[PATCH] mailbox: avoid timer start from callback

[Jassi Brar]

On Fri, Oct 16, 2020 at 1:38 PM Jerome Brunet <jbrunet at baylibre.com> wrote:
>
>
> On Fri 16 Oct 2020 at 19:30, jassisinghbrar at gmail.com wrote:
>
> > From: Jassi Brar <jaswinder.singh at linaro.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.
> >
> > Signed-off-by: Jassi Brar <jaswinder.singh at linaro.org>
> > ---
> >  drivers/mailbox/mailbox.c | 12 +++++++-----
> >  1 file changed, 7 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/mailbox/mailbox.c b/drivers/mailbox/mailbox.c
> > index 0b821a5b2db8..a093a6ecaa66 100644
> > --- a/drivers/mailbox/mailbox.c
> > +++ b/drivers/mailbox/mailbox.c
> > @@ -82,9 +82,12 @@ 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 */
> > -             hrtimer_start(&chan->mbox->poll_hrt, 0, HRTIMER_MODE_REL);
> > +     /* kick start the timer immediately to avoid delays */
> > +     if (!err && (chan->txdone_method & TXDONE_BY_POLL)) {
> > +             /* but only if not already active */
>
> It would solve the problem I reported as well but instead of running the
> check immediately (timer with value 0), we will have to wait for the
> next of the timer, it is already started. IOW, there might be a delay
> now. I don't know if this important for the mailbox - the existing
> comments in the code suggested it was.
>
That comment is for when the first message is queued on the channel,
which remains unimpacted.
So, do I have your tested/acked by ?

thnx,