Bulk CPU hotplug operations, such as an SMT switch operation, requires
hotplugging multiple CPUs. The current implementation takes
cpus_write_lock() for each individual CPU, causing multiple slow grace
period requests.
Introduce cpu_up_locked() and cpu_down_locked() that assume the caller
already holds cpus_write_lock(). The cpuhp_smt_enable() and
cpuhp_smt_disable() functions are updated to hold the lock once around
the entire loop, rather than for each individual CPU.
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Vishal Chourasia <vishalc@linux.ibm.com>
---
kernel/cpu.c | 73 ++++++++++++++++++++++++++++++++++++++--------------
1 file changed, 53 insertions(+), 20 deletions(-)
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 01968a5c4a16..edaa37419036 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1400,8 +1400,8 @@ static int cpuhp_down_callbacks(unsigned int cpu, struct cpuhp_cpu_state *st,
return ret;
}
-/* Requires cpu_add_remove_lock to be held */
-static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
+/* Requires cpu_add_remove_lock and cpus_write_lock to be held */
+static int __ref cpu_down_locked(unsigned int cpu, int tasks_frozen,
enum cpuhp_state target)
{
struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
@@ -1413,7 +1413,7 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
if (!cpu_present(cpu))
return -EINVAL;
- cpus_write_lock();
+ lockdep_assert_cpus_held();
/*
* Keep at least one housekeeping cpu onlined to avoid generating
@@ -1421,8 +1421,7 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
*/
if (cpumask_any_and(cpu_online_mask,
housekeeping_cpumask(HK_TYPE_DOMAIN)) >= nr_cpu_ids) {
- ret = -EBUSY;
- goto out;
+ return -EBUSY;
}
cpuhp_tasks_frozen = tasks_frozen;
@@ -1440,14 +1439,14 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
* return the error code..
*/
if (ret)
- goto out;
+ return ret;
/*
* We might have stopped still in the range of the AP hotplug
* thread. Nothing to do anymore.
*/
if (st->state > CPUHP_TEARDOWN_CPU)
- goto out;
+ return 0;
st->target = target;
}
@@ -1464,8 +1463,17 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
WARN(1, "DEAD callback error for CPU%d", cpu);
}
}
+ return ret;
+}
-out:
+static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
+ enum cpuhp_state target)
+{
+
+ int ret;
+
+ cpus_write_lock();
+ ret = cpu_down_locked(cpu, tasks_frozen, target);
cpus_write_unlock();
arch_smt_update();
return ret;
@@ -1613,18 +1621,18 @@ void cpuhp_online_idle(enum cpuhp_state state)
complete_ap_thread(st, true);
}
-/* Requires cpu_add_remove_lock to be held */
-static int _cpu_up(unsigned int cpu, int tasks_frozen, enum cpuhp_state target)
+/* Requires cpu_add_remove_lock and cpus_write_lock to be held. */
+static int cpu_up_locked(unsigned int cpu, int tasks_frozen,
+ enum cpuhp_state target)
{
struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
struct task_struct *idle;
int ret = 0;
- cpus_write_lock();
+ lockdep_assert_cpus_held();
if (!cpu_present(cpu)) {
- ret = -EINVAL;
- goto out;
+ return -EINVAL;
}
/*
@@ -1632,14 +1640,13 @@ static int _cpu_up(unsigned int cpu, int tasks_frozen, enum cpuhp_state target)
* caller. Nothing to do.
*/
if (st->state >= target)
- goto out;
+ return 0;
if (st->state == CPUHP_OFFLINE) {
/* Let it fail before we try to bring the cpu up */
idle = idle_thread_get(cpu);
if (IS_ERR(idle)) {
- ret = PTR_ERR(idle);
- goto out;
+ return PTR_ERR(idle);
}
/*
@@ -1663,7 +1670,7 @@ static int _cpu_up(unsigned int cpu, int tasks_frozen, enum cpuhp_state target)
* return the error code..
