From owner-svn-src-all@freebsd.org Tue Nov 1 17:11:11 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 DD6D7C2919F; Tue, 1 Nov 2016 17:11:11 +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 8C3C8175F; Tue, 1 Nov 2016 17:11:11 +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 uA1HBAWH043696; Tue, 1 Nov 2016 17:11:10 GMT (envelope-from alc@FreeBSD.org) Received: (from alc@localhost) by repo.freebsd.org (8.15.2/8.15.2/Submit) id uA1HBAKR043695; Tue, 1 Nov 2016 17:11:10 GMT (envelope-from alc@FreeBSD.org) Message-Id: <201611011711.uA1HBAKR043695@repo.freebsd.org> X-Authentication-Warning: repo.freebsd.org: alc set sender to alc@FreeBSD.org using -f From: Alan Cox Date: Tue, 1 Nov 2016 17:11:10 +0000 (UTC) To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r308174 - 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: Tue, 01 Nov 2016 17:11:12 -0000 Author: alc Date: Tue Nov 1 17:11:10 2016 New Revision: 308174 URL: https://svnweb.freebsd.org/changeset/base/308174 Log: Move and revise a comment about the relation between the object's paging- in-progress count and the vnode. Prior to r188331, we always acquired the vnode lock before incrementing the object's paging-in-progress count. Now, we increment it before attempting to acquire the vnode lock with LK_NOWAIT, but we never sleep acquiring the vnode lock while we have the count incremented. 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 Tue Nov 1 16:03:31 2016 (r308173) +++ head/sys/vm/vm_fault.c Tue Nov 1 17:11:10 2016 (r308174) @@ -420,8 +420,7 @@ fast_failed: * they will stay around as well. * * Bump the paging-in-progress count to prevent size changes (e.g. - * truncation operations) during I/O. This must be done after - * obtaining the vnode lock in order to avoid possible deadlocks. + * truncation operations) during I/O. */ vm_object_reference_locked(fs.first_object); vm_object_pip_add(fs.first_object, 1); @@ -647,7 +646,13 @@ readrest: if (locked != LK_EXCLUSIVE) locked = LK_SHARED; - /* Do not sleep for vnode lock while fs.m is busy */ + + /* + * We must not sleep acquiring the vnode lock + * while we have the page exclusive busied or + * the object's paging-in-progress count + * incremented. Otherwise, we could deadlock. + */ error = vget(vp, locked | LK_CANRECURSE | LK_NOWAIT, curthread); if (error != 0) {