From: santosh.shilimkar@ti•com (Santosh Shilimkar)
To: linux-arm-kernel@lists•infradead.org
Subject: [RFC 4/6] sched: secure access to other CPU statistics
Date: Wed, 24 Oct 2012 20:51:17 +0530 [thread overview]
Message-ID: <5088076D.6080208@ti.com> (raw)
In-Reply-To: <1349595838-31274-5-git-send-email-vincent.guittot@linaro.org>
$subject is bit confusing here.
On Sunday 07 October 2012 01:13 PM, Vincent Guittot wrote:
> The atomic update of runnable_avg_sum and runnable_avg_period are ensured
> by their size and the toolchain. But we must ensure to not read an old value
> for one field and a newly updated value for the other field. As we don't
> want to lock other CPU while reading these fields, we read twice each fields
> and check that no change have occured in the middle.
>
> Signed-off-by: Vincent Guittot <vincent.guittot@linaro•org>
> ---
> kernel/sched/fair.c | 19 +++++++++++++++++--
> 1 file changed, 17 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 8c9d3ed..6df53b5 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3133,13 +3133,28 @@ static int select_idle_sibling(struct task_struct *p, int target)
> static inline bool is_buddy_busy(int cpu)
> {
> struct rq *rq = cpu_rq(cpu);
> + volatile u32 *psum = &rq->avg.runnable_avg_sum;
> + volatile u32 *pperiod = &rq->avg.runnable_avg_period;
> + u32 sum, new_sum, period, new_period;
> + int timeout = 10;
So it can be 2 times read or more as well.
> +
> + while (timeout) {
> + sum = *psum;
> + period = *pperiod;
> + new_sum = *psum;
> + new_period = *pperiod;
> +
> + if ((sum == new_sum) && (period == new_period))
> + break;
> +
> + timeout--;
> + }
>
Seems like you did notice incorrect pair getting read
for rq runnable_avg_sum and runnable_avg_period. Seems
like the fix is to update them together under some lock
to avoid such issues.
Regards
Santosh
next prev parent reply other threads:[~2012-10-24 15:21 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-10-07 7:43 [RFC 0/6] sched: packing small tasks Vincent Guittot
2012-10-07 7:43 ` [RFC 1/6] Revert "sched: introduce temporary FAIR_GROUP_SCHED dependency for load-tracking" Vincent Guittot
2012-10-07 7:43 ` [RFC 2/6] sched: add a new SD SHARE_POWERLINE flag for sched_domain Vincent Guittot
2012-10-24 15:17 ` Santosh Shilimkar
2012-10-29 9:40 ` Vincent Guittot
2012-10-29 9:50 ` Vincent Guittot
2012-11-02 10:27 ` Santosh Shilimkar
2012-10-07 7:43 ` [RFC 3/6] sched: pack small tasks Vincent Guittot
2012-10-24 15:20 ` Santosh Shilimkar
2012-10-29 13:12 ` Vincent Guittot
2012-11-02 10:53 ` Santosh Shilimkar
2012-11-09 16:46 ` Morten Rasmussen
2012-11-12 13:13 ` Vincent Guittot
2012-11-12 9:30 ` Vincent Guittot
2012-11-09 17:13 ` Morten Rasmussen
2012-11-12 13:51 ` Vincent Guittot
2012-11-20 14:28 ` Morten Rasmussen
2012-11-20 16:59 ` Vincent Guittot
2012-10-07 7:43 ` [RFC 4/6] sched: secure access to other CPU statistics Vincent Guittot
2012-10-24 15:21 ` Santosh Shilimkar [this message]
2012-10-29 13:18 ` Vincent Guittot
2012-10-07 7:43 ` [RFC 5/6] sched: pack the idle load balance Vincent Guittot
2012-10-24 15:21 ` Santosh Shilimkar
2012-10-29 13:27 ` Vincent Guittot
2012-11-02 10:59 ` Santosh Shilimkar
2012-10-07 7:43 ` [RFC 6/6] ARM: sched: clear SD_SHARE_POWERLINE Vincent Guittot
2012-10-24 15:21 ` Santosh Shilimkar
2012-10-29 13:28 ` Vincent Guittot
2012-11-02 11:00 ` Santosh Shilimkar
2012-11-12 8:23 ` Vincent Guittot
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