Re: deadlock in setting schedule parameters

[Peter Zijlstra <peterz@infradead.org>]

On Wed, 2008-09-10 at 17:00 -0700, Hiroshi Shimamoto wrote:
> Andrei Gusev wrote:
> > Hello!
> > 
> > I played witch scheduler settings. After doing something like:
> > echo -n 1000000 >sched_rt_period_us
> > 
> > command is looked. I found in kernel.log
> > Sep 11 00:39:34 zaratustra
> > Sep 11 00:39:34 zaratustra Pid: 4495, comm: bash Tainted: G        W 
> > (2.6.26.3 #12)
> > Sep 11 00:39:34 zaratustra EIP: 0060:[<c0213fc7>] EFLAGS: 00210246 CPU: 0
> > Sep 11 00:39:34 zaratustra EIP is at div64_u64+0x57/0x80
> > Sep 11 00:39:34 zaratustra EAX: 0000389f EBX: 00000000 ECX: 00000000 
> > EDX: 00000000
> > Sep 11 00:39:34 zaratustra ESI: d9800000 EDI: d9800000 EBP: 0000389f 
> > ESP: ea7a6edc
> > Sep 11 00:39:34 zaratustra DS: 007b ES: 007b FS: 0000 GS: 0033 SS: 0068
> > Sep 11 00:39:34 zaratustra Process bash (pid: 4495, ti=ea7a6000 
> > task=ea744000 task.ti=ea7a6000)
> > Sep 11 00:39:34 zaratustra Stack: 00000000 000003e8 d9800000 0000389f 
> > c0119042 00000000 00000000 00000001
> > Sep 11 00:39:34 zaratustra 00000000 00000000 ea7a6f54 00010000 00000000 
> > c04d2e80 00000001 000e7ef0
> > Sep 11 00:39:34 zaratustra c01191a3 00000000 00000000 ea7a6fa0 00000001 
> > ffffffff c04d2e80 ea5b2480
> > Sep 11 00:39:34 zaratustra Call Trace:
> > Sep 11 00:39:34 zaratustra [<c0119042>] __rt_schedulable+0x52/0x130
> > Sep 11 00:39:34 zaratustra [<c01191a3>] sched_rt_handler+0x83/0x120
> > Sep 11 00:39:34 zaratustra [<c01a76a6>] proc_sys_call_handler+0xb6/0xd0
> > Sep 11 00:39:34 zaratustra [<c01a76c0>] proc_sys_write+0x0/0x20
> > Sep 11 00:39:34 zaratustra [<c01a76d9>] proc_sys_write+0x19/0x20
> > Sep 11 00:39:34 zaratustra [<c016cc68>] vfs_write+0xa8/0x140
> > Sep 11 00:39:34 zaratustra [<c016cdd1>] sys_write+0x41/0x80
> > Sep 11 00:39:34 zaratustra [<c0103051>] sysenter_past_esp+0x6a/0x91
> > Sep 11 00:39:34 zaratustra =======================
> > Sep 11 00:39:34 zaratustra Code: c8 41 0f ad f3 d3 ee f6 c1 20 0f 45 de 
> > 31 f6 0f ad ef d3 ed f6 c1 20 0f 45 fd 0f 45 ee 31 c9 39 eb 89 fe 89 ea 
> > 77 08 89 e8 31 d2 <f7> f3 89 c1 89 f0 8b 7c 24 08 f7 f3 8b 74 24 04 89 
> > ca 8b 1c 24
> > Sep 11 00:39:34 zaratustra EIP: [<c0213fc7>] div64_u64+0x57/0x80 SS:ESP 
> > 0068:ea7a6edc
> > Sep 11 00:39:34 zaratustra ---[ end trace 4eaa2a86a8e2da22 ]---
> 
> Hi,
> 
> I'm not sure this patch really addresses the issue.
> But the kernel locks after changing sysctl_sched_rt_period=0.
> 
> This patch is against -tip.
> I think it's needed to -stable too.
> -------->
> From: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>
> Subject: [PATCH] sched: do not allow sysctl_sched_rt_period=0
> 
> sysctl_sched_rt_period=0 makes exception at to_ratio().

Right - runtime can be -1, 0, +
but period ought to be >0, good spotting.

Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>

> Signed-off-by: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>
> ---
>  kernel/sched.c |    6 ++++++
>  1 files changed, 6 insertions(+), 0 deletions(-)
> 
> diff --git a/kernel/sched.c b/kernel/sched.c
> index 8f4af55..32d56d6 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -8971,6 +8971,9 @@ static int sched_rt_global_constraints(void)
>  	u64 rt_runtime, rt_period;
>  	int ret = 0;
>  
> +	if (sysctl_sched_rt_period <= 0)
> +		return -EINVAL;
> +
>  	rt_period = ktime_to_ns(tg->rt_bandwidth.rt_period);
>  	rt_runtime = tg->rt_bandwidth.rt_runtime;
>  
> @@ -8988,6 +8991,9 @@ static int sched_rt_global_constraints(void)
>  	unsigned long flags;
>  	int i;
>  
> +	if (sysctl_sched_rt_period <= 0)
> +		return -EINVAL;
> +
>  	spin_lock_irqsave(&def_rt_bandwidth.rt_runtime_lock, flags);
>  	for_each_possible_cpu(i) {
>  		struct rt_rq *rt_rq = &cpu_rq(i)->rt;