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sched/rt: Add missing rmb()
While discussing the proposed SCHED_DEADLINE patches which in parts mimic the existing FIFO code it was noticed that the wmb in rt_set_overloaded() didn't have a matching barrier. The only site using rt_overloaded() to test the rto_count is pull_rt_task() and we should issue a matching rmb before then assuming there's an rto_mask bit set. Without that smp_rmb() in there we could actually miss seeing the rto_mask bit. Also, change to using smp_[wr]mb(), even though this is SMP only code; memory barriers without smp_ always make me think they're against hardware of some sort. Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: vincent.guittot@linaro.org Cc: luca.abeni@unitn.it Cc: bruce.ashfield@windriver.com Cc: dhaval.giani@gmail.com Cc: rostedt@goodmis.org Cc: hgu1972@gmail.com Cc: oleg@redhat.com Cc: fweisbec@gmail.com Cc: darren@dvhart.com Cc: johan.eker@ericsson.com Cc: p.faure@akatech.ch Cc: paulmck@linux.vnet.ibm.com Cc: raistlin@linux.it Cc: claudio@evidence.eu.com Cc: insop.song@gmail.com Cc: michael@amarulasolutions.com Cc: liming.wang@windriver.com Cc: fchecconi@gmail.com Cc: jkacur@redhat.com Cc: tommaso.cucinotta@sssup.it Cc: Juri Lelli <juri.lelli@gmail.com> Cc: harald.gustafsson@ericsson.com Cc: nicola.manica@disi.unitn.it Cc: tglx@linutronix.de Link: http://lkml.kernel.org/r/20131015103507.GF10651@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar <mingo@kernel.org>
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1 changed files with 9 additions and 1 deletions
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@ -246,8 +246,10 @@ static inline void rt_set_overload(struct rq *rq)
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* if we should look at the mask. It would be a shame
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* if we looked at the mask, but the mask was not
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* updated yet.
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*
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* Matched by the barrier in pull_rt_task().
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*/
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wmb();
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smp_wmb();
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atomic_inc(&rq->rd->rto_count);
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}
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@ -1626,6 +1628,12 @@ static int pull_rt_task(struct rq *this_rq)
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if (likely(!rt_overloaded(this_rq)))
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return 0;
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/*
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* Match the barrier from rt_set_overloaded; this guarantees that if we
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* see overloaded we must also see the rto_mask bit.
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*/
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smp_rmb();
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for_each_cpu(cpu, this_rq->rd->rto_mask) {
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if (this_cpu == cpu)
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continue;
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