Messages in this thread Patch in this message |  | | Date | Thu, 17 Oct 2013 09:49:20 -0700 | From | tip-bot for Peter Zijlstra <> | Subject | [tip:sched/core] sched/rt: Add missing rmb() |
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Commit-ID: 7c3f2ab7b844f1a859afbc3d41925e8a0faba5fa Gitweb: http://git.kernel.org/tip/7c3f2ab7b844f1a859afbc3d41925e8a0faba5fa Author: Peter Zijlstra <peterz@infradead.org> AuthorDate: Tue, 15 Oct 2013 12:35:07 +0200 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Wed, 16 Oct 2013 14:22:13 +0200
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> --- kernel/sched/rt.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c index e9304cd..a848f52 100644 --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -246,8 +246,10 @@ static inline void rt_set_overload(struct rq *rq) * if we should look at the mask. It would be a shame * if we looked at the mask, but the mask was not * updated yet. + * + * Matched by the barrier in pull_rt_task(). */ - wmb(); + smp_wmb(); atomic_inc(&rq->rd->rto_count); } @@ -1626,6 +1628,12 @@ static int pull_rt_task(struct rq *this_rq) if (likely(!rt_overloaded(this_rq))) return 0; + /* + * Match the barrier from rt_set_overloaded; this guarantees that if we + * see overloaded we must also see the rto_mask bit. + */ + smp_rmb(); + for_each_cpu(cpu, this_rq->rd->rto_mask) { if (this_cpu == cpu) continue;
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