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Commit 7ea0a719 authored by Eric Dumazet's avatar Eric Dumazet Committed by Greg Kroah-Hartman
Browse files

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: d94ba80e ("ptp: Added a brand new class driver for ptp clocks.")
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Acked-by: default avatarRichard Cochran <richardcochran@gmail.com>
Link: https://lore.kernel.org/r/20231109174859.3995880-1-edumazet@google.com


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent 89af55e0

drivers/ptp/ptp_chardev.c

+2 −1
Original line number Diff line number Diff line
@@ -443,7 +443,8 @@ ssize_t ptp_read(struct posix_clock *pc, 


	for (i = 0; i < cnt; i++) {

		event[i] = queue->buf[queue->head];

		queue->head = (queue->head + 1) % PTP_MAX_TIMESTAMPS;

		/* Paired with READ_ONCE() in queue_cnt() */

		WRITE_ONCE(queue->head, (queue->head + 1) % PTP_MAX_TIMESTAMPS);

	}



	spin_unlock_irqrestore(&queue->lock, flags);

drivers/ptp/ptp_clock.c

+3 −2
Original line number Diff line number Diff line
@@ -55,10 +55,11 @@ static void enqueue_external_timestamp(struct timestamp_event_queue *queue, 
	dst->t.sec = seconds;

	dst->t.nsec = remainder;



	/* Both WRITE_ONCE() are paired with READ_ONCE() in queue_cnt() */

	if (!queue_free(queue))

		queue->head = (queue->head + 1) % PTP_MAX_TIMESTAMPS;

		WRITE_ONCE(queue->head, (queue->head + 1) % PTP_MAX_TIMESTAMPS);



	queue->tail = (queue->tail + 1) % PTP_MAX_TIMESTAMPS;

	WRITE_ONCE(queue->tail, (queue->tail + 1) % PTP_MAX_TIMESTAMPS);



	spin_unlock_irqrestore(&queue->lock, flags);

}

drivers/ptp/ptp_private.h

+6 −2
Original line number Diff line number Diff line
@@ -55,9 +55,13 @@ struct ptp_clock { 
 * that a writer might concurrently increment the tail does not

 * matter, since the queue remains nonempty nonetheless.

 */

static inline int queue_cnt(struct timestamp_event_queue *q)

static inline int queue_cnt(const struct timestamp_event_queue *q)

{

	int cnt = q->tail - q->head;

	/*

	 * Paired with WRITE_ONCE() in enqueue_external_timestamp(),

	 * ptp_read(), extts_fifo_show().

	 */

	int cnt = READ_ONCE(q->tail) - READ_ONCE(q->head);

	return cnt < 0 ? PTP_MAX_TIMESTAMPS + cnt : cnt;

}

drivers/ptp/ptp_sysfs.c

+2 −1
Original line number Diff line number Diff line
@@ -78,7 +78,8 @@ static ssize_t extts_fifo_show(struct device *dev, 
	qcnt = queue_cnt(queue);

	if (qcnt) {

		event = queue->buf[queue->head];

		queue->head = (queue->head + 1) % PTP_MAX_TIMESTAMPS;

		/* Paired with READ_ONCE() in queue_cnt() */

		WRITE_ONCE(queue->head, (queue->head + 1) % PTP_MAX_TIMESTAMPS);

	}

	spin_unlock_irqrestore(&queue->lock, flags);