linux-kernel - Re: [PATCH tip] sched/trivial: Remove cfs bandwidth period check in tg_set_cfs

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Date:	Mon, 12 Dec 2011 14:05:16 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, Paul Turner <pjt@...gle.com>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH tip] sched/trivial: Remove cfs bandwidth period check in
 tg_set_cfs_period()

On Sat, 2011-12-10 at 19:29 +0530, Kamalesh Babulal wrote:
> sched: Remove cfs bandwidth period check in tg_set_cfs_period()
> 
> Remove cfs bandwidth period check from tg_set_cfs_period.
> Invalid bandwidth period's lower/upper limits are denoted
> by min_cfs_quota_period/max_cfs_quota_period repsectively,
> and are checked against valid period in tg_set_cfs_bandwidth().
> 
> Signed-off-by: Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>
> -- 
>  kernel/sched/core.c |    3 ---
>  1 files changed, 0 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 3c5b21e..57cf3ab 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -7689,9 +7689,6 @@ int tg_set_cfs_period(struct task_group *tg, long cfs_period_us)
>         period = (u64)cfs_period_us * NSEC_PER_USEC;
>         quota = tg->cfs_bandwidth.quota;
>  
> -       if (period <= 0)
> -               return -EINVAL;
> -
>         return tg_set_cfs_bandwidth(tg, period, quota);
>  } 

There's a number of funnies here... it checks an unsigned value for <=
0, which suggests it wanted to check cfs_period_us, which is a signed
value.

tg_set_cfs_bandwidth() has the same problem, at that point everything is
unsigned and all below zero checks will fail.

Please reconsider things and see if this patch is still the right one.
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