On Tue, Jan 22, 2013 at 01:05:10PM +0530, Srivatsa S. Bhat wrote:
> Once stop_machine() is gone from the CPU offline path, we won't be able to
> depend on preempt_disable() to prevent CPUs from going offline from under us.
>
> Use the get/put_online_cpus_atomic() APIs to prevent CPUs from going offline,
> while invoking from atomic context.
>
> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>
Would it make sense for get_online_cpus_atomic() to return the current
CPU number? Looks good otherwise.
Thanx, Paul
> ---
>
> kernel/smp.c | 40 ++++++++++++++++++++++++++--------------
> 1 file changed, 26 insertions(+), 14 deletions(-)
>
> diff --git a/kernel/smp.c b/kernel/smp.c
> index 29dd40a..f421bcc 100644
> --- a/kernel/smp.c
> +++ b/kernel/smp.c
> @@ -310,7 +310,8 @@ int smp_call_function_single(int cpu, smp_call_func_t func, void *info,
> * prevent preemption and reschedule on another processor,
> * as well as CPU removal
> */
> - this_cpu = get_cpu();
> + get_online_cpus_atomic();
> + this_cpu = smp_processor_id();
>
> /*
> * Can deadlock when called with interrupts disabled.
> @@ -342,7 +343,7 @@ int smp_call_function_single(int cpu, smp_call_func_t func, void *info,
> }
> }
>
> - put_cpu();
> + put_online_cpus_atomic();
>
> return err;
> }
> @@ -371,8 +372,10 @@ int smp_call_function_any(const struct cpumask *mask,
> const struct cpumask *nodemask;
> int ret;
>
> + get_online_cpus_atomic();
> /* Try for same CPU (cheapest) */
> - cpu = get_cpu();
> + cpu = smp_processor_id();
> +
> if (cpumask_test_cpu(cpu, mask))
> goto call;
>
> @@ -388,7 +391,7 @@ int smp_call_function_any(const struct cpumask *mask,
> cpu = cpumask_any_and(mask, cpu_online_mask);
> call:
> ret = smp_call_function_single(cpu, func, info, wait);
> - put_cpu();
> + put_online_cpus_atomic();
> return ret;
> }
> EXPORT_SYMBOL_GPL(smp_call_function_any);
> @@ -409,25 +412,28 @@ void __smp_call_function_single(int cpu, struct call_single_data *data,
> unsigned int this_cpu;
> unsigned long flags;
>
> - this_cpu = get_cpu();
> + get_online_cpus_atomic();
> +
> + this_cpu = smp_processor_id();
> +
> /*
> * Can deadlock when called with interrupts disabled.
> * We allow cpu's that are not yet online though, as no one else can
> * send smp call function interrupt to this cpu and as such deadlocks
> * can't happen.
> */
> - WARN_ON_ONCE(cpu_online(smp_processor_id()) && wait && irqs_disabled()
> + WARN_ON_ONCE(cpu_online(this_cpu) && wait && irqs_disabled()
> && !oops_in_progress);
>
> if (cpu == this_cpu) {
> local_irq_save(flags);
> data->func(data->info);
> local_irq_restore(flags);
> - } else {
> + } else if ((unsigned)cpu < nr_cpu_ids && cpu_online(cpu)) {
> csd_lock(data);
> generic_exec_single(cpu, data, wait);
> }
> - put_cpu();
> + put_online_cpus_atomic();
> }
>
> /**
> @@ -451,6 +457,8 @@ void smp_call_function_many(const struct cpumask *mask,
> unsigned long flags;
> int refs, cpu, next_cpu, this_cpu = smp_processor_id();
>
> + get_online_cpus_atomic();
> +
> /*
> * Can deadlock when called with interrupts disabled.
> * We allow cpu's that are not yet online though, as no one else can
> @@ -467,17 +475,18 @@ void smp_call_function_many(const struct cpumask *mask,
>
> /* No online cpus? We're done. */
> if (cpu >= nr_cpu_ids)
> - return;
> + goto out_unlock;
>
> /* Do we have another CPU which isn't us? */
> next_cpu = cpumask_next_and(cpu, mask, cpu_online_mask);
> if (next_cpu == this_cpu)
> - next_cpu = cpumask_next_and(next_cpu, mask, cpu_online_mask);
> + next_cpu = cpumask_next_and(next_cpu, mask,
> + cpu_online_mask);
>
> /* Fastpath: do that cpu by itself. */
> if (next_cpu >= nr_cpu_ids) {
> smp_call_function_single(cpu, func, info, wait);
> - return;
> + goto out_unlock;
> }
>
> data = &__get_cpu_var(cfd_data);
> @@ -523,7 +532,7 @@ void smp_call_function_many(const struct cpumask *mask,
> /* Some callers race with other cpus changing the passed mask */
> if (unlikely(!refs)) {
> csd_unlock(&data->csd);
> - return;
> + goto out_unlock;
> }
>
> raw_spin_lock_irqsave(&call_function.lock, flags);
> @@ -554,6 +563,9 @@ void smp_call_function_many(const struct cpumask *mask,
> /* Optionally wait for the CPUs to complete */
> if (wait)
> csd_lock_wait(&data->csd);
> +
> +out_unlock:
> + put_online_cpus_atomic();
> }
> EXPORT_SYMBOL(smp_call_function_many);
>
> @@ -574,9 +586,9 @@ EXPORT_SYMBOL(smp_call_function_many);
> */
> int smp_call_function(smp_call_func_t func, void *info, int wait)
> {
> - preempt_disable();
> + get_online_cpus_atomic();
> smp_call_function_many(cpu_online_mask, func, info, wait);
> - preempt_enable();
> + put_online_cpus_atomic();
>
> return 0;
> }
>
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