From patchwork Tue Jan 10 15:17:44 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Chris Wilson X-Patchwork-Id: 9507993 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id EA527601E9 for ; Tue, 10 Jan 2017 15:18:01 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id DCD6E28595 for ; Tue, 10 Jan 2017 15:18:01 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id D16702859B; Tue, 10 Jan 2017 15:18:01 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.2 required=2.0 tests=BAYES_00, RCVD_IN_DNSWL_MED autolearn=unavailable version=3.3.1 Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher DHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 898E328595 for ; Tue, 10 Jan 2017 15:18:01 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 0427E6E6CF; Tue, 10 Jan 2017 15:17:56 +0000 (UTC) X-Original-To: dri-devel@lists.freedesktop.org Delivered-To: dri-devel@lists.freedesktop.org Received: from fireflyinternet.com (mail.fireflyinternet.com [109.228.58.192]) by gabe.freedesktop.org (Postfix) with ESMTPS id 894DE6E6CF; Tue, 10 Jan 2017 15:17:53 +0000 (UTC) X-Default-Received-SPF: pass (skip=forwardok (res=PASS)) x-ip-name=78.156.65.138; Received: from nuc-i3427.alporthouse.com (unverified [78.156.65.138]) by fireflyinternet.com (Firefly Internet (M1)) with ESMTP id 4556828-1500050 for multiple; Tue, 10 Jan 2017 15:17:43 +0000 Received: by nuc-i3427.alporthouse.com (sSMTP sendmail emulation); Tue, 10 Jan 2017 15:17:44 +0000 Date: Tue, 10 Jan 2017 15:17:44 +0000 From: Chris Wilson To: Daniel Vetter Subject: Re: [Intel-gfx] [PATCH] drm/probe-helpers: Drop locking from poll_enable Message-ID: <20170110151744.GK5700@nuc-i3427.alporthouse.com> Mail-Followup-To: Chris Wilson , Daniel Vetter , DRI Development , Intel Graphics Development , Daniel Vetter References: <20170110142910.29922-1-daniel.vetter@ffwll.ch> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20170110142910.29922-1-daniel.vetter@ffwll.ch> User-Agent: Mutt/1.5.21 (2010-09-15) Cc: Daniel Vetter , Intel Graphics Development , DRI Development X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" X-Virus-Scanned: ClamAV using ClamSMTP On Tue, Jan 10, 2017 at 03:29:10PM +0100, Daniel Vetter wrote: > It was only needed to protect the connector_list walking, see > > commit 8c4ccc4ab6f64e859d4ff8d7c02c2ed2e956e07f > Author: Daniel Vetter > Date: Thu Jul 9 23:44:26 2015 +0200 > > drm/probe-helper: Grab mode_config.mutex in poll_init/enable > > Unfortunately the commit message of that patch fails to mention that > the new locking check was for the connector_list. > > But that requirement disappeared in > > commit c36a3254f7857f1ad9badbe3578ccc92be541a8e > Author: Daniel Vetter > Date: Thu Dec 15 16:58:43 2016 +0100 > > drm: Convert all helpers to drm_connector_list_iter > > and so we can drop this again. > > This fixes a locking inversion on nouveau, where the rpm code needs to > re-enable. But in other places the rpm_get() calls are nested within > the big modeset locks. > > While at it, also improve the kerneldoc for these two functions a > notch. > > Cc: Dave Airlie > Signed-off-by: Daniel Vetter > --- > drivers/gpu/drm/drm_probe_helper.c | 41 ++++++++++-------------------------- > drivers/gpu/drm/i915/intel_hotplug.c | 4 ++-- > include/drm/drm_crtc_helper.h | 1 - > 3 files changed, 13 insertions(+), 33 deletions(-) > > diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c > index 060211ac74a1..7c70f2a52250 100644 > --- a/drivers/gpu/drm/drm_probe_helper.c > +++ b/drivers/gpu/drm/drm_probe_helper.c > @@ -115,25 +115,24 @@ static int drm_helper_probe_add_cmdline_mode(struct drm_connector *connector) > > #define DRM_OUTPUT_POLL_PERIOD (10*HZ) > /** > - * drm_kms_helper_poll_enable_locked - re-enable output polling. > + * drm_kms_helper_poll_enable - re-enable output polling. > * @dev: drm_device > * > - * This function re-enables the output polling work without > - * locking the mode_config mutex. > + * This function re-enables the output polling work, after it has been > + * temporarily disabled using drm_kms_helper_poll_disable(), for example over > + * suspend/resume. > * > - * This is like drm_kms_helper_poll_enable() however it is to be > - * called from a context where the mode_config mutex is locked > - * already. > + * Drivers can call this helper from their device resume implementation. It is > + * an error to call this when the output polling support has not yet been set > + * up. > */ > -void drm_kms_helper_poll_enable_locked(struct drm_device *dev) > +void drm_kms_helper_poll_enable(struct drm_device *dev) > { > bool poll = false; > struct drm_connector *connector; > struct drm_connector_list_iter conn_iter; > unsigned long delay = DRM_OUTPUT_POLL_PERIOD; > > - WARN_ON(!mutex_is_locked(&dev->mode_config.mutex)); > - > if (!dev->mode_config.poll_enabled || !drm_kms_helper_poll) > return; Hmm, output_poll_execute() itself is not checking this correctly, The connector list is locked, but the other reads are all racy (connector->polled, delayed_event). Those races seem intrinsic and handled by e.g. intel_hotplug.c. Since the locking here was only covering the connector list and that now has its own lock, Reviewed-by: Chris Wilson -Chris diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c index 84b75709af90..cb3febc6e719 100644 --- a/drivers/gpu/drm/drm_probe_helper.c +++ b/drivers/gpu/drm/drm_probe_helper.c @@ -405,7 +405,7 @@ static void output_poll_execute(struct work_struct *work) changed = dev->mode_config.delayed_event; dev->mode_config.delayed_event = false; - if (!drm_kms_helper_poll) + if (!dev->mode_config.poll_enabled || !drm_kms_helper_poll) goto out; if (!mutex_trylock(&dev->mode_config.mutex)) {