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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 689DCC433F5 for ; Wed, 16 Feb 2022 16:06:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233907AbiBPQGo (ORCPT ); Wed, 16 Feb 2022 11:06:44 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:60006 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235944AbiBPQGn (ORCPT ); Wed, 16 Feb 2022 11:06:43 -0500 Received: from bhuna.collabora.co.uk (bhuna.collabora.co.uk [46.235.227.227]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 939024925A; Wed, 16 Feb 2022 08:06:27 -0800 (PST) Received: from [127.0.0.1] (localhost [127.0.0.1]) (Authenticated sender: kholk11) with ESMTPSA id A46EF1F450A4 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1645027586; bh=aefrMXzupsLGu5Ex9arbBV1OgQCjmS+CBwjP8HtAD84=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=cqo4f+MCDMkcgOCnLgpDF2cDT0hDDpHza/7IDHJhLT5XOWGpgB/i9ooaOOmglHiE0 WaErsHsIw1PiM+OynCDAdzSo2fYKAvgRhAS+sb6RUiaoGMrtKktkH6mWP1Tr56h4qG GdzKJPC8yN7m49uYqOCrJAlNkXWcZVIPe6zPk/SYqv5qyK0OxaDfPmeTwINA8c+cZV 221lkdkjEwWk2dMlc/XpBKJulMep5vaFWrVu0HlvpCY2Ag3bu/s9XQtcxi3mQGtU9K 4dwcRMqLI2pLQNXphjzNhsOUfG77I/4QiHZukTz3u5qJv59xvdEiS5GBYYxkrPuIIE YwjpvwvjGFLuQ== Message-ID: Date: Wed, 16 Feb 2022 17:06:22 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.5.1 Subject: Re: [PATCH] rpmsg: mtk_rpmsg: Fix circular locking dependency Content-Language: en-US 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 References: <20220114144737.375621-1-angelogioacchino.delregno@collabora.com> From: AngeloGioacchino Del Regno In-Reply-To: <20220114144737.375621-1-angelogioacchino.delregno@collabora.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-remoteproc@vger.kernel.org Il 14/01/22 15:47, AngeloGioacchino Del Regno ha scritto: > 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_lock); > [ 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 Friendly ping for an important fix... :) > --- > 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 work_struct *register_work) > if (info->registered) > continue; > > + mutex_unlock(&subdev->channels_lock); > ret = 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;