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 3BA15C433F5 for ; Thu, 17 Feb 2022 16:08:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233863AbiBQQJL (ORCPT ); Thu, 17 Feb 2022 11:09:11 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:50344 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233312AbiBQQJK (ORCPT ); Thu, 17 Feb 2022 11:09:10 -0500 Received: from mail-pl1-x634.google.com (mail-pl1-x634.google.com [IPv6:2607:f8b0:4864:20::634]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A0FA7178BD7 for ; Thu, 17 Feb 2022 08:08:55 -0800 (PST) Received: by mail-pl1-x634.google.com with SMTP id 10so4976695plj.1 for ; Thu, 17 Feb 2022 08:08:55 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=VD8H9XEccLJ1gEJ8HFd5QAYd/aMwLkrTq6BJhjDSisU=; b=F2rnoQOUj5vrdaK05HWLiQ7Dayy2FS/VLwwppCjteGUtmVGphPSPL1yNlR/PsVhO4Q SGeRoVRv5Uus+p4dn8QbXAGf80LP4h24IJAa0YKQc/bBrJA2mgvX6k6S+QaZhSinsQPe o216cTDDHjXReLeUyM4oLkcXFtL1l/32drgLI8Q3Ol851JV0AFiUSkZYV96ZmH6yoaRz AKOTAqvSoj03fN1c6IOu25o9+GmlKYmh8Tz/z/Z1zg3CfaJqHt1e0AWkINesw/Pf2V0l g76JZRFDHXvhz1CCgn1/99do97O3lEyvZTQa1XyJAFrLSbwg3bv9oVKn+Ugr30Tfha1B 919w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=VD8H9XEccLJ1gEJ8HFd5QAYd/aMwLkrTq6BJhjDSisU=; b=Xd+SlpQ78fktUmibca/RrAm73bu6WK0xnNNy487RTR51agwwVlfsoEbBY7p9nw/2OB oCqx4Qq4HwjrCYRppiTRewVvqXgl4EKzasAFPEdh7RbTQHsgLddS6yo5DwEtpd6+b86Q Pzmzn6K6bYgxi5zx6+O3p5T9/lTDzEYD95wX7XPyX4NeoYvJurbGkxv6AkeL+fnpTA25 BUS6rz0HcWOM8gG/VAv5RH0EgqOnjZOaRHp4xIAlvYB3y7apAIEad2nhgJlPDGB8vHa3 v0llBbsgihmmx27HKJJ9wvSd17VG77hcbUW6PJcPLO5ztBpYgbAwCVIZOlaKYVPszvE/ Ypqw== X-Gm-Message-State: AOAM530iCRboKEcjcWmdO2vvIiGSMk8vbz0C8uWexYQX+vUcbaHjboK0 ntK/Pt4vaEfUZQAviuXTST6RBg== X-Google-Smtp-Source: ABdhPJyFsjmnJxcyI3zQL+VFCRE3os2dZrHdxY5v38ChREUHcE+PvGbETp2COJG44FjB8IEmuf5tZQ== X-Received: by 2002:a17:90a:4dc7:b0:1b9:ca2:311e with SMTP id r7-20020a17090a4dc700b001b90ca2311emr3717927pjl.175.1645114135171; Thu, 17 Feb 2022 08:08:55 -0800 (PST) Received: from p14s (S0106889e681aac74.cg.shawcable.net. [68.147.0.187]) by smtp.gmail.com with ESMTPSA id h9sm51611pfv.135.2022.02.17.08.08.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 17 Feb 2022 08:08:53 -0800 (PST) Date: Thu, 17 Feb 2022 09:08:51 -0700 From: Mathieu Poirier To: AngeloGioacchino Del Regno Cc: bjorn.andersson@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 Subject: Re: [PATCH] rpmsg: mtk_rpmsg: Fix circular locking dependency Message-ID: <20220217160851.GA474184@p14s> References: <20220114144737.375621-1-angelogioacchino.delregno@collabora.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-remoteproc@vger.kernel.org On Wed, Feb 16, 2022 at 05:06:22PM +0100, AngeloGioacchino Del Regno wrote: > 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... :) > This seems to have slipped through the cracks... I will take a look later today. Thanks, Mathieu > > --- > > 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; > > 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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 9279CC433EF for ; Thu, 17 Feb 2022 16:09:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=/OD9Km+zboq5ODflFkzAYjRCo03rTU683FTbo5t9b30=; b=4ggC53qB8QaUrB 7+ha5To3PABq5HyHet4n5ZUHlS6WBz39zbV3dUUqvwjitGqU26M9FtVPBx7i7laV7NLiWIzfM6doA 4I5FK1ulkcEU5EY5L2dyXu42z5AuQAHDUEKh4SVVj25AyntOI42ap4z7d/T+Uvc+bS+4HrmEuO/QN