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From: Zhao Lei <zhaolei@cn.fujitsu.com>
To: "'Peter Zijlstra'" <peterz@infradead.org>,
        "'Anton Blanchard'" <anton@samba.org>
CC: "'Ingo Molnar'" <mingo@kernel.org>,
        "'Srikar Dronamraju'" <srikar@linux.vnet.ibm.com>,
        <tglx@linutronix.de>, <efault@gmx.de>, <htejun@gmail.com>,
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        <torvalds@linux-foundation.org>, <yangds.fnst@cn.fujitsu.com>,
        <hpa@zytor.com>, "'Stephen Rothwell'" <sfr@canb.auug.org.au>,
        "'Michael Ellerman'" <mpe@ellerman.id.au>
References: <aa171da036b520b51c79549e9b3215d29473f19d.1458635566.git.zhaolei@cn.fujitsu.com> <tip-d740037fac7052e49450f6fa1454f1144a103b55@git.kernel.org> <20160404140312.GA28495@linux.vnet.ibm.com> <20160406065436.GB3078@gmail.com> <20160406203219.788ae7cf@kryten> <20160406110803.GI2906@worktop>
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Subject: RE: [tip:sched/core] sched/cpuacct: Split usage accounting into user_usage and sys_usage
Date: Wed, 6 Apr 2016 19:43:53 +0800
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Hi, Anton and Peter

> -----Original Message-----
> From: Peter Zijlstra [mailto:peterz@infradead.org]
> Sent: Wednesday, April 06, 2016 7:08 PM
> To: Anton Blanchard <anton@samba.org>
> Cc: Ingo Molnar <mingo@kernel.org>; Srikar Dronamraju
> <srikar@linux.vnet.ibm.com>; tglx@linutronix.de; efault@gmx.de;
> htejun@gmail.com; linux-kernel@vger.kernel.org; tj@kernel.org;
> torvalds@linux-foundation.org; zhaolei@cn.fujitsu.com;
> yangds.fnst@cn.fujitsu.com; hpa@zytor.com; Stephen Rothwell
> <sfr@canb.auug.org.au>; Michael Ellerman <mpe@ellerman.id.au>
> Subject: Re: [tip:sched/core] sched/cpuacct: Split usage accounting into
> user_usage and sys_usage
> 
> On Wed, Apr 06, 2016 at 08:32:19PM +1000, Anton Blanchard wrote:
> > Hi,
> >
> > > > >  void cpuacct_charge(struct task_struct *tsk, u64 cputime)
> > > > >  {
> > > > >  	struct cpuacct *ca;
> > > > > +	int index;
> > > > > +
> > > > > +	if (user_mode(task_pt_regs(tsk)))
> > > > > +		index = CPUACCT_USAGE_USER;
> > > > > +	else
> > > > > +		index = CPUACCT_USAGE_SYSTEM;
> >
> > This is oopsing because PowerPC task_pt_regs() returns NULL for
> > kernel threads.
> 
Thanks for notice it.

> Ah, so sometihng like:
> 
> 	struct pt_regs *regs = task_pt_regs();
> 	int index = CPUACCT_USAGE_SYSTEM;
> 
> 	if (regs && user_mode(regs))
> 		index = CPUACCT_USAGE_USER;
> 
> should work, right?
> 
Thanks, I'll confirm it in a Power7 VM from buildroot.
(maybe need some hours or till tomorrow in a poor pc...)

Btw, I reproduced this bug in above vm.

Thanks
Zhaolei


>