_fault.c
+++ head/sys/vm/vm_fault.c
@@ -342,10 +342,10 @@
*m_hold = m;
vm_page_wire(m);
}
- vm_fault_dirty(fs->entry, m, prot, fault_type, fault_flags);
if (psind == 0 && !wired)
vm_fault_prefault(fs, vaddr, PFBAK, PFFOR, true);
VM_OBJECT_RUNLOCK(fs->first_object);
+ vm_fault_dirty(fs->entry, m, prot, fault_type, fault_flags);
vm_map_lookup_done(fs->map, fs->entry);
curthread->td_ru.ru_minflt++;
@@ -632,7 +632,7 @@
}
static int
-vm_fault_lock_vnode(struct faultstate *fs)
+vm_fault_lock_vnode(struct faultstate *fs, bool objlocked)
{
struct vnode *vp;
int error, locked;
@@ -668,7 +668,10 @@
}
vhold(vp);
- unlock_and_deallocate(fs);
+ if (objlocked)
+ unlock_and_deallocate(fs);
+ else
+ fault_deallocate(fs);
error = vget(vp, locked | LK_RETRY | LK_CANRECURSE, curthread);
vdrop(vp);
fs->vp = vp;
@@ -863,9 +866,11 @@
*/
if (!vm_page_all_valid(fs.m))
goto readrest;
- break; /* break to PAGE HAS BEEN FOUND */
+ VM_OBJECT_WUNLOCK(fs.object);
+ break; /* break to PAGE HAS BEEN FOUND. */
}
KASSERT(fs.m == NULL, ("fs.m should be NULL, not %p", fs.m));
+ VM_OBJECT_ASSERT_WLOCKED(fs.object);
/*
* Page is not resident. If the pager might contain the page
@@ -876,7 +881,7 @@
if (fs.object->type != OBJT_DEFAULT ||
fs.object == fs.first_object) {
if ((fs.object->flags & OBJ_SIZEVNLOCK) != 0) {
- rv = vm_fault_lock_vnode(&fs);
+ rv = vm_fault_lock_vnode(&fs, true);
MPASS(rv == KERN_SUCCESS ||
rv == KERN_RESOURCE_SHORTAGE);
if (rv == KERN_RESOURCE_SHORTAGE)
@@ -956,12 +961,23 @@
readrest:
/*
+ * Default objects have no pager so no exclusive busy exists
+ * to protect this page in the chain. Skip to the next
+ * object without dropping the lock to preserve atomicity of
+ * shadow faults.
+ */
+ if (fs.object->type == OBJT_DEFAULT)
+ goto next;
+
+ /*
* At this point, we have either allocated a new page or found
* an existing page that is only partially valid.
*
* We hold a reference on the current object and the page is
- * exclusive busied.
+ * exclusive busied. The exclusive busy prevents simultaneous
+ * faults and collapses while the object lock is dropped.
*/
+ VM_OBJECT_WUNLOCK(fs.object);
/*
* If the pager for the current object might have the page,
@@ -972,8 +988,7 @@
* have the page, the number of additional pages to read will
* apply to subsequent objects in the shadow chain.
