vm_page_free_invalid(): Relax the xbusy assertion.

vm_page_assert_xbusied() asserts that the busying thread is the current
thread.  For some uses of vm_page_free_invalid() (e.g., error handling
in vnode_pager_generic_getpages_done()), this condition might not hold.

Reported by:	Jenkins via trasz
Reviewed by:	chs, kib
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D25828

1 files changed, 6 insertions, 1 deletions

diff --git a/sys/vm/vm_page.c b/sys/vm/vm_page.c
index a7d6f3dd9d64..8c2df3e78e17 100644
--- a/sys/vm/vm_page.c
+++ b/sys/vm/vm_page.c
@@ -1371,11 +1371,16 @@ vm_page_free_invalid(vm_page_t m)
 
 	KASSERT(vm_page_none_valid(m), ("page %p is valid", m));
 	KASSERT(!pmap_page_is_mapped(m), ("page %p is mapped", m));
-	vm_page_assert_xbusied(m);
 	KASSERT(m->object != NULL, ("page %p has no object", m));
 	VM_OBJECT_ASSERT_WLOCKED(m->object);
 
 	/*
+	 * We may be attempting to free the page as part of the handling for an
+	 * I/O error, in which case the page was xbusied by a different thread.
+	 */
+	vm_page_xbusy_claim(m);
+
+	/*
 	 * If someone has wired this page while the object lock
 	 * was not held, then the thread that unwires is responsible
 	 * for freeing the page.  Otherwise just free the page now.