Commit 72d0ad7c authored by Odin Ugedal's avatar Odin Ugedal Committed by Peter Zijlstra
Browse files

sched/fair: Fix CFS bandwidth hrtimer expiry type 



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: default avatarOdin Ugedal <odin@uged.al>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarBen Segall <bsegall@google.com>
Link: https://lore.kernel.org/r/20210629121452.18429-1-odin@uged.al
parent ceb6ba45

kernel/sched/fair.c

+2 −2
Original line number Diff line number Diff line
@@ -5054,7 +5054,7 @@ 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))
@@ -5062,7 +5062,7 @@ 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;