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 D268BC10DC1 for ; Wed, 6 Dec 2023 13:48:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1378606AbjLFNst (ORCPT ); Wed, 6 Dec 2023 08:48:49 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33956 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1378499AbjLFNst (ORCPT ); Wed, 6 Dec 2023 08:48:49 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 790C312B for ; Wed, 6 Dec 2023 05:48:55 -0800 (PST) Received: by smtp.kernel.org (Postfix) with ESMTPSA id A45E9C433C8; Wed, 6 Dec 2023 13:48:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1701870535; bh=tkjYySP7sGQTDkykz5DyN5SpU1SCRDQmOXY6lWHCTck=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=ZszqivOowVXi23GOrtIS3SaJLBK5ZushL2trGqtbqmx/01RHzero59mm12WHqMJiU aShR82QKQs2aC/Dy8BoyugJ/UkRKJi8GqY1Txbi1phowxKb0sN3ugu5USYcGYiPiEX LzY8azOf4tXJRrkydxtWGgZDpaogM0aJo47krLsSPJw6ScT15u78eRulMW+NCWlIHg 249LIFckXYdv7voqbA/0EaPXVnZj95NfVgm5jFw+ijV2RIdR/cM+7WFMU9pzFUmCWF ofUvVjIhVl7m5wcinZMGWGkyMfy+KYjK8nhzOMixVpCz9KMiEdB6JadeulCaE0r1lY 2v6FvvWWh8DcA== Date: Wed, 6 Dec 2023 19:18:48 +0530 From: Manivannan Sadhasivam To: Qiang Yu Cc: quic_jhugo@quicinc.com, mhi@lists.linux.dev, linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org, quic_cang@quicinc.com, quic_mrana@quicinc.com Subject: Re: [PATCH v4 2/4] bus: mhi: host: Drop chan lock before queuing buffers Message-ID: <20231206134848.GG12802@thinkpad> References: <1699939661-7385-1-git-send-email-quic_qianyu@quicinc.com> <1699939661-7385-3-git-send-email-quic_qianyu@quicinc.com> <20231124100403.GA4536@thinkpad> <639d6008-bdfa-4b6e-b622-e916003ec908@quicinc.com> <20231128133252.GX3088@thinkpad> <5eb0a521-0b72-4d15-9a65-429c4c123833@quicinc.com> <20231130053157.GB3043@thinkpad> <9873ee7b-7ef1-4327-8e22-49e1cd3872f1@quicinc.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <9873ee7b-7ef1-4327-8e22-49e1cd3872f1@quicinc.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Dec 06, 2023 at 10:25:12AM +0800, Qiang Yu wrote: > > On 11/30/2023 1:31 PM, Manivannan Sadhasivam wrote: > > On Wed, Nov 29, 2023 at 11:29:07AM +0800, Qiang Yu wrote: > > > On 11/28/2023 9:32 PM, Manivannan Sadhasivam wrote: > > > > On Mon, Nov 27, 2023 at 03:13:55PM +0800, Qiang Yu wrote: > > > > > On 11/24/2023 6:04 PM, Manivannan Sadhasivam wrote: > > > > > > On Tue, Nov 14, 2023 at 01:27:39PM +0800, Qiang Yu wrote: > > > > > > > Ensure read and write locks for the channel are not taken in succession by > > > > > > > dropping the read lock from parse_xfer_event() such that a callback given > > > > > > > to client can potentially queue buffers and acquire the write lock in that > > > > > > > process. Any queueing of buffers should be done without channel read lock > > > > > > > acquired as it can result in multiple locks and a soft lockup. > > > > > > > > > > > > > Is this patch trying to fix an existing issue in client drivers or a potential > > > > > > issue in the future drivers? > > > > > > > > > > > > Even if you take care of disabled channels, "mhi_event->lock" acquired during > > > > > > mhi_mark_stale_events() can cause deadlock, since event lock is already held by > > > > > > mhi_ev_task(). > > > > > > > > > > > > I'd prefer not to open the window unless this patch is fixing a real issue. > > > > > > > > > > > > - Mani > > > > > In [PATCH v4 1/4] bus: mhi: host: Add spinlock to protect WP access when > > > > > queueing > > > > > TREs,  we add > > > > > write_lock_bh(&mhi_chan->lock)/write_unlock_bh(&mhi_chan->lock) > > > > > in mhi_gen_tre, which may be invoked as part of mhi_queue in client xfer > > > > > callback, > > > > > so we have to use read_unlock_bh(&mhi_chan->lock) here to avoid acquiring > > > > > mhi_chan->lock > > > > > twice. > > > > > > > > > > Sorry for confusing you. Do you think we need to sqush this two patch into > > > > > one? > > > > Well, if patch 1 is introducing a potential deadlock, then we should fix patch > > > > 1 itself and not introduce a follow up patch. > > > > > > > > But there is one more issue that I pointed out in my previous reply. > > > Sorry, I can not understand why "mhi_event->lock" acquired during > > > mhi_mark_stale_events() can cause deadlock. In mhi_ev_task(), we will > > > not invoke mhi_mark_stale_events(). Can you provide some interpretation? > > Going by your theory that if a channel gets disabled while processing the event, > > the process trying to disable the channel will try to acquire "mhi_event->lock" > > which is already held by the process processing the event. > > > > - Mani > OK, I get you. Thank you for kind explanation. Hopefully I didn't intrude > too much. Not at all. Btw, did you actually encounter any issue that this patch is trying to fix? Or just fixing based on code inspection. - Mani > > > > > > Also, I'm planning to cleanup the locking mess within MHI in the coming days. > > > > Perhaps we can revisit this series at that point of time. Will that be OK for > > > > you? > > > Sure, that will be great. > > > > - Mani > > > > > > > > > > > Signed-off-by: Qiang Yu > > > > > > > --- > > > > > > > drivers/bus/mhi/host/main.c | 4 ++++ > > > > > > > 1 file changed, 4 insertions(+) > > > > > > > > > > > > > > diff --git a/drivers/bus/mhi/host/main.c b/drivers/bus/mhi/host/main.c > > > > > > > index 6c6d253..c4215b0 100644 > > > > > > > --- a/drivers/bus/mhi/host/main.c > > > > > > > +++ b/drivers/bus/mhi/host/main.c > > > > > > > @@ -642,6 +642,8 @@ static int parse_xfer_event(struct mhi_controller *mhi_cntrl, > > > > > > > mhi_del_ring_element(mhi_cntrl, tre_ring); > > > > > > > local_rp = tre_ring->rp; > > > > > > > + read_unlock_bh(&mhi_chan->lock); > > > > > > > + > > > > > > > /* notify client */ > > > > > > > mhi_chan->xfer_cb(mhi_chan->mhi_dev, &result); > > > > > > > @@ -667,6 +669,8 @@ static int parse_xfer_event(struct mhi_controller *mhi_cntrl, > > > > > > > kfree(buf_info->cb_buf); > > > > > > > } > > > > > > > } > > > > > > > + > > > > > > > + read_lock_bh(&mhi_chan->lock); > > > > > > > } > > > > > > > break; > > > > > > > } /* CC_EOT */ > > > > > > > -- > > > > > > > 2.7.4 > > > > > > > > > > > > > > -- மணிவண்ணன் சதாசிவம்