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 4BE37C10DAA for ; Thu, 30 Nov 2023 05:32:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344505AbjK3FcF (ORCPT ); Thu, 30 Nov 2023 00:32:05 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46240 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234948AbjK3FcA (ORCPT ); Thu, 30 Nov 2023 00:32:00 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5BAF8D7F for ; Wed, 29 Nov 2023 21:32:05 -0800 (PST) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 151AFC433C7; Thu, 30 Nov 2023 05:32:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1701322325; bh=pMAZRD6C2KxJP4HEAtpAIDxbTaSlvGsc71rh/SQWRtU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=nzCN1zJVSMh+g5X7qRKecWziuXOdWr00FRIYi06EW39LWAwKZx05wqoCY3qOBN+FI rQUnlYiDyKD9a22jXTQtSUBuGXxEmyuBWzZTFv+e7jwBPyI5Qe1Nrk+/o1WVjpL4uX pmPh7lSAAQ80/hn/AhNV9ezx+cZYrnDeAh0ifTa6npt+0Ka6SDakf5SBrKTYnTC7u5 YPfn6eRwh4GVevufSN/gXUaw3bIBXFcoNWM2tBonHNxnmVUJiqKUl1A5IQTD9COAEL 3NPPQDKNiWlINy8sljZrtPDqJG7/3ulyf92erDT42KHQbXFlD06+WWiS7ACC3gp76r T/x+mREHM8E3Q== Date: Thu, 30 Nov 2023 11:01:57 +0530 From: Manivannan Sadhasivam To: Qiang Yu Cc: Manivannan Sadhasivam , 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: <20231130053157.GB3043@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> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <5eb0a521-0b72-4d15-9a65-429c4c123833@quicinc.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 > > > > 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