(1/6) Replace busy checks with acquires where it is trival to do so.

This is the first in a series of patches that promotes the page busy field
to a first class lock that no longer requires the object lock for
consistency.

Reviewed by:	kib, markj
Tested by:	pho
Sponsored by:	Netflix, Intel
Differential Revision:	https://reviews.freebsd.org/D21548

1 files changed, 5 insertions, 1 deletions

diff --git a/sys/kern/kern_exec.c b/sys/kern/kern_exec.c
index 5abced8fbbaa..e1c647ca4f00 100644
--- a/sys/kern/kern_exec.c
+++ b/sys/kern/kern_exec.c
@@ -976,10 +976,14 @@ exec_map_first_page(struct image_params *imgp)
 #if VM_NRESERVLEVEL > 0
 	vm_object_color(object, 0);
 #endif
+retry:
 	ma[0] = vm_page_grab(object, 0, VM_ALLOC_NORMAL | VM_ALLOC_NOBUSY |
 	    VM_ALLOC_WIRED);
 	if (ma[0]->valid != VM_PAGE_BITS_ALL) {
-		vm_page_xbusy(ma[0]);
+		if (vm_page_busy_acquire(ma[0], VM_ALLOC_WAITFAIL) == 0) {
+			vm_page_unwire_noq(ma[0]);
+			goto retry;
+		}
 		if (!vm_pager_has_page(object, 0, NULL, &after)) {
 			if (vm_page_unwire_noq(ma[0]))
 				vm_page_free(ma[0]);