From nobody Sun Sep 22 09:20:44 2024 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 88D80C433F5 for ; Fri, 14 Jan 2022 14:47:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242021AbiANOrx (ORCPT ); Fri, 14 Jan 2022 09:47:53 -0500 Received: from bhuna.collabora.co.uk ([46.235.227.227]:58570 "EHLO bhuna.collabora.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241999AbiANOrt (ORCPT ); Fri, 14 Jan 2022 09:47:49 -0500 Received: from [127.0.0.1] (localhost [127.0.0.1]) (Authenticated sender: kholk11) with ESMTPSA id A6C881F46A72 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1642171668; bh=cTHqww4IZbi5PdxScVJ5RmgEFWGNWZU4AMAqnvnN1vM=; h=From:To:Cc:Subject:Date:From; b=D8AJQ4G4r14QCgGUpRCWn6AKwg2pAfphNZFKn9dWfT35vWJoI66KVSW7wOn/gXH8F 8+A7uBI3Sn2tDAHAu12zTel7evWbULUfMEnbsbcxcD7qYOmoOwRj5QuEa6f11pCGRl 5TKGmqC9UO3H/KHxP4s6DO9sC+IGFySuqpp0mit5cnsdk9mYk37bFOnzi4dGPnKHZv ANmplostgKQQYVTggvCRI3XtxFzRbJFVi+xojzgODipky/Se7m9u57A3wmx0z3RvM+ VgAMkZairRwIwTkLmvYFbS+bM97KSZJjTomHxGawqHkf0W88KMMwmKbb8P1u8d1H3U 7bYait9ekDf5w== From: AngeloGioacchino Del Regno To: bjorn.andersson@linaro.org Cc: mathieu.poirier@linaro.org, matthias.bgg@gmail.com, pihsun@chromium.org, linux-remoteproc@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org, linux-kernel@vger.kernel.org, kernel@collabora.com, AngeloGioacchino Del Regno Subject: [PATCH] rpmsg: mtk_rpmsg: Fix circular locking dependency Date: Fri, 14 Jan 2022 15:47:37 +0100 Message-Id: <20220114144737.375621-1-angelogioacchino.delregno@collabora.com> X-Mailer: git-send-email 2.33.1 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" During execution of the worker that's used to register rpmsg devices we are safely locking the channels mutex but, when creating a new endpoint for such devices, we are registering a IPI on the SCP, which then makes the SCP to trigger an interrupt, lock its own mutex and in turn register more subdevices. This creates a circular locking dependency situation, as the mtk_rpmsg channels_lock will then depend on the SCP IPI lock. [ 18.014514] Possible unsafe locking scenario: [ 18.014515] CPU0 CPU1 [ 18.014517] ---- ---- [ 18.045467] lock(&mtk_subdev->channels_lock); [ 18.045474] lock(&scp->ipi_desc[i].lock); [ 18.228399] lock(&mtk_subdev->channels_lo= ck); [ 18.228405] lock(&scp->ipi_desc[i].lock); [ 18.264405] To solve this, simply unlock the channels_lock mutex before calling mtk_rpmsg_register_device() and relock it right after, as safety is still ensured by the locking mechanism that happens right after through SCP. Notably, mtk_rpmsg_register_device() does not even require locking. Fixes: 7017996951fd ("rpmsg: add rpmsg support for mt8183 SCP.") Signed-off-by: AngeloGioacchino Del Regno --- drivers/rpmsg/mtk_rpmsg.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/drivers/rpmsg/mtk_rpmsg.c b/drivers/rpmsg/mtk_rpmsg.c index 5b4404b8be4c..d1213c33da20 100644 --- a/drivers/rpmsg/mtk_rpmsg.c +++ b/drivers/rpmsg/mtk_rpmsg.c @@ -234,7 +234,9 @@ static void mtk_register_device_work_function(struct wo= rk_struct *register_work) if (info->registered) continue; =20 + mutex_unlock(&subdev->channels_lock); ret =3D mtk_rpmsg_register_device(subdev, &info->info); + mutex_lock(&subdev->channels_lock); if (ret) { dev_err(&pdev->dev, "Can't create rpmsg_device\n"); continue; --=20 2.33.1