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From: Odin Ugedal <odin@uged.al>
To: Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
	Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: linux-kernel@vger.kernel.org, Odin Ugedal <odin@uged.al>
Subject: [PATCH] sched/fair: Fix CFS bandwidth hrtimer expiry type
Date: Tue, 29 Jun 2021 14:14:52 +0200	[thread overview]
Message-ID: <20210629121452.18429-1-odin@uged.al> (raw)

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>
---
 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;
-- 
2.32.0


             reply	other threads:[~2021-06-29 12:18 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-29 12:14 Odin Ugedal [this message]
2021-06-29 20:55 ` Benjamin Segall
2021-07-05  7:53 ` [tip: sched/urgent] " tip-bot2 for Odin Ugedal

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