From owner-svn-src-all@freebsd.org Thu Nov 3 16:44:57 2016 Return-Path: Delivered-To: svn-src-all@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 588D4C2D80A; Thu, 3 Nov 2016 16:44:57 +0000 (UTC) (envelope-from alc@FreeBSD.org) Received: from repo.freebsd.org (repo.freebsd.org [IPv6:2610:1c1:1:6068::e6a:0]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id CDCF412DF; Thu, 3 Nov 2016 16:44:56 +0000 (UTC) (envelope-from alc@FreeBSD.org) Received: from repo.freebsd.org ([127.0.1.37]) by repo.freebsd.org (8.15.2/8.15.2) with ESMTP id uA3GitCd062286; Thu, 3 Nov 2016 16:44:55 GMT (envelope-from alc@FreeBSD.org) Received: (from alc@localhost) by repo.freebsd.org (8.15.2/8.15.2/Submit) id uA3Git4u062285; Thu, 3 Nov 2016 16:44:55 GMT (envelope-from alc@FreeBSD.org) Message-Id: <201611031644.uA3Git4u062285@repo.freebsd.org> X-Authentication-Warning: repo.freebsd.org: alc set sender to alc@FreeBSD.org using -f From: Alan Cox Date: Thu, 3 Nov 2016 16:44:55 +0000 (UTC) To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r308261 - head/sys/vm X-SVN-Group: head MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 03 Nov 2016 16:44:57 -0000 Author: alc Date: Thu Nov 3 16:44:55 2016 New Revision: 308261 URL: https://svnweb.freebsd.org/changeset/base/308261 Log: In vm_fault()'s loop over the shadow chain, move a comment describing our invariants to a better place. Also, add two comments concerning the relationship between the map and vnode locks. Reviewed by: kib MFC after: 3 days Modified: head/sys/vm/vm_fault.c Modified: head/sys/vm/vm_fault.c ============================================================================== --- head/sys/vm/vm_fault.c Thu Nov 3 15:04:16 2016 (r308260) +++ head/sys/vm/vm_fault.c Thu Nov 3 16:44:55 2016 (r308261) @@ -564,6 +564,14 @@ fast_failed: readrest: /* + * At this point, we have either allocated a new page or found + * an existing page that is only partially valid. + * + * We hold a reference on the current object and the page is + * exclusive busied. + */ + + /* * If the pager for the current object might have the page, * then determine the number of additional pages to read and * potentially reprioritize previously read pages for earlier @@ -632,18 +640,23 @@ readrest: */ if (fs.object->type != OBJT_DEFAULT) { /* - * We have either allocated a new page or found an - * existing page that is only partially valid. We - * hold a reference on fs.object and the page is - * exclusive busied. + * Release the map lock before locking the vnode or + * sleeping in the pager. (If the current object has + * a shadow, then an earlier iteration of this loop + * may have already unlocked the map.) */ unlock_map(&fs); if (fs.object->type == OBJT_VNODE && (vp = fs.object->handle) != fs.vp) { + /* + * Perform an unlock in case the desired vnode + * changed while the map was unlocked during a + * retry. + */ unlock_vp(&fs); - locked = VOP_ISLOCKED(vp); + locked = VOP_ISLOCKED(vp); if (locked != LK_EXCLUSIVE) locked = LK_SHARED;