*/
if (ret)
- goto out;
+ return ret;
}
/*
@@ -1673,7 +1680,16 @@ static int _cpu_up(unsigned int cpu, int tasks_frozen, enum cpuhp_state target)
*/
target = min((int)target, CPUHP_BRINGUP_CPU);
ret = cpuhp_up_callbacks(cpu, st, target);
-out:
+ return ret;
+}
+
+/* Requires cpu_add_remove_lock to be held */
+static int _cpu_up(unsigned int cpu, int tasks_frozen, enum cpuhp_state target)
+{
+ int ret;
+
+ cpus_write_lock();
+ ret = cpu_up_locked(cpu, tasks_frozen, target);
cpus_write_unlock();
arch_smt_update();
return ret;
@@ -2659,6 +2675,16 @@ int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval)
int cpu, ret = 0;
cpu_maps_update_begin();
+ if (cpu_hotplug_offline_disabled) {
+ ret = -EOPNOTSUPP;
+ goto out;
+ }
+ if (cpu_hotplug_disabled) {
+ ret = -EBUSY;
+ goto out;
+ }
+ /* Hold cpus_write_lock() for entire batch operation. */
+ cpus_write_lock();
for_each_online_cpu(cpu) {
if (topology_is_primary_thread(cpu))
continue;
@@ -2668,7 +2694,7 @@ int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval)
*/
if (ctrlval == CPU_SMT_ENABLED && cpu_smt_thread_allowed(cpu))
continue;
- ret = cpu_down_maps_locked(cpu, CPUHP_OFFLINE);
+ ret = cpu_down_locked(cpu, 0, CPUHP_OFFLINE);
if (ret)
break;
/*
@@ -2688,6 +2714,9 @@ int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval)
}
if (!ret)
cpu_smt_control = ctrlval;
+ cpus_write_unlock();
+ arch_smt_update();
+out:
cpu_maps_update_done();
return ret;
}
@@ -2705,6 +2734,8 @@ int cpuhp_smt_enable(void)
int cpu, ret = 0;
cpu_maps_update_begin();
+ /* Hold cpus_write_lock() for entire batch operation. */
+ cpus_write_lock();
cpu_smt_control = CPU_SMT_ENABLED;
for_each_present_cpu(cpu) {
/* Skip online CPUs and CPUs on offline nodes */
@@ -2712,12 +2743,14 @@ int cpuhp_smt_enable(void)
continue;
if (!cpu_smt_thread_allowed(cpu) || !topology_is_core_online(cpu))
continue;
- ret = _cpu_up(cpu, 0, CPUHP_ONLINE);
+ ret = cpu_up_locked(cpu, 0, CPUHP_ONLINE);
if (ret)
break;
/* See comment in cpuhp_smt_disable() */
cpuhp_online_cpu_device(cpu);
}
+ cpus_write_unlock();
+ arch_smt_update();
cpu_maps_update_done();
return ret;
}
--
2.53.0
On 2/16/26 5:49 PM, Vishal Chourasia wrote:
> Bulk CPU hotplug operations, such as an SMT switch operation, requires
> hotplugging multiple CPUs. The current implementation takes
> cpus_write_lock() for each individual CPU, causing multiple slow grace
> period requests.
>
> Introduce cpu_up_locked() and cpu_down_locked() that assume the caller
> already holds cpus_write_lock(). The cpuhp_smt_enable() and
> cpuhp_smt_disable() functions are updated to hold the lock once around
> the entire loop, rather than for each individual CPU.