v3WSwxUe/txXF3KyYpbLrl+2GP2xBN24Yfe1FgyxFvhoNuM0qF9H4jtkSG5su6/XNOLrMSE5SJrUw IetxL9I7VMEP+hyfNg7QuRtPw2fihQS3nmk1AcXlWvywzJeQGxtDcrM/dDdlwf+4y2YoKOYUkQLN+ ++uKM4kGVJlsD0PoJT7g==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1nKjLB-00BO5Y-RA; Thu, 17 Feb 2022 16:09:09 +0000 Received: from mail-pj1-x102c.google.com ([2607:f8b0:4864:20::102c]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1nKjKy-00BO1o-VT for linux-mediatek@lists.infradead.org; Thu, 17 Feb 2022 16:08:58 +0000 Received: by mail-pj1-x102c.google.com with SMTP id b8so6005461pjb.4 for ; Thu, 17 Feb 2022 08:08:55 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=VD8H9XEccLJ1gEJ8HFd5QAYd/aMwLkrTq6BJhjDSisU=; b=F2rnoQOUj5vrdaK05HWLiQ7Dayy2FS/VLwwppCjteGUtmVGphPSPL1yNlR/PsVhO4Q SGeRoVRv5Uus+p4dn8QbXAGf80LP4h24IJAa0YKQc/bBrJA2mgvX6k6S+QaZhSinsQPe o216cTDDHjXReLeUyM4oLkcXFtL1l/32drgLI8Q3Ol851JV0AFiUSkZYV96ZmH6yoaRz AKOTAqvSoj03fN1c6IOu25o9+GmlKYmh8Tz/z/Z1zg3CfaJqHt1e0AWkINesw/Pf2V0l g76JZRFDHXvhz1CCgn1/99do97O3lEyvZTQa1XyJAFrLSbwg3bv9oVKn+Ugr30Tfha1B 919w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=VD8H9XEccLJ1gEJ8HFd5QAYd/aMwLkrTq6BJhjDSisU=; b=5BFq0jTze7c0S3+JVLcUZFFzPLAnCCpo5olTWznWMiMVGu4eNYRNC3KGyya1GeuAxb SWB6ZAy76bFytbuzv54lFME2aob72XbnIM5dqloiIYuuM7QzK18sYoZ9o4Q5dJecEq0S COyMet6NvRblFq98ugA9ISDdXMmW9mEzehFyE940PIzQL1CgWonyk+ppuZRVQ1UPILUL hfHg9wzrHAYBtyQQVpsrB6ECxW3nD5BRA0vPruqKBOg9Thv/Y3TpboEz2kGaCQHPiuzi GM+Bp6lUIw7r/sJudTt2TCsXXTVgSLw22+JOdLb6TpxgbZ5EuMYoBMdWEJXnkutxZDtI 6RZg== X-Gm-Message-State: AOAM533ewH43kukmmETzIicG7vFHVjhm0lhGhfgCpU4Zor6VFz1/ljXQ 4QfLP822i9BH9HVTmKySNuKdWg== X-Google-Smtp-Source: ABdhPJyFsjmnJxcyI3zQL+VFCRE3os2dZrHdxY5v38ChREUHcE+PvGbETp2COJG44FjB8IEmuf5tZQ== X-Received: by 2002:a17:90a:4dc7:b0:1b9:ca2:311e with SMTP id r7-20020a17090a4dc700b001b90ca2311emr3717927pjl.175.1645114135171; Thu, 17 Feb 2022 08:08:55 -0800 (PST) Received: from p14s (S0106889e681aac74.cg.shawcable.net. [68.147.0.187]) by smtp.gmail.com with ESMTPSA id h9sm51611pfv.135.2022.02.17.08.08.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 17 Feb 2022 08:08:53 -0800 (PST) Date: Thu, 17 Feb 2022 09:08:51 -0700 From: Mathieu Poirier To: AngeloGioacchino Del Regno Cc: bjorn.andersson@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 Subject: Re: [PATCH] rpmsg: mtk_rpmsg: Fix circular locking dependency Message-ID: <20220217160851.GA474184@p14s> References: <20220114144737.375621-1-angelogioacchino.delregno@collabora.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220217_080857_029934_9895F312 X-CRM114-Status: GOOD ( 22.48 ) X-BeenThere: linux-mediatek@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "Linux-mediatek" Errors-To: linux-mediatek-bounces+linux-mediatek=archiver.kernel.org@lists.infradead.org On Wed, Feb 16, 2022 at 05:06:22PM +0100, AngeloGioacchino Del Regno wrote: > 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... :) > This seems to have slipped through the cracks... I will take a look later today. Thanks, Mathieu > > --- > > 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; > > _______________________________________________ Linux-mediatek mailing list Linux-mediatek@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-mediatek 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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 