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Date: Wed, 7 Sep 2016 08:50:57 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Stanislaw Gruszka <sgruszka@redhat.com>
Cc: linux-kernel@vger.kernel.org,
        Giovanni Gherdovich <ggherdovich@suse.cz>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Mel Gorman <mgorman@techsingularity.net>,
        Mike Galbraith <mgalbraith@suse.de>,
        Paolo Bonzini <pbonzini@redhat.com>, Rik van Riel <riel@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Wanpeng Li <wanpeng.li@hotmail.com>, Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH v3] sched/cputime: Protect some other sum_exec_runtime
 reads on 32 bit cpus
Message-ID: <20160907065057.GM10168@twins.programming.kicks-ass.net>
References: <1473166148-8466-1-git-send-email-sgruszka@redhat.com>
 <20160906190129.GO10153@twins.programming.kicks-ass.net>
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On Tue, Sep 06, 2016 at 09:01:29PM +0200, Peter Zijlstra wrote:
> > diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
> > index 39008d7..a2d753b 100644
> > --- a/kernel/time/posix-cpu-timers.c
> > +++ b/kernel/time/posix-cpu-timers.c
> > @@ -848,7 +848,7 @@ static void check_thread_timers(struct task_struct *tsk,
> >  	tsk_expires->virt_exp = expires_to_cputime(expires);
> >  
> >  	tsk_expires->sched_exp = check_timers_list(++timers, firing,
> > -						   tsk->se.sum_exec_runtime);
> > +						   read_sum_exec_runtime(tsk));
> >  
> >  	/*
> >  	 * Check for the special case thread timers.
> 
> @tsk == current and IRQs are disabled, sum_exec_runtime cannot be
> updated.
> 
> > @@ -1115,7 +1115,7 @@ static inline int fastpath_timer_check(struct task_struct *tsk)
> >  		struct task_cputime task_sample;
> >  
> >  		task_cputime(tsk, &task_sample.utime, &task_sample.stime);
> > -		task_sample.sum_exec_runtime = tsk->se.sum_exec_runtime;
> > +		task_sample.sum_exec_runtime = read_sum_exec_runtime(tsk);
> >  		if (task_cputime_expired(&task_sample, &tsk->cputime_expires))
> >  			return 1;
> >  	}
> 
> Same.

Sorry, I forgot syscalls, those can muck with update_curr() remotely. So
yes, those are needed.