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ptp: annotate data-race around q->head and q->tail

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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>
This commit is contained in:
Eric Dumazet 2023-11-09 17:48:59 +00:00 • committed by Jakub Kicinski
parent 4b3812d90b
commit 73bde5a329
4 changed files with 13 additions and 6 deletions
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3
drivers/ptp/ptp_chardev.c
View file

@ -572,7 +572,8 @@ ssize_t ptp_read(struct posix_clock_context *pccontext, uint rdflags,
for (i = 0; i < cnt; i++) { for (i = 0; i < cnt; i++) {
event[i] = queue->buf[queue->head]; 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); spin_unlock_irqrestore(&queue->lock, flags);

5
drivers/ptp/ptp_clock.c
View file

@ -57,10 +57,11 @@ static void enqueue_external_timestamp(struct timestamp_event_queue *queue,
dst->t.sec = seconds; dst->t.sec = seconds;
dst->t.nsec = remainder; dst->t.nsec = remainder;
/* Both WRITE_ONCE() are paired with READ_ONCE() in queue_cnt() */
if (!queue_free(queue)) 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); spin_unlock_irqrestore(&queue->lock, flags);
} }

8
drivers/ptp/ptp_private.h
View file

@ -85,9 +85,13 @@ struct ptp_vclock {
* that a writer might concurrently increment the tail does not * that a writer might concurrently increment the tail does not
* matter, since the queue remains nonempty nonetheless. * 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; return cnt < 0 ? PTP_MAX_TIMESTAMPS + cnt : cnt;
} }

3
drivers/ptp/ptp_sysfs.c
View file

@ -94,7 +94,8 @@ static ssize_t extts_fifo_show(struct device *dev,
qcnt = queue_cnt(queue); qcnt = queue_cnt(queue);
if (qcnt) { if (qcnt) {
event = queue->buf[queue->head]; 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); spin_unlock_irqrestore(&queue->lock, flags);