From owner-svn-src-all@freebsd.org Thu Nov 1 21:51:43 2018 Return-Path: Delivered-To: svn-src-all@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id E470710DA452; Thu, 1 Nov 2018 21:51:42 +0000 (UTC) (envelope-from imp@FreeBSD.org) Received: from mxrelay.nyi.freebsd.org (mxrelay.nyi.freebsd.org [IPv6:2610:1c1:1:606c::19:3]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client CN "mxrelay.nyi.freebsd.org", Issuer "Let's Encrypt Authority X3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 94D8B8E183; Thu, 1 Nov 2018 21:51:42 +0000 (UTC) (envelope-from imp@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 mxrelay.nyi.freebsd.org (Postfix) with ESMTPS id 74D352192A; Thu, 1 Nov 2018 21:51:42 +0000 (UTC) (envelope-from imp@FreeBSD.org) Received: from repo.freebsd.org ([127.0.1.37]) by repo.freebsd.org (8.15.2/8.15.2) with ESMTP id wA1LpgWG019846; Thu, 1 Nov 2018 21:51:42 GMT (envelope-from imp@FreeBSD.org) Received: (from imp@localhost) by repo.freebsd.org (8.15.2/8.15.2/Submit) id wA1Lpgtj019844; Thu, 1 Nov 2018 21:51:42 GMT (envelope-from imp@FreeBSD.org) Message-Id: <201811012151.wA1Lpgtj019844@repo.freebsd.org> X-Authentication-Warning: repo.freebsd.org: imp set sender to imp@FreeBSD.org using -f From: Warner Losh Date: Thu, 1 Nov 2018 21:51:42 +0000 (UTC) To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r340024 - in head/sys/cam: . scsi X-SVN-Group: head X-SVN-Commit-Author: imp X-SVN-Commit-Paths: in head/sys/cam: . scsi X-SVN-Commit-Revision: 340024 X-SVN-Commit-Repository: base 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: 2.1.29 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, 01 Nov 2018 21:51:43 -0000 Author: imp Date: Thu Nov 1 21:51:41 2018 New Revision: 340024 URL: https://svnweb.freebsd.org/changeset/base/340024 Log: Add comments explaining what hold/unhold do They act as a simple one-deep semaphore to keep open/close/probe from running at the same time to avoid races that creates. Modified: head/sys/cam/cam_periph.c head/sys/cam/scsi/scsi_da.c Modified: head/sys/cam/cam_periph.c ============================================================================== --- head/sys/cam/cam_periph.c Thu Nov 1 21:49:49 2018 (r340023) +++ head/sys/cam/cam_periph.c Thu Nov 1 21:51:41 2018 (r340024) @@ -470,6 +470,12 @@ cam_periph_release(struct cam_periph *periph) mtx_unlock(mtx); } +/* + * hold/unhold act as mutual exclusion for sections of the code that + * need to sleep and want to make sure that other sections that + * will interfere are held off. This only protects exclusive sections + * from each other. + */ int cam_periph_hold(struct cam_periph *periph, int priority) { Modified: head/sys/cam/scsi/scsi_da.c ============================================================================== --- head/sys/cam/scsi/scsi_da.c Thu Nov 1 21:49:49 2018 (r340023) +++ head/sys/cam/scsi/scsi_da.c Thu Nov 1 21:51:41 2018 (r340024) @@ -2697,9 +2697,10 @@ daregister(struct cam_periph *periph, void *arg) TASK_INIT(&softc->sysctl_task, 0, dasysctlinit, periph); /* - * Take an exclusive refcount on the periph while dastart is called - * to finish the probe. The reference will be dropped in dadone at - * the end of probe. + * Take an exclusive section lock qon the periph while dastart is called + * to finish the probe. The lock will be dropped in dadone at the end + * of probe. This locks out daopen and daclose from racing with the + * probe. * * XXX if cam_periph_hold returns an error, we don't hold a refcount. */