linux-kernel - Re: [PATCH] mailbox: avoid timer start from callback

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Message-ID: <20201016175039.7xs4cafoe2uq7zus@bogus>
Date:   Fri, 16 Oct 2020 18:50:39 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     jassisinghbrar@...il.com
Cc:     linux-kernel@...r.kernel.org, linux-amlogic@...ts.infradead.org,
        jbrunet@...libre.com, ionela.voinescu@....com,
        khilman@...libre.com, da@...re.computer,
        Jassi Brar <jaswinder.singh@...aro.org>,
        Sudeep Holla <sudeep.holla@....com>
Subject: Re: [PATCH] mailbox: avoid timer start from callback

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.

--
Regards,
Sudeep