[PATCH 4.14 096/218] mailbox: forward the hrtimer if not queued and under a lock

Greg Kroah-Hartman
2022-06-13T10:50:06Z

From: Björn Ardö <bjorn.ardo@axis.com>

[ Upstream commit bca1a1004615efe141fd78f360ecc48c60bc4ad5 ]

This reverts commit c7dacf5b0f32957b24ef29df1207dc2cd8307743,
"mailbox: avoid timer start from callback"

The previous commit was reverted since it lead to a race that
caused the hrtimer to not be started at all. The check for
hrtimer_active() in msg_submit() will return true if the
callback function txdone_hrtimer() is currently running. This
function could return HRTIMER_NORESTART and then the timer
will not be restarted, and also msg_submit() will not start
the timer. This will lead to a message actually being submitted
but no timer will start to check for its compleation.

The original fix that added checking hrtimer_active() was added to
avoid a warning with hrtimer_forward. Looking in the kernel
another solution to avoid this warning is to check hrtimer_is_queued()
before calling hrtimer_forward_now() instead. This however requires a
lock so the timer is not started by msg_submit() inbetween this check
and the hrtimer_forward() call.

Fixes: c7dacf5b0f32 ("mailbox: avoid timer start from callback")
Signed-off-by: Björn Ardö <bjorn.ardo@axis.com>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/mailbox/mailbox.c | 19 +++++++++++++------
include/linux/mailbox_controller.h | 1 +
2 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/drivers/mailbox/mailbox.c b/drivers/mailbox/mailbox.c
index 10a559cfb7ea..aa28fdcb81b9 100644
--- a/drivers/mailbox/mailbox.c
+++ b/drivers/mailbox/mailbox.c
@@ -85,11 +85,11 @@ static void msg_submit(struct mbox_chan *chan)
exit:
spin_unlock_irqrestore(&chan->lock, flags);

- /* 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);
+ /* kick start the timer immediately to avoid delays */
+ spin_lock_irqsave(&chan->mbox->poll_hrt_lock, flags);
+ hrtimer_start(&chan->mbox->poll_hrt, 0, HRTIMER_MODE_REL);
+ spin_unlock_irqrestore(&chan->mbox->poll_hrt_lock, flags);
}
}

@@ -123,20 +123,26 @@ static enum hrtimer_restart txdone_hrtimer(struct hrtimer *hrtimer)
container_of(hrtimer, struct mbox_controller, poll_hrt);
bool txdone, resched = false;
int i;
+ unsigned long flags;

for (i = 0; i < mbox->num_chans; i++) {
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;
}
}

if (resched) {
- hrtimer_forward_now(hrtimer, ms_to_ktime(mbox->txpoll_period));
+ spin_lock_irqsave(&mbox->poll_hrt_lock, flags);
+ if (!hrtimer_is_queued(hrtimer))
+ hrtimer_forward_now(hrtimer, ms_to_ktime(mbox->txpoll_period));
+ spin_unlock_irqrestore(&mbox->poll_hrt_lock, flags);
+
return HRTIMER_RESTART;
}
return HRTIMER_NORESTART;
@@ -473,6 +479,7 @@ int mbox_controller_register(struct mbox_controller *mbox)
hrtimer_init(&mbox->poll_hrt, CLOCK_MONOTONIC,
HRTIMER_MODE_REL);
mbox->poll_hrt.function = txdone_hrtimer;
+ spin_lock_init(&mbox->poll_hrt_lock);
}

for (i = 0; i < mbox->num_chans; i++) {
diff --git a/include/linux/mailbox_controller.h b/include/linux/mailbox_controller.h
index 74deadb42d76..5a4524f66ea1 100644
--- a/include/linux/mailbox_controller.h
+++ b/include/linux/mailbox_controller.h
@@ -83,6 +83,7 @@ struct mbox_controller {
const struct of_phandle_args *sp);
/* Internal to API */
struct hrtimer poll_hrt;
+ spinlock_t poll_hrt_lock;
struct list_head node;
};

--
2.35.1