| Message ID | 20130122073508.13822.12784.stgit@srivatsabhat.in.ibm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
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@linux.vnet.ibm.com> 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; > } >
On 02/09/2013 05:37 AM, Paul E. McKenney wrote: > 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@linux.vnet.ibm.com> > > Would it make sense for get_online_cpus_atomic() to return the current > CPU number? Hmm, I'm not so sure. I tried to model it after get_online_cpus(), which doesn't return anything (for other reasons, of course..) Moreover, a function name like *_cpu_* returning the CPU number would be intuitive. But a name such as *_cpus_* (plural) returning a CPU number might appear confusing.. And also I don't think it'll make a huge improvement in the callers.. (We might be better off avoiding an smp_processor_id() if possible, since this function could be called in very hot paths).. So I don't see a strong case for returning the CPU number. But let me know if you think it'll still be worth it for some reason... > Looks good otherwise. > Thank you very much for the detailed review, Paul! Regards, Srivatsa S. Bhat > >> --- >> >> 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; >> } >>
On Mon, Feb 11, 2013 at 01:11:29AM +0530, Srivatsa S. Bhat wrote: > On 02/09/2013 05:37 AM, Paul E. McKenney wrote: > > 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@linux.vnet.ibm.com> > > > > Would it make sense for get_online_cpus_atomic() to return the current > > CPU number? > > Hmm, I'm not so sure. I tried to model it after get_online_cpus(), which doesn't > return anything (for other reasons, of course..) > > Moreover, a function name like *_cpu_* returning the CPU number would be intuitive. > But a name such as *_cpus_* (plural) returning a CPU number might appear confusing.. > > And also I don't think it'll make a huge improvement in the callers.. (We might > be better off avoiding an smp_processor_id() if possible, since this function could > be called in very hot paths).. So I don't see a strong case for returning the > CPU number. But let me know if you think it'll still be worth it for some reason... I just noted a lot of two-line code sequences in your patch that would be one line if the CPU number was returned. But I don't feel strongly about it, so if people are OK with the current version, no problem. Thanx, Paul > > Looks good otherwise. > > > > Thank you very much for the detailed review, Paul! > > Regards, > Srivatsa S. Bhat > > > > >> --- > >> > >> 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; > >> } > >> >
On 02/11/2013 01:26 AM, Paul E. McKenney wrote: > On Mon, Feb 11, 2013 at 01:11:29AM +0530, Srivatsa S. Bhat wrote: >> On 02/09/2013 05:37 AM, Paul E. McKenney wrote: >>> 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@linux.vnet.ibm.com> >>> >>> Would it make sense for get_online_cpus_atomic() to return the current >>> CPU number? >> >> Hmm, I'm not so sure. I tried to model it after get_online_cpus(), which doesn't >> return anything (for other reasons, of course..) >> >> Moreover, a function name like *_cpu_* returning the CPU number would be intuitive. >> But a name such as *_cpus_* (plural) returning a CPU number might appear confusing.. >> >> And also I don't think it'll make a huge improvement in the callers.. (We might >> be better off avoiding an smp_processor_id() if possible, since this function could >> be called in very hot paths).. So I don't see a strong case for returning the >> CPU number. But let me know if you think it'll still be worth it for some reason... > > I just noted a lot of two-line code sequences in your patch that would be > one line if the CPU number was returned. Ah, in that case, I'll reconsider your suggestion while working on the next version. Thanks! Regards, Srivatsa S. Bhat > But I don't feel strongly about > it, so if people are OK with the current version, no problem. > > Thanx, Paul >
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; }
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@linux.vnet.ibm.com> --- kernel/smp.c | 40 ++++++++++++++++++++++++++-------------- 1 file changed, 26 insertions(+), 14 deletions(-)