From patchwork Tue Oct 21 10:50:26 2014 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Dheeraj Jamwal X-Patchwork-Id: 5117371 Return-Path: X-Original-To: patchwork-ltsi-dev@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork2.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.19.201]) by patchwork2.web.kernel.org (Postfix) with ESMTP id ED359C11AC for ; Tue, 21 Oct 2014 11:33:26 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 0BDB82010F for ; Tue, 21 Oct 2014 11:33:26 +0000 (UTC) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org [140.211.169.12]) (using TLSv1.2 with cipher DHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 28AF320107 for ; Tue, 21 Oct 2014 11:33:25 +0000 (UTC) Received: from mail.linux-foundation.org (localhost [127.0.0.1]) by mail.linuxfoundation.org (Postfix) with ESMTP id A136BEFA; Tue, 21 Oct 2014 11:05:38 +0000 (UTC) X-Original-To: ltsi-dev@lists.linuxfoundation.org Delivered-To: ltsi-dev@mail.linuxfoundation.org Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id 43DD5EDA for ; Tue, 21 Oct 2014 11:05:34 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from mga11.intel.com (mga11.intel.com [192.55.52.93]) by smtp1.linuxfoundation.org (Postfix) with ESMTP id B5CAB1FAB2 for ; Tue, 21 Oct 2014 11:05:32 +0000 (UTC) Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by fmsmga102.fm.intel.com with ESMTP; 21 Oct 2014 04:05:32 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.04,761,1406617200"; d="scan'208";a="617796025" Received: from ubuntu-desktop.png.intel.com ([10.221.122.25]) by fmsmga002.fm.intel.com with ESMTP; 21 Oct 2014 04:05:31 -0700 From: Dheeraj Jamwal To: ltsi-dev@lists.linuxfoundation.org Date: Tue, 21 Oct 2014 18:50:26 +0800 Message-Id: <1413889294-31328-427-git-send-email-dheerajx.s.jamwal@intel.com> X-Mailer: git-send-email 1.7.9.5 In-Reply-To: <1413889294-31328-1-git-send-email-dheerajx.s.jamwal@intel.com> References: <1413889294-31328-1-git-send-email-dheerajx.s.jamwal@intel.com> X-Spam-Status: No, score=-5.6 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_MED, RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org Subject: [LTSI-dev] [PATCH 0426/1094] drm/fb-helper: improve drm_fb_helper_initial_config locking X-BeenThere: ltsi-dev@lists.linuxfoundation.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: "A list to discuss patches, development, and other things related to the LTSI project" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Sender: ltsi-dev-bounces@lists.linuxfoundation.org Errors-To: ltsi-dev-bounces@lists.linuxfoundation.org X-Virus-Scanned: ClamAV using ClamSMTP From: Daniel Vetter The locking in drm_fb_helper_initial_config is a bit troublesome for a few reasons: - We can't just wrap the entire function up into modeset locks since the fbdev registration might call down into fbcon code, which then through our ->set_par implementation needs to be able to grab all modeset locks. So we'd have a neat deadlock. - This implies though that all current callers don't hold any modeset locks by necessity, so we have free reign to grab any modeset locks we need to grab. - The private state of the fbdev helper doesn't need any protection through locks, since once we have the fbdev registered it is mostly invariant or protected through the modeset locking in ->set_par and other callbacks. We can fully rely on driver having non-racy setup sequences here. For the initial config computation we actually may not grab locks since drivers which provide their own magic sauce (like i915) might need to grab locks themselves. - We should grab locks though when we probe outputs. Currently there's not much risk, but already now userspace could start poking at sysfs files and so probe concurrently. I expect that in the future driver init will be much more async, and since probing is really time-consuming this is a prime candidate. - We must not hold any crtc->mutex locks while calling probe functions since those might need to lock a crtc for e.g. load detection. i915 is such a driver. Also it's the probing calls which hit upon piles of new locking asserts I've recently added in commit 62ff94a5492175759546f8bc61383189d6b49122 Author: Daniel Vetter Date: Thu Jan 23 22:18:47 2014 +0100 drm/crtc-helper: remove LOCKING from kerneldoc and commit 63951385052f7974155fa38f962f0f4e9847f90a Author: Daniel Vetter Date: Thu Jan 23 15:14:15 2014 +0100 drm/doc: Repleace LOCKING kerneldoc sections in drm_modes.c Hence the right fix is to grab the mode_config mutex, but only that and only right around the probe calls. It seems to be sufficient to shut up all the locking WARNINGs I see on i915 and nouveau in drm_fb_helper_initial_config. Signed-off-by: Daniel Vetter Tested-by: Thierry Reding Signed-off-by: Dave Airlie (cherry picked from commit 53f1904bced78d7c00f5d874c662ec3ac85d0f9f) Signed-off-by: Dheeraj Jamwal --- drivers/gpu/drm/drm_fb_helper.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c index 060d25a..0a19b02 100644 --- a/drivers/gpu/drm/drm_fb_helper.c +++ b/drivers/gpu/drm/drm_fb_helper.c @@ -1541,9 +1541,11 @@ bool drm_fb_helper_initial_config(struct drm_fb_helper *fb_helper, int bpp_sel) drm_fb_helper_parse_command_line(fb_helper); + mutex_lock(&dev->mode_config.mutex); count = drm_fb_helper_probe_connector_modes(fb_helper, dev->mode_config.max_width, dev->mode_config.max_height); + mutex_unlock(&dev->mode_config.mutex); /* * we shouldn't end up with no modes here. */