*/
- if (fs.object->type != OBJT_DEFAULT && nera == -1 &&
- !P_KILLED(curproc)) {
+ if (nera == -1 && !P_KILLED(curproc)) {
KASSERT(fs.lookup_still_valid, ("map unlocked"));
era = fs.entry->read_ahead;
behavior = vm_map_entry_behavior(fs.entry);
@@ -1039,7 +1054,7 @@
*/
unlock_map(&fs);
- rv = vm_fault_lock_vnode(&fs);
+ rv = vm_fault_lock_vnode(&fs, false);
MPASS(rv == KERN_SUCCESS ||
rv == KERN_RESOURCE_SHORTAGE);
if (rv == KERN_RESOURCE_SHORTAGE)
@@ -1080,15 +1095,14 @@
}
ahead = ulmin(ahead, atop(e_end - vaddr) - 1);
}
- VM_OBJECT_WUNLOCK(fs.object);
rv = vm_pager_get_pages(fs.object, &fs.m, 1,
&behind, &ahead);
- VM_OBJECT_WLOCK(fs.object);
if (rv == VM_PAGER_OK) {
faultcount = behind + 1 + ahead;
hardfault = true;
- break; /* break to PAGE HAS BEEN FOUND */
+ break; /* break to PAGE HAS BEEN FOUND. */
}
+ VM_OBJECT_WLOCK(fs.object);
if (rv == VM_PAGER_ERROR)
printf("vm_fault: pager read error, pid %d (%s)\n",
curproc->p_pid, curproc->p_comm);
@@ -1106,6 +1120,7 @@
}
+next:
/*
* The requested page does not exist at this object/
* offset. Remove the invalid page from the object,
@@ -1126,19 +1141,18 @@
* Move on to the next object. Lock the next object before
* unlocking the current one.
*/
+ VM_OBJECT_ASSERT_WLOCKED(fs.object);
next_object = fs.object->backing_object;
if (next_object == NULL) {
/*
* If there's no object left, fill the page in the top
* object with zeros.
*/
+ VM_OBJECT_WUNLOCK(fs.object);
if (fs.object != fs.first_object) {
vm_object_pip_wakeup(fs.object);
- VM_OBJECT_WUNLOCK(fs.object);
-
fs.object = fs.first_object;
fs.pindex = fs.first_pindex;
- VM_OBJECT_WLOCK(fs.object);
}
MPASS(fs.first_m != NULL);
MPASS(fs.m == NULL);
@@ -1157,7 +1171,7 @@
vm_page_valid(fs.m);
/* Don't try to prefault neighboring pages. */
faultcount = 1;
- break; /* break to PAGE HAS BEEN FOUND */
+ break; /* break to PAGE HAS BEEN FOUND. */
} else {
MPASS(fs.first_m != NULL);
KASSERT(fs.object != next_object,
@@ -1173,12 +1187,12 @@
}
}
- vm_page_assert_xbusied(fs.m);
-
/*
- * PAGE HAS BEEN FOUND. [Loop invariant still holds -- the object lock
- * is held.]
+ * PAGE HAS BEEN FOUND. A valid page has been found and exclusively
+ * busied. The object lock must no longer be held.
*/
+ vm_page_assert_xbusied(fs.m);
+ VM_OBJECT_ASSERT_UNLOCKED(fs.object);
/*
* If the page is being written, but isn't already owned by the
@@ -1202,27 +1216,28 @@
*/
is_first_object_locked = false;
if (
- /*
- * Only one shadow object
- */
- (fs.object->shadow_count == 1) &&
- /*
- * No COW refs, except us
- */
- (fs.object->ref_count == 1) &&
- /*
- * No one else can look this object up
- */
- (fs.object->handle == NULL) &&
- /*
- * No other ways to look the object up
- */
- ((fs.object->flags & OBJ_ANON) != 0) &&
+ /*
+ * Only one shadow object
+ */
+ fs.object->shadow_count == 1 &&
+ /*
+ * No COW refs, except us
+ */
+ fs.object->ref_count == 1 &&
+ /*
+ * No one else can look this object up
+ */
+ fs.object->handle == NULL &&
+ /*
+ * No other ways to look the object up
+ */
+ (fs.object->flags & OBJ_ANON) != 0 &&
(is_first_object_locked = VM_OBJECT_TRYWLOCK(fs.first_object)) &&
- /*
- * We don't chase down the shadow chain
- */
- fs.object == fs.first_object->backing_object) {
+ /*
+ * We don't chase down the shadow chain
+ */
+ fs.object == fs.first_object->backing_object &&
+ VM_OBJECT_TRYWLOCK(fs.object)) {
/*
* Remove but keep xbusy for replace. fs.m is
@@ -1242,11 +1257,13 @@
fs.first_object->backing_object_offset));
#endif
VM_OBJECT_WUNLOCK(fs.object);
+ VM_OBJECT_WUNLOCK(fs.first_object);
fs.first_m = fs.m;
fs.m = NULL;
VM_CNT_INC(v_cow_optim);
} else {
- VM_OBJECT_WUNLOCK(fs.object);
+ if (is_first_object_locked)
+ VM_OBJECT_WUNLOCK(fs.first_object);
/*
* Oh, well, lets copy it.
