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media: cec-pin: Fix event FIFO ordering

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cec_pin_update() fills work_pin_events[] and work_pin_ts[], then
increments work_pin_num_events. cec_pin_thread_func() uses that counter
to decide when to read the FIFO entries.

Do not let the counter update be observed without the event update. Also
do not let a freed slot be reused before the thread has finished reading
it. Use release operations when publishing an entry and releasing a slot,
and acquire operations when consuming those counter updates.

Leave the other work_pin_num_events users as they do not participate in
this FIFO publication path.

Fixes: ea5c8ef296 ("media: cec-pin: add low-level pin hardware support")
Signed-off-by: Gui-Dong Han <hanguidong02@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>
This commit is contained in:
Gui-Dong Han 2026-06-26 16:08:06 +08:00 committed by Hans Verkuil
parent 3bc2e4a264
commit a1d83d1b81
1 changed files with 4 additions and 4 deletions
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8
drivers/media/cec/core/cec-pin.c
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@ -115,7 +115,7 @@ static void cec_pin_update(struct cec_pin *pin, bool v, bool force)
return;
pin->adap->cec_pin_is_high = v;
if (atomic_read(&pin->work_pin_num_events) < CEC_NUM_PIN_EVENTS) {
if (atomic_read_acquire(&pin->work_pin_num_events) < CEC_NUM_PIN_EVENTS) {
u8 ev = v;
if (pin->work_pin_events_dropped) {
@ -126,7 +126,7 @@ static void cec_pin_update(struct cec_pin *pin, bool v, bool force)
pin->work_pin_ts[pin->work_pin_events_wr] = ktime_get();
pin->work_pin_events_wr =
(pin->work_pin_events_wr + 1) % CEC_NUM_PIN_EVENTS;
atomic_inc(&pin->work_pin_num_events);
atomic_inc_return_release(&pin->work_pin_num_events);
} else {
pin->work_pin_events_dropped = true;
pin->work_pin_events_dropped_cnt++;
@ -1101,7 +1101,7 @@ static int cec_pin_thread_func(void *_adap)
pin->work_tx_ts);
}
while (atomic_read(&pin->work_pin_num_events)) {
while (atomic_read_acquire(&pin->work_pin_num_events)) {
unsigned int idx = pin->work_pin_events_rd;
u8 v = pin->work_pin_events[idx];
@ -1110,7 +1110,7 @@ static int cec_pin_thread_func(void *_adap)
v & CEC_PIN_EVENT_FL_DROPPED,
pin->work_pin_ts[idx]);
pin->work_pin_events_rd = (idx + 1) % CEC_NUM_PIN_EVENTS;
atomic_dec(&pin->work_pin_num_events);
atomic_dec_return_release(&pin->work_pin_num_events);
}
switch (atomic_xchg(&pin->work_irq_change,