linux-kernel - Re: [PATCH] mailbox: cancel timer before starting it

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Message-ID: <7hr1qr9l00.fsf@baylibre.com>
Date:   Thu, 24 Sep 2020 09:50:55 -0700
From:   Kevin Hilman <khilman@...libre.com>
To:     Jerome Brunet <jbrunet@...libre.com>,
        Jassi Brar <jassisinghbrar@...il.com>
Cc:     Jerome Brunet <jbrunet@...libre.com>,
        linux-amlogic@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Da Xue <da@...re.computer>
Subject: Re: [PATCH] mailbox: cancel timer before starting it

Jerome Brunet <jbrunet@...libre.com> writes:

> 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 <da@...re.computer>
> Signed-off-by: Jerome Brunet <jbrunet@...libre.com>

Reviewed-by: Kevin Hilman <khilman@...libre.com>

Kevin