Messages in this thread | | | From | Jassi Brar <> | Date | Fri, 16 Oct 2020 12:33:57 -0500 | Subject | Re: [PATCH] mailbox: cancel timer before starting it |
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On Fri, Oct 16, 2020 at 4:00 AM Jerome Brunet <jbrunet@baylibre.com> wrote: > > > On Fri 16 Oct 2020 at 10:52, Ionela Voinescu <ionela.voinescu@arm.com> wrote: > > > On Thursday 15 Oct 2020 at 13:45:54 (-0500), Jassi Brar wrote: > > [..] > >> > >> --- 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 ? > >> > > >> > All this patch does is add hrtimer_cancel(). > >> > * It is needed if the timer had already been started, which is > >> > appropriate AFAIU > >> > * It is a NO-OP is the timer is not active. > >> > > >> Can you please try using hrtimer_try_to_cancel() instead ? > >> > > > > Yes, using hrtimer_try_to_cancel() instead works for me. But doesn't > > this limit how effective this change is? AFAIU, this will possibly only > > reduce the chances for the race condition, but not solve it. > > > > It is also my understanding, hrtimer_try_to_cancel() would remove a > timer which as not already started but would return withtout doing > anything if the callback is already running ... which is the original > problem > If we are running in the callback path, hrtimer_try_to_cancel will return -1, in which case we could skip hrtimer_start. Anyways, I think simply checking for hrtimer_active should effect the same. I have submitted a patch, of course not tested.
Thanks
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