sched/fair: Fix CFS bandwidth hrtimer expiry type

[ Upstream commit 72d0ad7cb5bad265adb2014dbe46c4ccb11afaba ]

The time remaining until expiry of the refresh_timer can be negative.
Casting the type to an unsigned 64-bit value will cause integer
underflow, making the runtime_refresh_within return false instead of
true. These situations are rare, but they do happen.

This does not cause user-facing issues or errors; other than
possibly unthrottling cfs_rq's using runtime from the previous period(s),
making the CFS bandwidth enforcement less strict in those (special)
situations.

Signed-off-by: Odin Ugedal <odin@uged.al>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ben Segall <bsegall@google.com>
Link: https://lore.kernel.org/r/20210629121452.18429-1-odin@uged.al
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 9cdbc07bb70f379e427a56bd9a2b50fef5c6fbb3..84e7efda98dafa80703c00343798766de5dc17ed 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4714,7 +4714,7 @@ static const u64 cfs_bandwidth_slack_period = 5 * NSEC_PER_MSEC;
 static int runtime_refresh_within(struct cfs_bandwidth *cfs_b, u64 min_expire)
 {
        struct hrtimer *refresh_timer = &cfs_b->period_timer;
-       u64 remaining;
+       s64 remaining;
 
        /* if the call-back is running a quota refresh is already occurring */
        if (hrtimer_callback_running(refresh_timer))
@@ -4722,7 +4722,7 @@ static int runtime_refresh_within(struct cfs_bandwidth *cfs_b, u64 min_expire)
 
        /* is a quota refresh about to occur? */
        remaining = ktime_to_ns(hrtimer_expires_remaining(refresh_timer));
-       if (remaining < min_expire)
+       if (remaining < (s64)min_expire)
                return 1;
 
        return 0;