From owner-svn-src-all@FreeBSD.ORG Sun Jul 6 22:56:35 2014 Return-Path: Delivered-To: svn-src-all@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 4C900B58; Sun, 6 Jul 2014 22:56:35 +0000 (UTC) Received: from svn.freebsd.org (svn.freebsd.org [IPv6:2001:1900:2254:2068::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 396902DCB; Sun, 6 Jul 2014 22:56:35 +0000 (UTC) Received: from svn.freebsd.org ([127.0.1.70]) by svn.freebsd.org (8.14.8/8.14.8) with ESMTP id s66MuZlV073324; Sun, 6 Jul 2014 22:56:35 GMT (envelope-from mjg@svn.freebsd.org) Received: (from mjg@localhost) by svn.freebsd.org (8.14.8/8.14.8/Submit) id s66MuZ2F073323; Sun, 6 Jul 2014 22:56:35 GMT (envelope-from mjg@svn.freebsd.org) Message-Id: <201407062256.s66MuZ2F073323@svn.freebsd.org> From: Mateusz Guzik Date: Sun, 6 Jul 2014 22:56:35 +0000 (UTC) To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-10@freebsd.org Subject: svn commit: r268339 - stable/10/sys/kern X-SVN-Group: stable-10 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: 2.1.18 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: Sun, 06 Jul 2014 22:56:35 -0000 Author: mjg Date: Sun Jul 6 22:56:34 2014 New Revision: 268339 URL: http://svnweb.freebsd.org/changeset/base/268339 Log: MFC r267755: Don't take filedesc lock in fdunshare(). We can read refcnt safely and only care if it is equal to 1. If it could suddenly change from 1 to something bigger the code would be buggy even in the previous form and transitions from > 1 to 1 are equally racy and harmless (we copy even though there is no need). Modified: stable/10/sys/kern/kern_descrip.c Modified: stable/10/sys/kern/kern_descrip.c ============================================================================== --- stable/10/sys/kern/kern_descrip.c Sun Jul 6 22:54:17 2014 (r268338) +++ stable/10/sys/kern/kern_descrip.c Sun Jul 6 22:56:34 2014 (r268339) @@ -1885,17 +1885,14 @@ fdshare(struct filedesc *fdp) void fdunshare(struct proc *p, struct thread *td) { + struct filedesc *tmp; - FILEDESC_XLOCK(p->p_fd); - if (p->p_fd->fd_refcnt > 1) { - struct filedesc *tmp; - - FILEDESC_XUNLOCK(p->p_fd); - tmp = fdcopy(p->p_fd); - fdescfree(td); - p->p_fd = tmp; - } else - FILEDESC_XUNLOCK(p->p_fd); + if (p->p_fd->fd_refcnt == 1) + return; + + tmp = fdcopy(p->p_fd); + fdescfree(td); + p->p_fd = tmp; } /*