Addendum to r254141: The call to vm_radix_insert() in vm_page_cache() can

reclaim the last preexisting cached page in the object, resulting in a call
to vdrop().  Detect this scenario so that the vnode's hold count is
correctly maintained.  Otherwise, we panic.

Reported by:	scottl
Tested by:	pho
Discussed with:	attilio, jeff, kib

1 files changed, 9 insertions, 0 deletions

diff --git a/sys/vm/vm_page.c b/sys/vm/vm_page.c
index 1241775..2177289 100644
--- a/sys/vm/vm_page.c
+++ b/sys/vm/vm_page.c
@@ -2558,6 +2558,15 @@ vm_page_cache(vm_page_t m)
 		vm_page_free(m);
 		return;
 	}
+
+	/*
+	 * The above call to vm_radix_insert() could reclaim the one pre-
+	 * existing cached page from this object, resulting in a call to
+	 * vdrop().
+	 */
+	if (!cache_was_empty)
+		cache_was_empty = vm_radix_is_singleton(&object->cache);
+
 	m->flags |= PG_CACHED;
 	cnt.v_cache_count++;
 	PCPU_INC(cnt.v_tcached);