Commit b47bcab6 authored Mar 17, 2026 by Mauricio Faria de Oliveira Committed by Alexandre Belloni Mar 18, 2026

rtc: add data_race() in rtc_dev_poll()



The unlocked read of rtc->irq_data in rtc_dev_poll() can race with
the write in rtc_handle_legacy_irq() and also, theoretically, with
the write in rtc_dev_read().

These races should be safe (see inline comment), thus annotate the
read with data_race() for KCSAN.

Reported-by:  <syzbot+2d4127acca35ed7b31ad@syzkaller.appspotmail.com>
Closes: https://syzbot.org/bug?extid=2d4127acca35ed7b31ad


Signed-off-by: Mauricio Faria de Oliveira <mfo@igalia.com>
Link: https://patch.msgid.link/20260317-irq_data-v1-1-a2741002be60@igalia.com


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

parent 5827fe59

drivers/rtc/dev.c

+10 −1

Original line number	Diff line number	Diff line
		@@ -195,7 +195,16 @@ static __poll_t rtc_dev_poll(struct file file, poll_table wait)

		poll_wait(file, &rtc->irq_queue, wait);

		data = rtc->irq_data;
		/*
		* This read can race with the write in rtc_handle_legacy_irq().
		*
		* - If this check misses a zero to non-zero transition the next check
		* will pick it up (rtc_handle_legacy_irq() wakes up rtc->irq_queue).
		* - Non-zero to non-zero transition misses do not change return value.
		* - And a non-zero to zero transition is unlikely to be missed, since
		* it occurs on rtc_dev_read(), during which polling is not expected.
		*/
		data = data_race(rtc->irq_data);

		return (data != 0) ? (EPOLLIN \| EPOLLRDNORM) : 0;
		}