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Date:   Fri, 16 Oct 2020 13:24:56 -0500
From:   Jassi Brar <jassisinghbrar@...il.com>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:ARM/Amlogic Meson..." <linux-amlogic@...ts.infradead.org>,
        Jerome Brunet <jbrunet@...libre.com>,
        Ionela Voinescu <ionela.voinescu@....com>,
        Kevin Hilman <khilman@...libre.com>,
        Da Xue <da@...re.computer>,
        Jassi Brar <jaswinder.singh@...aro.org>
Subject: Re: [PATCH] mailbox: avoid timer start from callback

On Fri, Oct 16, 2020 at 12:50 PM Sudeep Holla <sudeep.holla@....com> wrote:
>
> On Fri, Oct 16, 2020 at 12:30:20PM -0500, jassisinghbrar@...il.com wrote:
> > From: Jassi Brar <jaswinder.singh@...aro.org>
> >
> > 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
> > [...]
> >
> > This can be fixed by not starting the timer from the callback path. Which
> > requires the timer reloading as long as any message is queued on the
> > channel, and not just when current tx is not done yet.
> >
>
> I came to similar conclusion and was testing something similar. You bet
> me. Since we have single timer and multiple channels, each time a message
> is enqueued on any channel, timer gets added which is wrong.
>
> Reviewed-by: Sudeep Holla <sudeep.holla@....com>
>
> I tested this patch too by reverting offending commit in -next, so
>
> Tested-by: Sudeep Holla <sudeep.holla@....com>
>
> You seem to have dropped the Fixes tags. Is that intentional ? If so,
> any particular reasons. I think it is stable material and better to have
> fixes tag so that it gets added to stable trees.
>
Thanks for testing. I will decorate it appropriately once I have
Jerome's tested-by too.

-jassi

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