* [PATCH] sched/fair: Fix CFS bandwidth hrtimer expiry type
@ 2021-06-29 12:14 Odin Ugedal
2021-06-29 20:55 ` Benjamin Segall
2021-07-05 7:53 ` [tip: sched/urgent] " tip-bot2 for Odin Ugedal
0 siblings, 2 replies; 3+ messages in thread
From: Odin Ugedal @ 2021-06-29 12:14 UTC (permalink / raw)
To: Ingo Molnar, Peter Zijlstra, Juri Lelli, Vincent Guittot,
Dietmar Eggemann, Steven Rostedt, Ben Segall, Mel Gorman,
Daniel Bristot de Oliveira
Cc: linux-kernel, Odin Ugedal
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
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] sched/fair: Fix CFS bandwidth hrtimer expiry type
2021-06-29 12:14 [PATCH] sched/fair: Fix CFS bandwidth hrtimer expiry type Odin Ugedal
@ 2021-06-29 20:55 ` Benjamin Segall
2021-07-05 7:53 ` [tip: sched/urgent] " tip-bot2 for Odin Ugedal
1 sibling, 0 replies; 3+ messages in thread
From: Benjamin Segall @ 2021-06-29 20:55 UTC (permalink / raw)
To: Odin Ugedal
Cc: Ingo Molnar, Peter Zijlstra, Juri Lelli, Vincent Guittot,
Dietmar Eggemann, Steven Rostedt, Mel Gorman,
Daniel Bristot de Oliveira, linux-kernel
Odin Ugedal <odin@uged.al> writes:
> 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.
Yeah, extremely rare, not any real sort of problem when it does happen,
but no reason not to fix it and get the slight win in precision.
Reviewed-by: Ben Segall <bsegall@google.com>
>
> 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;
^ permalink raw reply [flat|nested] 3+ messages in thread
* [tip: sched/urgent] sched/fair: Fix CFS bandwidth hrtimer expiry type
2021-06-29 12:14 [PATCH] sched/fair: Fix CFS bandwidth hrtimer expiry type Odin Ugedal
2021-06-29 20:55 ` Benjamin Segall
@ 2021-07-05 7:53 ` tip-bot2 for Odin Ugedal
1 sibling, 0 replies; 3+ messages in thread
From: tip-bot2 for Odin Ugedal @ 2021-07-05 7:53 UTC (permalink / raw)
To: linux-tip-commits
Cc: Odin Ugedal, Peter Zijlstra (Intel), Ben Segall, x86, linux-kernel
The following commit has been merged into the sched/urgent branch of tip:
Commit-ID: 72d0ad7cb5bad265adb2014dbe46c4ccb11afaba
Gitweb: https://git.kernel.org/tip/72d0ad7cb5bad265adb2014dbe46c4ccb11afaba
Author: Odin Ugedal <odin@uged.al>
AuthorDate: Tue, 29 Jun 2021 14:14:52 +02:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Fri, 02 Jul 2021 15:58:24 +02:00
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: 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
---
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 1e263c9..1b15a19 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -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;
^ permalink raw reply related [flat|nested] 3+ messages in thread
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2021-06-29 12:14 [PATCH] sched/fair: Fix CFS bandwidth hrtimer expiry type Odin Ugedal
2021-06-29 20:55 ` Benjamin Segall
2021-07-05 7:53 ` [tip: sched/urgent] " tip-bot2 for Odin Ugedal
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