80CEEC433EF for ; Thu, 17 Feb 2022 16:10:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=cOGG9qvlqrVrdGa7L4vaLFPsetauftN5lo0zRdS5jHY=; b=kn+bHxfuB2327A n87tY950UxywuFrHX813oThs7IyOXW7VQNLc9iTlV6AsC6Z8ocoV515gcAlr2wugiP+JH/lxM3vd4 iA7naW/w/Bp7C8JGtRTqKWOofraWoBUjpPB9fK8Ki1ciiyCX8pQWUJWtW6Z4yNZSjAsx4dHERXoVs rED1yz+BSOBOIPFnMy01QG+nsPHVmvEnTdGFLkUJo8Fc5oY1d3PNU046l5omiHDr9NegW3Vc3jDth p3+tTfGrAztkTt0FnKttpZgq56s7mHjtEWrObr/XdD4SDRSbFCeBb6bFp+qEdFT97W5rOAYbGlhis JfEtJZhjMoD7CoWI2QuA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1nKjL2-00BO31-LF; Thu, 17 Feb 2022 16:09:00 +0000 Received: from mail-pj1-x1029.google.com ([2607:f8b0:4864:20::1029]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1nKjKy-00BO1l-Tz for linux-arm-kernel@lists.infradead.org; Thu, 17 Feb 2022 16:08:58 +0000 Received: by mail-pj1-x1029.google.com with SMTP id om7so5997072pjb.5 for ; Thu, 17 Feb 2022 08:08:55 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=VD8H9XEccLJ1gEJ8HFd5QAYd/aMwLkrTq6BJhjDSisU=; b=F2rnoQOUj5vrdaK05HWLiQ7Dayy2FS/VLwwppCjteGUtmVGphPSPL1yNlR/PsVhO4Q SGeRoVRv5Uus+p4dn8QbXAGf80LP4h24IJAa0YKQc/bBrJA2mgvX6k6S+QaZhSinsQPe o216cTDDHjXReLeUyM4oLkcXFtL1l/32drgLI8Q3Ol851JV0AFiUSkZYV96ZmH6yoaRz AKOTAqvSoj03fN1c6IOu25o9+GmlKYmh8Tz/z/Z1zg3CfaJqHt1e0AWkINesw/Pf2V0l g76JZRFDHXvhz1CCgn1/99do97O3lEyvZTQa1XyJAFrLSbwg3bv9oVKn+Ugr30Tfha1B 919w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=VD8H9XEccLJ1gEJ8HFd5QAYd/aMwLkrTq6BJhjDSisU=; b=aF0MostCL4famp22YxVe2iM2T7JVB+9GNtn6LltRPWOti9ER4kVAyDJM+IRYYSWXKN sA/rz1+0U+b1CY/Cc7jiYrJdbslkvzEWjaDwtWc2AsyeVb5+6ZRu9bDvdSSuK8JJWbwQ SN1W0ZpYF3OYxlF5QILf/5RszmY5RX4a9MZ8l6pfsa0rQPdOoj7cJQ8uyqE8fUVbS0cc 6j6Myv0nu/Ft6n+nnCmj2yPEUZGjbuwEBVNaCp/DSKTxmhBt56npuor4tIoizcQxjaV2 +5uFJLdSLQ3PIsaAQw3k//0y9sw8SxyZmNiwuK4BYecOOUteO/g3Cb9II0ZCrpSc6RAc bmWA== X-Gm-Message-State: AOAM530pqqKYk5VSkw2D1FOz0Zc3qqHKWDXTRFI//hXWhGpKtX6J3rkm luFRQpY+qrrlAQFkApsArxRTRg== X-Google-Smtp-Source: ABdhPJyFsjmnJxcyI3zQL+VFCRE3os2dZrHdxY5v38ChREUHcE+PvGbETp2COJG44FjB8IEmuf5tZQ== X-Received: by 2002:a17:90a:4dc7:b0:1b9:ca2:311e with SMTP id r7-20020a17090a4dc700b001b90ca2311emr3717927pjl.175.1645114135171; Thu, 17 Feb 2022 08:08:55 -0800 (PST) Received: from p14s (S0106889e681aac74.cg.shawcable.net. [68.147.0.187]) by smtp.gmail.com with ESMTPSA id h9sm51611pfv.135.2022.02.17.08.08.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 17 Feb 2022 08:08:53 -0800 (PST) Date: Thu, 17 Feb 2022 09:08:51 -0700 From: Mathieu Poirier To: AngeloGioacchino Del Regno Cc: bjorn.andersson@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 Subject: Re: [PATCH] rpmsg: mtk_rpmsg: Fix circular locking dependency Message-ID: <20220217160851.GA474184@p14s> References: <20220114144737.375621-1-angelogioacchino.delregno@collabora.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220217_080856_996581_4F6B10F2 X-CRM114-Status: GOOD ( 23.54 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Feb 16, 2022 at 05:06:22PM +0100, AngeloGioacchino Del Regno wrote: > 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... :) > This seems to have slipped through the cracks... I will take a look later today. Thanks, Mathieu > > --- > > 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; > > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel