Thread (111 messages) 111 messages, 2 authors, 2021-07-15
STALE1780d REVIEWED: 1 (1M)

[PATCH AUTOSEL 5.13 103/108] sched/fair: Fix CFS bandwidth hrtimer expiry type

From: Sasha Levin <sashal@kernel.org>
Date: 2021-07-14 19:43:06
Also in: lkml
Subsystem: scheduler, the rest · Maintainers: Ingo Molnar, Peter Zijlstra, Juri Lelli, Vincent Guittot, Linus Torvalds

From: Odin Ugedal <redacted>

[ 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 <redacted>
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 (local)
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/sched/fair.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 23663318fb81..62446c052efb 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5108,7 +5108,7 @@ 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))
@@ -5116,7 +5116,7 @@ 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;
-- 
2.30.2
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