VM: improve pageout deadlock workaround

Commit 5dd4f67522ad0d49a2cecdb9b109251f546d4dd1 makes VM map entry
allocation done with VM privilege, so that a VM map isn't held locked
while physical allocations are paused, which may block the default
pager during page eviction, causing a system-wide deadlock.

First, it turns out that map entries aren't the only buffers allocated,
and second, their number can't be easily determined, which makes a
preallocation strategy very hard to implement.

This change generalizes the strategy of VM privilege increase when a
VM map is locked.

* device/ds_routines.c (io_done_thread): Use integer values instead
of booleans when setting VM privilege.
* kern/thread.c (thread_init, thread_wire): Likewise.
* vm/vm_pageout.c (vm_pageout): Likewise.
* kern/thread.h (struct thread): Turn member `vm_privilege' into an
unsigned integer.
* vm/vm_map.c (vm_map_lock): New function, where VM privilege is
temporarily increased.
(vm_map_unlock): New function, where VM privilege is decreased.
(_vm_map_entry_create): Remove VM privilege workaround from this
function.
* vm/vm_map.h (vm_map_lock, vm_map_unlock): Turn into functions.

1 files changed, 3 insertions, 3 deletions

diff --git a/kern/thread.c b/kern/thread.c
index 7db1f3d2..0ac7c535 100644
--- a/kern/thread.c
+++ b/kern/thread.c
@@ -342,7 +342,7 @@ void thread_init(void)
 	/* thread_template.sched_stamp (later) */
 
 	thread_template.recover = (vm_offset_t) 0;
-	thread_template.vm_privilege = FALSE;
+	thread_template.vm_privilege = 0;
 
 	thread_template.user_stop_count = 1;
 
@@ -2233,11 +2233,11 @@ thread_wire(
 	thread_lock(thread);
 
 	if (wired) {
-	    thread->vm_privilege = TRUE;
+	    thread->vm_privilege = 1;
 	    stack_privilege(thread);
 	}
 	else {
-	    thread->vm_privilege = FALSE;
+	    thread->vm_privilege = 0;
 /*XXX	    stack_unprivilege(thread); */
 	    thread->stack_privilege = 0;
 	}