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Date:      Thu, 17 Dec 2015 17:48:57 +0000 (UTC)
From:      "Conrad E. Meyer" <cem@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r292406 - head/sys/vm
Message-ID:  <201512171748.tBHHmvAC037349@repo.freebsd.org>
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Author: cem
Date: Thu Dec 17 17:48:57 2015
New Revision: 292406
URL: https://svnweb.freebsd.org/changeset/base/292406

Log:
  vm_page_replace: add wrapper to KASSERT about old page
  
  It turns out the callers of vm_page_replace know exactly which page they are
  replacing and would like to assert about it.  Change those from hard panics to
  KASSERTs, and provide them with a wrapper so they don't have to deal with
  warnings from an INVARIANTS-dependent dead store of the return value of
  vm_page_replace.
  
  Submitted by:	Ryan Libby <rlibby@gmail.com>
  Reviewed by:	alc, kib (earlier version)
  Sponsored by:	EMC / Isilon Storage Division
  Differential Revision:	https://reviews.freebsd.org/D4497

Modified:
  head/sys/vm/device_pager.c
  head/sys/vm/sg_pager.c
  head/sys/vm/vm_page.h

Modified: head/sys/vm/device_pager.c
==============================================================================
--- head/sys/vm/device_pager.c	Thu Dec 17 17:00:04 2015	(r292405)
+++ head/sys/vm/device_pager.c	Thu Dec 17 17:48:57 2015	(r292406)
@@ -347,8 +347,7 @@ old_dev_pager_fault(vm_object_t object, 
 		 */
 		page = vm_page_getfake(paddr, memattr);
 		VM_OBJECT_WLOCK(object);
-		if (vm_page_replace(page, object, (*mres)->pindex) != *mres)
-			panic("old_dev_pager_fault: invalid page replacement");
+		vm_page_replace_checked(page, object, (*mres)->pindex, *mres);
 		vm_page_lock(*mres);
 		vm_page_free(*mres);
 		vm_page_unlock(*mres);

Modified: head/sys/vm/sg_pager.c
==============================================================================
--- head/sys/vm/sg_pager.c	Thu Dec 17 17:00:04 2015	(r292405)
+++ head/sys/vm/sg_pager.c	Thu Dec 17 17:48:57 2015	(r292406)
@@ -188,8 +188,7 @@ sg_pager_getpages(vm_object_t object, vm
 	page = vm_page_getfake(paddr, memattr);
 	VM_OBJECT_WLOCK(object);
 	TAILQ_INSERT_TAIL(&object->un_pager.sgp.sgp_pglist, page, plinks.q);
-	if (vm_page_replace(page, object, offset) != m[0])
-		panic("sg_pager_getpages: invalid place replacement");
+	vm_page_replace_checked(page, object, offset, m[0]);
 	m[0] = page;
 	page->valid = VM_PAGE_BITS_ALL;
 

Modified: head/sys/vm/vm_page.h
==============================================================================
--- head/sys/vm/vm_page.h	Thu Dec 17 17:00:04 2015	(r292405)
+++ head/sys/vm/vm_page.h	Thu Dec 17 17:48:57 2015	(r292406)
@@ -678,5 +678,20 @@ vm_page_undirty(vm_page_t m)
 	m->dirty = 0;
 }
 
+static inline void
+vm_page_replace_checked(vm_page_t mnew, vm_object_t object, vm_pindex_t pindex,
+    vm_page_t mold)
+{
+	vm_page_t mret;
+
+	mret = vm_page_replace(mnew, object, pindex);
+	KASSERT(mret == mold,
+	    ("invalid page replacement, mold=%p, mret=%p", mold, mret));
+
+	/* Unused if !INVARIANTS. */
+	(void)mold;
+	(void)mret;
+}
+
 #endif				/* _KERNEL */
 #endif				/* !_VM_PAGE_ */

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