>
> Suggested-by: Peter Zijlstra <peterz@infradead.org>
> Signed-off-by: Vishal Chourasia <vishalc@linux.ibm.com>
> ---
> kernel/cpu.c | 73 ++++++++++++++++++++++++++++++++++++++--------------
> 1 file changed, 53 insertions(+), 20 deletions(-)
>
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index 01968a5c4a16..edaa37419036 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -1400,8 +1400,8 @@ static int cpuhp_down_callbacks(unsigned int cpu, struct cpuhp_cpu_state *st,
> return ret;
> }
>
> -/* Requires cpu_add_remove_lock to be held */
> -static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
> +/* Requires cpu_add_remove_lock and cpus_write_lock to be held */
> +static int __ref cpu_down_locked(unsigned int cpu, int tasks_frozen,
> enum cpuhp_state target)
> {
> struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
> @@ -1413,7 +1413,7 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
> if (!cpu_present(cpu))
> return -EINVAL;
>
> - cpus_write_lock();
> + lockdep_assert_cpus_held();
>
> /*
> * Keep at least one housekeeping cpu onlined to avoid generating
> @@ -1421,8 +1421,7 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
> */
> if (cpumask_any_and(cpu_online_mask,
> housekeeping_cpumask(HK_TYPE_DOMAIN)) >= nr_cpu_ids) {
> - ret = -EBUSY;
> - goto out;
> + return -EBUSY;
> }
>
> cpuhp_tasks_frozen = tasks_frozen;
> @@ -1440,14 +1439,14 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
> * return the error code..
> */
> if (ret)
> - goto out;
> + return ret;
>
> /*
> * We might have stopped still in the range of the AP hotplug
> * thread. Nothing to do anymore.
> */
> if (st->state > CPUHP_TEARDOWN_CPU)
> - goto out;
> + return 0;
>
> st->target = target;
> }
> @@ -1464,8 +1463,17 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
> WARN(1, "DEAD callback error for CPU%d", cpu);
> }
> }
> + return ret;
> +}
>
> -out:
> +static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
> + enum cpuhp_state target)
> +{
> +
Extra line isn't needed.
Please run checkpatch.pl --strict to fix some of these checks.
> + int ret;
> +
> + cpus_write_lock();
> + ret = cpu_down_locked(cpu, tasks_frozen, target);
> cpus_write_unlock();
> arch_smt_update();
> return ret;
> @@ -1613,18 +1621,18 @@ void cpuhp_online_idle(enum cpuhp_state state)
> complete_ap_thread(st, true);
> }
>
> -/* Requires cpu_add_remove_lock to be held */
> -static int _cpu_up(unsigned int cpu, int tasks_frozen, enum cpuhp_state target)
> +/* Requires cpu_add_remove_lock and cpus_write_lock to be held. */
> +static int cpu_up_locked(unsigned int cpu, int tasks_frozen,
> + enum cpuhp_state target)
> {
> struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
> struct task_struct *idle;
> int ret = 0;
>
> - cpus_write_lock();
> + lockdep_assert_cpus_held();
>
> if (!cpu_present(cpu)) {
> - ret = -EINVAL;
> - goto out;
> + return -EINVAL;
> }
>
> /*
> @@ -1632,14 +1640,13 @@ static int _cpu_up(unsigned int cpu, int tasks_frozen, enum cpuhp_state target)
> * caller. Nothing to do.
> */
> if (st->state >= target)
> - goto out;
> + return 0;
>
> if (st->state == CPUHP_OFFLINE) {
> /* Let it fail before we try to bring the cpu up */
> idle = idle_thread_get(cpu);
> if (IS_ERR(idle)) {
> - ret = PTR_ERR(idle);
> - goto out;
> + return PTR_ERR(idle);
> }
>
> /*
> @@ -1663,7 +1670,7 @@ static int _cpu_up(unsigned int cpu, int tasks_frozen, enum cpuhp_state target)
> * return the error code..
