This is a note to let you know that I've just added the patch titled sched/fair: Fix CFS bandwidth hrtimer expiry type to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: sched-fair-fix-cfs-bandwidth-hrtimer-expiry-type.patch and it can be found in the queue-4.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit bae6d16e06b848b982c986e939dfdf31678319bb Author: Odin Ugedal <odin@xxxxxxx> Date: Tue Jun 29 14:14:52 2021 +0200 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@xxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Reviewed-by: Ben Segall <bsegall@xxxxxxxxxx> Link: https://lore.kernel.org/r/20210629121452.18429-1-odin@xxxxxxx Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 15952d0e340b..e00f17070cb2 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3852,7 +3852,7 @@ 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)) @@ -3860,7 +3860,7 @@ 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;