On Fri 16 Oct 2020 at 10:44, Sudeep Holla <sudeep.ho...@arm.com> wrote:
> On Thu, Oct 15, 2020 at 03:29:35PM +0100, Ionela Voinescu wrote: >> Hi Jerome, >> >> On Thursday 15 Oct 2020 at 15:58:30 (+0200), Jerome Brunet wrote: >> > >> > On Thu 15 Oct 2020 at 15:46, Ionela Voinescu <ionela.voine...@arm.com> >> > wrote: >> > >> > > Hi guys, >> > > >> > > On Wednesday 23 Sep 2020 at 14:39:16 (+0200), Jerome Brunet wrote: >> > >> 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@libre.computer> >> > >> Signed-off-by: Jerome Brunet <jbru...@baylibre.com> >> > >> --- >> > >> drivers/mailbox/mailbox.c | 8 ++++++-- >> > >> 1 file changed, 6 insertions(+), 2 deletions(-) >> > >> >> > >> diff --git a/drivers/mailbox/mailbox.c b/drivers/mailbox/mailbox.c >> > >> index 0b821a5b2db8..34f9ab01caef 100644 >> > >> --- 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 ? >> > >> >> I'm not familiar with the mailbox subsystem, so the best I can do right >> now is to add Sudeep to Cc, in case this conflicts in some way with the >> ARM MHU patches [1]. >> > > Not it can't be doorbell driver as we use SCPI(old firmware) with upstream > MHU driver as is limiting the number of channels to be used. > >> In the meantime I'll get some traces and get more familiar with the >> code. >> > > I will try that too. BTW, this issue was originally reported on amlogic platforms which also use arm,mhu mailbox driver.