> */
> if (ret)
> - goto out;
> + return ret;
> }
>
> /*
> @@ -1673,7 +1680,16 @@ static int _cpu_up(unsigned int cpu, int tasks_frozen, enum cpuhp_state target)
> */
> target = min((int)target, CPUHP_BRINGUP_CPU);
> ret = cpuhp_up_callbacks(cpu, st, target);
> -out:
> + return ret;
> +}
> +
> +/* Requires cpu_add_remove_lock to be held */
> +static int _cpu_up(unsigned int cpu, int tasks_frozen, enum cpuhp_state target)
> +{
> + int ret;
> +
> + cpus_write_lock();
> + ret = cpu_up_locked(cpu, tasks_frozen, target);
> cpus_write_unlock();
> arch_smt_update();
> return ret;
> @@ -2659,6 +2675,16 @@ int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval)
> int cpu, ret = 0;
>
> cpu_maps_update_begin();
> + if (cpu_hotplug_offline_disabled) {
> + ret = -EOPNOTSUPP;
> + goto out;
> + }
> + if (cpu_hotplug_disabled) {
> + ret = -EBUSY;
> + goto out;
> + }
> + /* Hold cpus_write_lock() for entire batch operation. */
> + cpus_write_lock();
> for_each_online_cpu(cpu) {
> if (topology_is_primary_thread(cpu))
> continue;
> @@ -2668,7 +2694,7 @@ int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval)
> */
> if (ctrlval == CPU_SMT_ENABLED && cpu_smt_thread_allowed(cpu))
> continue;
> - ret = cpu_down_maps_locked(cpu, CPUHP_OFFLINE);
If you see comment in cpu_down_maps_locked, It says.
* Ensure that the control task does not run on the to be offlined
* CPU to prevent a deadlock against cfs_b->period_timer.
* Also keep at least one housekeeping cpu onlined to avoid generating
* an empty sched_domain span
Now, instead of running on the online_CPU you are now doing the _cpu_down
functionality in the cpu which is going offline.
How are you preventing that deadlock?
> + ret = cpu_down_locked(cpu, 0, CPUHP_OFFLINE);
> if (ret)
> break;
> /*
> @@ -2688,6 +2714,9 @@ int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval)
> }
> if (!ret)
> cpu_smt_control = ctrlval;
> + cpus_write_unlock();
> + arch_smt_update();
> +out:
> cpu_maps_update_done();
> return ret;
> }
> @@ -2705,6 +2734,8 @@ int cpuhp_smt_enable(void)
> int cpu, ret = 0;
>
> cpu_maps_update_begin();
> + /* Hold cpus_write_lock() for entire batch operation. */
> + cpus_write_lock();
> cpu_smt_control = CPU_SMT_ENABLED;
> for_each_present_cpu(cpu) {
> /* Skip online CPUs and CPUs on offline nodes */
> @@ -2712,12 +2743,14 @@ int cpuhp_smt_enable(void)
> continue;
> if (!cpu_smt_thread_allowed(cpu) || !topology_is_core_online(cpu))
> continue;
> - ret = _cpu_up(cpu, 0, CPUHP_ONLINE);
> + ret = cpu_up_locked(cpu, 0, CPUHP_ONLINE);
> if (ret)
> break;
> /* See comment in cpuhp_smt_disable() */
> cpuhp_online_cpu_device(cpu);
> }
> + cpus_write_unlock();
> + arch_smt_update();
> cpu_maps_update_done();
> return ret;
> }
On 2/16/26 6:27 PM, Shrikanth Hegde wrote:
>
>> */
>> if (ctrlval == CPU_SMT_ENABLED && cpu_smt_thread_allowed(cpu))
>> continue;
>> - ret = cpu_down_maps_locked(cpu, CPUHP_OFFLINE);
>
> If you see comment in cpu_down_maps_locked, It says.
>
> * Ensure that the control task does not run on the to be offlined
> * CPU to prevent a deadlock against cfs_b->period_timer.
> * Also keep at least one housekeeping cpu onlined to avoid
> generating
> * an empty sched_domain span
>
> Now, instead of running on the online_CPU you are now doing the _cpu_down
> functionality in the cpu which is going offline.
>
> How are you preventing that deadlock?
Ok. I should have looked at updated code. My bad.
