svn commit: r351235 - head/sys/vm

[Jeff Roberson]

Author: jeff
Date: Mon Aug 19 22:25:28 2019
New Revision: 351235
URL: https://svnweb.freebsd.org/changeset/base/351235

Log:
  Permit vm_pager_has_page() to run with a shared lock.  Introduce
  VM_OBJECT_DROP/VM_OBJECT_PICKUP to handle functions that are called with
  uncertain lock state.
  
  Reviewed by:	kib, markj
  Tested by:	pho
  Sponsored by:	Netflix
  Differential Revision:	https://reviews.freebsd.org/D21310

Modified:
  head/sys/vm/vm_object.h
  head/sys/vm/vm_pager.h
  head/sys/vm/vnode_pager.c

Modified: head/sys/vm/vm_object.h
==============================================================================
--- head/sys/vm/vm_object.h	Mon Aug 19 21:59:02 2019	(r351234)
+++ head/sys/vm/vm_object.h	Mon Aug 19 22:25:28 2019	(r351235)
@@ -255,6 +255,10 @@ extern struct vm_object kernel_object_store;
 	rw_wowned(&(object)->lock)
 #define	VM_OBJECT_WUNLOCK(object)					\
 	rw_wunlock(&(object)->lock)
+#define	VM_OBJECT_DROP(object)						\
+	lock_class_rw.lc_unlock(&(object)->lock.lock_object)
+#define	VM_OBJECT_PICKUP(object, state)					\
+	lock_class_rw.lc_lock(&(object)->lock.lock_object, (state))
 
 struct vnode;
 

Modified: head/sys/vm/vm_pager.h
==============================================================================
--- head/sys/vm/vm_pager.h	Mon Aug 19 21:59:02 2019	(r351234)
+++ head/sys/vm/vm_pager.h	Mon Aug 19 22:25:28 2019	(r351235)
@@ -151,7 +151,7 @@ vm_pager_has_page(
 ) {
 	boolean_t ret;
 
-	VM_OBJECT_ASSERT_WLOCKED(object);
+	VM_OBJECT_ASSERT_LOCKED(object);
 	ret = (*pagertab[object->type]->pgo_haspage)
 	    (object, offset, before, after);
 	return (ret);

Modified: head/sys/vm/vnode_pager.c
==============================================================================
--- head/sys/vm/vnode_pager.c	Mon Aug 19 21:59:02 2019	(r351234)
+++ head/sys/vm/vnode_pager.c	Mon Aug 19 22:25:28 2019	(r351235)
@@ -355,13 +355,14 @@ vnode_pager_haspage(vm_object_t object, vm_pindex_t pi
 {
 	struct vnode *vp = object->handle;
 	daddr_t bn;
+	uintptr_t lockstate;
 	int err;
 	daddr_t reqblock;
 	int poff;
 	int bsize;
 	int pagesperblock, blocksperpage;
 
-	VM_OBJECT_ASSERT_WLOCKED(object);
+	VM_OBJECT_ASSERT_LOCKED(object);
 	/*
 	 * If no vp or vp is doomed or marked transparent to VM, we do not
 	 * have the page.
@@ -384,9 +385,9 @@ vnode_pager_haspage(vm_object_t object, vm_pindex_t pi
 		blocksperpage = (PAGE_SIZE / bsize);
 		reqblock = pindex * blocksperpage;
 	}
-	VM_OBJECT_WUNLOCK(object);
+	lockstate = VM_OBJECT_DROP(object);
 	err = VOP_BMAP(vp, reqblock, NULL, &bn, after, before);
-	VM_OBJECT_WLOCK(object);
+	VM_OBJECT_PICKUP(object, lockstate);
 	if (err)
 		return TRUE;
 	if (bn == -1)