Fix a BUF_TIMELOCK race against BUF_LOCK and fix a deadlock in vget()

against VM_WAIT in the pageout code.  Both fixes involve adjusting
the lockmgr's timeout capability so locks obtained with timeouts do not
interfere with locks obtained without a timeout.

Hopefully MFC: before the 4.5 release

1 files changed, 11 insertions, 4 deletions

diff --git a/sys/vm/vm_pageout.c b/sys/vm/vm_pageout.c
index 73ef06d..47ce9e8 100644
--- a/sys/vm/vm_pageout.c
+++ b/sys/vm/vm_pageout.c
@@ -193,6 +193,10 @@ SYSCTL_INT(_vm, OID_AUTO, defer_swapspace_pageouts,
 SYSCTL_INT(_vm, OID_AUTO, disable_swapspace_pageouts,
 	CTLFLAG_RW, &disable_swap_pageouts, 0, "Disallow swapout of dirty pages");
 
+static int pageout_lock_miss;
+SYSCTL_INT(_vm, OID_AUTO, pageout_lock_miss,
+	CTLFLAG_RD, &pageout_lock_miss, 0, "vget() lock misses during pageout");
+
 #define VM_PAGEOUT_PAGE_COUNT 16
 int vm_pageout_page_count = VM_PAGEOUT_PAGE_COUNT;
 
@@ -860,17 +864,20 @@ rescan0:
 			 * way too large a weighting to defering the freeing
 			 * of dirty pages.
 			 *
-			 * XXX we need to be able to apply a timeout to the
-			 * vget() lock attempt.
+			 * We can't wait forever for the vnode lock, we might
+			 * deadlock due to a vn_read() getting stuck in
+			 * vm_wait while holding this vnode.  We skip the 
+			 * vnode if we can't get it in a reasonable amount
+			 * of time.
 			 */
-
 			if (object->type == OBJT_VNODE) {
 				vp = object->handle;
 
 				mp = NULL;
 				if (vp->v_type == VREG)
 					vn_start_write(vp, &mp, V_NOWAIT);
-				if (vget(vp, LK_EXCLUSIVE|LK_NOOBJ, curthread)) {
+				if (vget(vp, LK_EXCLUSIVE|LK_NOOBJ|LK_TIMELOCK, curthread)) {
+					++pageout_lock_miss;
 					vn_finished_write(mp);
 					if (object->flags & OBJ_MIGHTBEDIRTY)
 						vnodes_skipped++;