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 X-Spam-Level: X-Spam-Status: No, score=-11.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 53A96C433E7 for ; Fri, 16 Oct 2020 11:47:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EBA292084C for ; Fri, 16 Oct 2020 11:47:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2406887AbgJPLrb (ORCPT ); Fri, 16 Oct 2020 07:47:31 -0400 Received: from foss.arm.com ([217.140.110.172]:35490 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2406879AbgJPLrb (ORCPT ); Fri, 16 Oct 2020 07:47:31 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id EE7FBD6E; Fri, 16 Oct 2020 04:47:30 -0700 (PDT) Received: from bogus (unknown [10.57.17.164]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B37B23F66B; Fri, 16 Oct 2020 04:47:29 -0700 (PDT) Date: Fri, 16 Oct 2020 12:47:27 +0100 From: Sudeep Holla To: Jerome Brunet Cc: Ionela Voinescu , Jassi Brar , Kevin Hilman , linux-amlogic@lists.infradead.org, Da Xue , linux-kernel@vger.kernel.org Subject: Re: [PATCH] mailbox: cancel timer before starting it Message-ID: <20201016114727.kvjimgaubcrcmp2k@bogus> References: <20200923123916.1115962-1-jbrunet@baylibre.com> <20201015134628.GA11989@arm.com> <1jlfg7k2ux.fsf@starbuckisacylon.baylibre.com> <20201015142935.GA12516@arm.com> <20201016084428.gthqj25wrvnqjsvz@bogus> <1jimbak0hh.fsf@starbuckisacylon.baylibre.com> <20201016093421.7hyiqrekiy6mtyso@bogus> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201016093421.7hyiqrekiy6mtyso@bogus> User-Agent: NeoMutt/20171215 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Oct 16, 2020 at 10:34:21AM +0100, Sudeep Holla wrote: > On Fri, Oct 16, 2020 at 11:02:02AM +0200, Jerome Brunet wrote: > > > > On Fri 16 Oct 2020 at 10:44, Sudeep Holla wrote: > > > > > On Thu, Oct 15, 2020 at 03:29:35PM +0100, Ionela Voinescu wrote: > > >> Hi Jerome, > > >> > > >> On Thursday 15 Oct 2020 at 15:58:30 (+0200), Jerome Brunet wrote: > > >> > > > >> > On Thu 15 Oct 2020 at 15:46, Ionela Voinescu wrote: > > >> > > > >> > > Hi guys, > > >> > > > > >> > > On Wednesday 23 Sep 2020 at 14:39:16 (+0200), Jerome Brunet wrote: > > >> > >> If the txdone is done by polling, it is possible for msg_submit() to start > > >> > >> the timer while txdone_hrtimer() callback is running. If the timer needs > > >> > >> recheduling, it could already be enqueued by the time hrtimer_forward_now() > > >> > >> is called, leading hrtimer to loudly complain. > > >> > >> > > >> > >> WARNING: CPU: 3 PID: 74 at kernel/time/hrtimer.c:932 hrtimer_forward+0xc4/0x110 > > >> > >> CPU: 3 PID: 74 Comm: kworker/u8:1 Not tainted 5.9.0-rc2-00236-gd3520067d01c-dirty #5 > > >> > >> Hardware name: Libre Computer AML-S805X-AC (DT) > > >> > >> Workqueue: events_freezable_power_ thermal_zone_device_check > > >> > >> pstate: 20000085 (nzCv daIf -PAN -UAO BTYPE=--) > > >> > >> pc : hrtimer_forward+0xc4/0x110 > > >> > >> lr : txdone_hrtimer+0xf8/0x118 > > >> > >> [...] > > >> > >> > > >> > >> Canceling the timer before starting it ensure that the timer callback is > > >> > >> not running when the timer is started, solving this race condition. > > >> > >> > > >> > >> Fixes: 0cc67945ea59 ("mailbox: switch to hrtimer for tx_complete polling") > > >> > >> Reported-by: Da Xue > > >> > >> Signed-off-by: Jerome Brunet > > >> > >> --- > > >> > >> drivers/mailbox/mailbox.c | 8 ++++++-- > > >> > >> 1 file changed, 6 insertions(+), 2 deletions(-) > > >> > >> > > >> > >> diff --git a/drivers/mailbox/mailbox.c b/drivers/mailbox/mailbox.c > > >> > >> index 0b821a5b2db8..34f9ab01caef 100644 > > >> > >> --- a/drivers/mailbox/mailbox.c > > >> > >> +++ b/drivers/mailbox/mailbox.c > > >> > >> @@ -82,9 +82,13 @@ static void msg_submit(struct mbox_chan *chan) > > >> > >> exit: > > >> > >> spin_unlock_irqrestore(&chan->lock, flags); > > >> > >> > > >> > >> - if (!err && (chan->txdone_method & TXDONE_BY_POLL)) > > >> > >> - /* kick start the timer immediately to avoid delays */ > > >> > >> + if (!err && (chan->txdone_method & TXDONE_BY_POLL)) { > > >> > >> + /* Disable the timer if already active ... */ > > >> > >> + hrtimer_cancel(&chan->mbox->poll_hrt); > > >> > >> + > > >> > >> + /* ... and kick start it immediately to avoid delays */ > > >> > >> hrtimer_start(&chan->mbox->poll_hrt, 0, HRTIMER_MODE_REL); > > >> > >> + } > > >> > >> } > > >> > >> > > >> > >> static void tx_tick(struct mbox_chan *chan, int r) > > >> > > > > >> > > I've tracked a regression back to this commit. Details to reproduce: > > >> > > > >> > Hi Ionela, > > >> > > > >> > I don't have access to your platform and I don't get what is going on > > >> > from the log below. > > >> > > > >> > Could you please give us a bit more details about what is going on ? > > >> > > > >> > > >> I'm not familiar with the mailbox subsystem, so the best I can do right > > >> now is to add Sudeep to Cc, in case this conflicts in some way with the > > >> ARM MHU patches [1]. > > >> > > > > > > Not it can't be doorbell driver as we use SCPI(old firmware) with upstream > > > MHU driver as is limiting the number of channels to be used. > > > > > >> In the meantime I'll get some traces and get more familiar with the > > >> code. > > >> > > > > > > I will try that too. > > > > BTW, this issue was originally reported on amlogic platforms which also > > use arm,mhu mailbox driver. > > > > OK. Anyway just noticed that hrtimer_cancel uses hrtimer_try_to_cancel > and hrtimer_cancel_wait_running. The latter is just cpu_relax() if > PREEMPT_RT=n, so you may still have issue if the hrtimer is still active > or restarts in the meantime. > Scratch that, I failed to see the loop in hrtimer_cancel earlier. -- Regards, Sudeep