[PATCH] mailbox: avoid timer start from callback

[jassisinghbrar]

From: Jassi Brar <jaswinder.singh@xxxxxxxxxx>

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@xxxxxxxxxx>
---
 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 */
+		if (!hrtimer_active(&chan->mbox->poll_hrt))
+			hrtimer_start(&chan->mbox->poll_hrt, 0, HRTIMER_MODE_REL);
+	}
 }
 
 static void tx_tick(struct mbox_chan *chan, int r)
@@ -122,11 +125,10 @@ static enum hrtimer_restart txdone_hrtimer(struct hrtimer *hrtimer)
 		struct mbox_chan *chan = &mbox->chans[i];
 
 		if (chan->active_req && chan->cl) {
+			resched = true;
 			txdone = chan->mbox->ops->last_tx_done(chan);
 			if (txdone)
 				tx_tick(chan, 0);
-			else
-				resched = true;
 		}
 	}
 
-- 
2.25.1