On Fri, 20 Dec 2013 18:13:43 +0100
Peter Zijlstra <[email protected]> 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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