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mailbox: forward the hrtimer if not queued and under a lock

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This reverts commit c7dacf5b0f,
"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: c7dacf5b0f ("mailbox: avoid timer start from callback")
Signed-off-by: Björn Ardö <bjorn.ardo@axis.com>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>
This commit is contained in:
Björn Ardö 2022-03-31 09:01:15 +02:00 committed by Jassi Brar
parent c25f778997
commit bca1a10046
2 changed files with 14 additions and 6 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

19
drivers/mailbox/mailbox.c
View file

@ -82,11 +82,11 @@ 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);
}
}
@ -120,20 +120,26 @@ 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;
@ -500,6 +506,7 @@ 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++) {

1
include/linux/mailbox_controller.h
View file

@ -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;
};