ptp: annotate data-race around q->head and q->tail
[ Upstream commit 73bde5a3294853947252cd9092a3517c7cb0cd2d ]
As I was working on a syzbot report, I found that KCSAN would
probably complain that reading q->head or q->tail without
barriers could lead to invalid results.
Add corresponding READ_ONCE() and WRITE_ONCE() to avoid
load-store tearing.
Fixes: d94ba80ebb
("ptp: Added a brand new class driver for ptp clocks.")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Link: https://lore.kernel.org/r/20231109174859.3995880-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
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@ -443,7 +443,8 @@ ssize_t ptp_read(struct posix_clock *pc,
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for (i = 0; i < cnt; i++) {
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for (i = 0; i < cnt; i++) {
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event[i] = queue->buf[queue->head];
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event[i] = queue->buf[queue->head];
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queue->head = (queue->head + 1) % PTP_MAX_TIMESTAMPS;
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/* Paired with READ_ONCE() in queue_cnt() */
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WRITE_ONCE(queue->head, (queue->head + 1) % PTP_MAX_TIMESTAMPS);
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}
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}
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spin_unlock_irqrestore(&queue->lock, flags);
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spin_unlock_irqrestore(&queue->lock, flags);
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@ -55,10 +55,11 @@ static void enqueue_external_timestamp(struct timestamp_event_queue *queue,
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dst->t.sec = seconds;
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dst->t.sec = seconds;
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dst->t.nsec = remainder;
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dst->t.nsec = remainder;
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/* Both WRITE_ONCE() are paired with READ_ONCE() in queue_cnt() */
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if (!queue_free(queue))
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if (!queue_free(queue))
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queue->head = (queue->head + 1) % PTP_MAX_TIMESTAMPS;
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WRITE_ONCE(queue->head, (queue->head + 1) % PTP_MAX_TIMESTAMPS);
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queue->tail = (queue->tail + 1) % PTP_MAX_TIMESTAMPS;
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WRITE_ONCE(queue->tail, (queue->tail + 1) % PTP_MAX_TIMESTAMPS);
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spin_unlock_irqrestore(&queue->lock, flags);
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spin_unlock_irqrestore(&queue->lock, flags);
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}
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}
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@ -55,9 +55,13 @@ struct ptp_clock {
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* that a writer might concurrently increment the tail does not
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* that a writer might concurrently increment the tail does not
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* matter, since the queue remains nonempty nonetheless.
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* matter, since the queue remains nonempty nonetheless.
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*/
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*/
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static inline int queue_cnt(struct timestamp_event_queue *q)
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static inline int queue_cnt(const struct timestamp_event_queue *q)
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{
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{
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int cnt = q->tail - q->head;
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/*
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* Paired with WRITE_ONCE() in enqueue_external_timestamp(),
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* ptp_read(), extts_fifo_show().
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*/
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int cnt = READ_ONCE(q->tail) - READ_ONCE(q->head);
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return cnt < 0 ? PTP_MAX_TIMESTAMPS + cnt : cnt;
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return cnt < 0 ? PTP_MAX_TIMESTAMPS + cnt : cnt;
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}
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}
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@ -78,7 +78,8 @@ static ssize_t extts_fifo_show(struct device *dev,
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qcnt = queue_cnt(queue);
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qcnt = queue_cnt(queue);
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if (qcnt) {
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if (qcnt) {
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event = queue->buf[queue->head];
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event = queue->buf[queue->head];
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queue->head = (queue->head + 1) % PTP_MAX_TIMESTAMPS;
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/* Paired with READ_ONCE() in queue_cnt() */
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WRITE_ONCE(queue->head, (queue->head + 1) % PTP_MAX_TIMESTAMPS);
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}
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}
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spin_unlock_irqrestore(&queue->lock, flags);
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spin_unlock_irqrestore(&queue->lock, flags);
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