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Date: Wed, 6 Apr 2016 13:08:03 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Anton Blanchard <anton@samba.org>
Cc: Ingo Molnar <mingo@kernel.org>,
        Srikar Dronamraju <srikar@linux.vnet.ibm.com>, tglx@linutronix.de,
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        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
Message-ID: <20160406110803.GI2906@worktop>
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>
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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.

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?