From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5F2C2C33CAF for ; Thu, 16 Jan 2020 18:14:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 39AB12073A for ; Thu, 16 Jan 2020 18:14:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1579198444; bh=UC001LbTVcSUiGfdFhBBYLJYxKzjHeFOJ8dBTV+YjLc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=vw5u1fOF6G1kb4J4ZT9YyuvvSEXly6psAJdu+PrRKttqL/ntGE5/6Mn5Hd22bKCeg WWTaviEjfpjR2dAgOmlOs+RdSLmgvxGlF8z6B6zW75KQZ0pqGrRK5gKXtM1pIK9/IO b2keAK0h0EuIzlNHik5muV/AEY48oLIRlOZubl3k= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2395324AbgAPSOD (ORCPT ); Thu, 16 Jan 2020 13:14:03 -0500 Received: from mail.kernel.org ([198.145.29.99]:49122 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2404891AbgAPRfC (ORCPT ); Thu, 16 Jan 2020 12:35:02 -0500 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 14B88246D8; Thu, 16 Jan 2020 17:35:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1579196101; bh=UC001LbTVcSUiGfdFhBBYLJYxKzjHeFOJ8dBTV+YjLc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=g4ggoxynddU/gcjm3w1S5xD0yI13WBtpTDKVNObbcCHW6gua4vrNlBTLEfPe5ofsm DwmAEmO0XiQXcnln10o6CysD9ePO0bfSt3K4i4WsBdbws3Y23im7G9JXeFWBVFe9Hv vAWa43fhXU8hQ+avCHi0CxfW8v9noqfP4x74C55k= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Lyude Paul , Jerry Zuo , Harry Wentland , Dave Airlie , Sean Paul , Sasha Levin , dri-devel@lists.freedesktop.org Subject: [PATCH AUTOSEL 4.9 012/251] drm/dp_mst: Skip validating ports during destruction, just ref Date: Thu, 16 Jan 2020 12:30:46 -0500 Message-Id: <20200116173445.21385-12-sashal@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200116173445.21385-1-sashal@kernel.org> References: <20200116173445.21385-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Lyude Paul [ Upstream commit c54c7374ff44de5e609506aca7c0deae4703b6d1 ] Jerry Zuo pointed out a rather obscure hotplugging issue that it seems I accidentally introduced into DRM two years ago. Pretend we have a topology like this: |- DP-1: mst_primary |- DP-4: active display |- DP-5: disconnected |- DP-6: active hub |- DP-7: active display |- DP-8: disconnected |- DP-9: disconnected If we unplug DP-6, the topology starting at DP-7 will be destroyed but it's payloads will live on in DP-1's VCPI allocations and thus require removal. However, this removal currently fails because drm_dp_update_payload_part1() will (rightly so) try to validate the port before accessing it, fail then abort. If we keep going, eventually we run the MST hub out of bandwidth and all new allocations will start to fail (or in my case; all new displays just start flickering a ton). We could just teach drm_dp_update_payload_part1() not to drop the port ref in this case, but then we also need to teach drm_dp_destroy_payload_step1() to do the same thing, then hope no one ever adds anything to the that requires a validated port reference in drm_dp_destroy_connector_work(). Kind of sketchy. So let's go with a more clever solution: any port that drm_dp_destroy_connector_work() interacts with is guaranteed to still exist in memory until we say so. While said port might not be valid we don't really care: that's the whole reason we're destroying it in the first place! So, teach drm_dp_get_validated_port_ref() to use the all mighty current_work() function to avoid attempting to validate ports from the context of mgr->destroy_connector_work. I can't see any situation where this wouldn't be safe, and this avoids having to play whack-a-mole in the future of trying to work around port validation. Signed-off-by: Lyude Paul Fixes: 263efde31f97 ("drm/dp/mst: Get validated port ref in drm_dp_update_payload_part1()") Reported-by: Jerry Zuo Cc: Jerry Zuo Cc: Harry Wentland Cc: # v4.6+ Reviewed-by: Dave Airlie Link: https://patchwork.freedesktop.org/patch/msgid/20181113224613.28809-1-lyude@redhat.com Signed-off-by: Sean Paul Signed-off-by: Sasha Levin --- drivers/gpu/drm/drm_dp_mst_topology.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c index e05dda92398c..17aedaaf364c 100644 --- a/drivers/gpu/drm/drm_dp_mst_topology.c +++ b/drivers/gpu/drm/drm_dp_mst_topology.c @@ -980,9 +980,20 @@ static struct drm_dp_mst_port *drm_dp_mst_get_port_ref_locked(struct drm_dp_mst_ static struct drm_dp_mst_port *drm_dp_get_validated_port_ref(struct drm_dp_mst_topology_mgr *mgr, struct drm_dp_mst_port *port) { struct drm_dp_mst_port *rport = NULL; + mutex_lock(&mgr->lock); - if (mgr->mst_primary) - rport = drm_dp_mst_get_port_ref_locked(mgr->mst_primary, port); + /* + * Port may or may not be 'valid' but we don't care about that when + * destroying the port and we are guaranteed that the port pointer + * will be valid until we've finished + */ + if (current_work() == &mgr->destroy_connector_work) { + kref_get(&port->kref); + rport = port; + } else if (mgr->mst_primary) { + rport = drm_dp_mst_get_port_ref_locked(mgr->mst_primary, + port); + } mutex_unlock(&mgr->lock); return rport; } -- 2.20.1