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[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-kernel@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; > >