*/
@@ -1285,8 +1302,6 @@
fs.object = fs.first_object;
fs.pindex = fs.first_pindex;
fs.m = fs.first_m;
- if (!is_first_object_locked)
- VM_OBJECT_WLOCK(fs.object);
VM_CNT_INC(v_cow_faults);
curthread->td_cow++;
} else {
@@ -1300,7 +1315,7 @@
*/
if (!fs.lookup_still_valid) {
if (!vm_map_trylock_read(fs.map)) {
- unlock_and_deallocate(&fs);
+ fault_deallocate(&fs);
goto RetryFault;
}
fs.lookup_still_valid = true;
@@ -1314,7 +1329,7 @@
* pageout will grab it eventually.
*/
if (result != KERN_SUCCESS) {
- unlock_and_deallocate(&fs);
+ fault_deallocate(&fs);
/*
* If retry of map lookup would have blocked then
@@ -1326,7 +1341,7 @@
}
if ((retry_object != fs.first_object) ||
(retry_pindex != fs.first_pindex)) {
- unlock_and_deallocate(&fs);
+ fault_deallocate(&fs);
goto RetryFault;
}
@@ -1341,7 +1356,7 @@
prot &= retry_prot;
fault_type &= retry_prot;
if (prot == 0) {
- unlock_and_deallocate(&fs);
+ fault_deallocate(&fs);
goto RetryFault;
}
@@ -1350,6 +1365,7 @@
("!wired && VM_FAULT_WIRE"));
}
}
+ VM_OBJECT_ASSERT_UNLOCKED(fs.object);
/*
* If the page was filled by a pager, save the virtual address that
@@ -1360,17 +1376,16 @@
if (hardfault)
fs.entry->next_read = vaddr + ptoa(ahead) + PAGE_SIZE;
- vm_page_assert_xbusied(fs.m);
- vm_fault_dirty(fs.entry, fs.m, prot, fault_type, fault_flags);
-
/*
* Page must be completely valid or it is not fit to
* map into user space. vm_pager_get_pages() ensures this.
*/
+ vm_page_assert_xbusied(fs.m);
KASSERT(vm_page_all_valid(fs.m),
("vm_fault: page %p partially invalid", fs.m));
- VM_OBJECT_WUNLOCK(fs.object);
+ vm_fault_dirty(fs.entry, fs.m, prot, fault_type, fault_flags);
+
/*
* Put this page into the physical map. We had to do the unlock above
* because pmap_enter() may sleep. We don't put the page
@@ -1451,17 +1466,11 @@
vm_size_t size;
object = fs->object;
- VM_OBJECT_ASSERT_WLOCKED(object);
+ VM_OBJECT_ASSERT_UNLOCKED(object);
first_object = fs->first_object;
- if (first_object != object) {
- if (!VM_OBJECT_TRYWLOCK(first_object)) {
- VM_OBJECT_WUNLOCK(object);
- VM_OBJECT_WLOCK(first_object);
- VM_OBJECT_WLOCK(object);
- }
- }
/* Neither fictitious nor unmanaged pages can be reclaimed. */
if ((first_object->flags & (OBJ_FICTITIOUS | OBJ_UNMANAGED)) == 0) {
+ VM_OBJECT_RLOCK(first_object);
size = VM_FAULT_DONTNEED_MIN;
if (MAXPAGESIZES > 1 && size < pagesizes[1])
size = pagesizes[1];
@@ -1501,9 +1510,8 @@
vm_page_deactivate(m);
}
}
+ VM_OBJECT_RUNLOCK(first_object);
}
- if (first_object != object)
- VM_OBJECT_WUNLOCK(first_object);
}
/*

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