[PATCH 6.19 033/844] rtc: interface: Alarm race handling should not discard preceding error

[Sasha Levin]

From: "Anthony Pighin (Nokia)" <anthony.pighin@xxxxxxxxx>

[ Upstream commit 81be22cd4ace020045cc6d31255c6f7c071eb7c0 ]

Commit 795cda8338ea ("rtc: interface: Fix long-standing race when setting
alarm") should not discard any errors from the preceding validations.

Prior to that commit, if the alarm feature was disabled, or the
set_alarm failed, a meaningful error code would be returned to the
caller for further action.

After, more often than not, the __rtc_read_time will cause a success
return code instead, misleading the caller.

An example of this is when timer_enqueue is called for a rtc-abx080x
device. Since that driver does not clear the alarm feature bit, but
instead relies on the set_alarm operation to return invalid, the discard
of the return code causes very different behaviour; i.e.
    hwclock: select() to /dev/rtc0 to wait for clock tick timed out

Fixes: 795cda8338ea ("rtc: interface: Fix long-standing race when setting alarm")
Signed-off-by: Anthony Pighin (Nokia) <anthony.pighin@xxxxxxxxx>
Reviewed-by: Esben Haabendal <esben@xxxxxxxxxx>
Tested-by: Nick Bowler <nbowler@xxxxxxxxxx>
Link: https://patch.msgid.link/BN0PR08MB6951415A751F236375A2945683D1A@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Alexandre Belloni <alexandre.belloni@xxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/rtc/interface.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/rtc/interface.c b/drivers/rtc/interface.c
index b8b298efd9a9c..1906f4884a834 100644
--- a/drivers/rtc/interface.c
+++ b/drivers/rtc/interface.c
@@ -457,7 +457,7 @@ static int __rtc_set_alarm(struct rtc_device *rtc, struct rtc_wkalrm *alarm)
 	 * are in, we can return -ETIME to signal that the timer has already
 	 * expired, which is true in both cases.
 	 */
-	if ((scheduled - now) <= 1) {
+	if (!err && (scheduled - now) <= 1) {
 		err = __rtc_read_time(rtc, &tm);
 		if (err)
 			return err;
-- 
2.51.0