Messages in this thread | | | Date | Fri, 20 Dec 2013 12:37:07 -0500 | From | Steven Rostedt <> | Subject | Re: [PATCH 09/13] sched: Add bandwidth management for sched_dl |
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On Fri, 20 Dec 2013 18:13:43 +0100 Peter Zijlstra <peterz@infradead.org> wrote:
> @@ -4985,6 +4942,23 @@ migration_call(struct notifier_block *nf > unsigned long flags; > struct rq *rq = cpu_rq(cpu); > > + switch (action) { > + case CPU_DOWN_PREPARE: /* explicitly allow suspend */ > + { > + struct dl_bw *dl_b = dl_bw_of(cpu); > + int cpus = dl_bw_cpus(cpu); > + bool overflow; > + > + raw_spin_lock_irqsave(&dl_b->lock, flags); > + overflow = __dl_overflow(dl_b, cpus-1, 0, 0); > + raw_spin_unlock_irqrestore(&dl_b->lock, flags); > + > + if (overflow) > + return notifier_from_errno(-EBUSY);
Is it possible to have a race here to create a new deadline task that may work with cpus but not cpus-1? That is, if a new deadline task is currently being created as a CPU is going offline, this check happens first while the creation is spinning on the dl_b->lock, and it sets overflow to false, then once the lock is released, the new deadline task makes the condition true.
Should the system call have a get_online_cpus() somewhere?
-- Steve
> + } > + break; > + } > + > switch (action & ~CPU_TASKS_FROZEN) { > > case CPU_UP_PREPARE:
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