This is no longer true after below commit.
de715325cc47 cpu: Revert "cpu/hotplug: Prevent self deadlock on CPU hot-unplug"
>
>> + ret = cpu_down_locked(cpu, 0, CPUHP_OFFLINE);
>> if (ret)
>> break;
>> /*
>> @@ -2688,6 +2714,9 @@ int cpuhp_smt_disable(enum cpuhp_smt_control
>> ctrlval)
>> }
>> if (!ret)
>> cpu_smt_control = ctrlval;
>> + cpus_write_unlock();
>> + arch_smt_update();
>> +out:
>> cpu_maps_update_done();
>> return ret;
>> }
>> @@ -2705,6 +2734,8 @@ int cpuhp_smt_enable(void)
>> int cpu, ret = 0;
>> cpu_maps_update_begin();
>> + /* Hold cpus_write_lock() for entire batch operation. */
>> + cpus_write_lock();
>> cpu_smt_control = CPU_SMT_ENABLED;
>> for_each_present_cpu(cpu) {
>> /* Skip online CPUs and CPUs on offline nodes */
>> @@ -2712,12 +2743,14 @@ int cpuhp_smt_enable(void)
>> continue;
>> if (!cpu_smt_thread_allowed(cpu) || !
>> topology_is_core_online(cpu))
>> continue;
>> - ret = _cpu_up(cpu, 0, CPUHP_ONLINE);
>> + ret = cpu_up_locked(cpu, 0, CPUHP_ONLINE);
>> if (ret)
>> break;
>> /* See comment in cpuhp_smt_disable() */
>> cpuhp_online_cpu_device(cpu);
>> }
>> + cpus_write_unlock();
>> + arch_smt_update();
>> cpu_maps_update_done();
>> return ret;
>> }
>
On Mon, Feb 16, 2026 at 05:49:28PM +0530, Vishal Chourasia wrote:
> Bulk CPU hotplug operations, such as an SMT switch operation, requires
> hotplugging multiple CPUs. The current implementation takes
> cpus_write_lock() for each individual CPU, causing multiple slow grace
> period requests.
>
> Introduce cpu_up_locked() and cpu_down_locked() that assume the caller
> already holds cpus_write_lock(). The cpuhp_smt_enable() and
> cpuhp_smt_disable() functions are updated to hold the lock once around
> the entire loop, rather than for each individual CPU.
>
> Suggested-by: Peter Zijlstra <peterz@infradead.org>
The code hositing the cpus_write_lock up in the cpuhp_smt_enable() was
provided by Joel [1]. Thanks Joel.
I missed adding an appropriate tag for it.
Originally-by: Joel Fernandes <joelagnelf@nvidia.com>
[1] https://lore.kernel.org/all/20260119051835.GA696111@joelbox2/
> Signed-off-by: Vishal Chourasia <vishalc@linux.ibm.com>
> ---
> kernel/cpu.c | 73 ++++++++++++++++++++++++++++++++++++++--------------
> 1 file changed, 53 insertions(+), 20 deletions(-)
>
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index 01968a5c4a16..edaa37419036 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -1400,8 +1400,8 @@ static int cpuhp_down_callbacks(unsigned int cpu, struct cpuhp_cpu_state *st,
> return ret;
> }
>
> -/* Requires cpu_add_remove_lock to be held */
> -static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
> +/* Requires cpu_add_remove_lock and cpus_write_lock to be held */
> +static int __ref cpu_down_locked(unsigned int cpu, int tasks_frozen,
> enum cpuhp_state target)
> {
> struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
> @@ -1413,7 +1413,7 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
> if (!cpu_present(cpu))
> return -EINVAL;
>
> - cpus_write_lock();
> + lockdep_assert_cpus_held();
>
> /*
> * Keep at least one housekeeping cpu onlined to avoid generating
> @@ -1421,8 +1421,7 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
> */
> if (cpumask_any_and(cpu_online_mask,
> housekeeping_cpumask(HK_TYPE_DOMAIN)) >= nr_cpu_ids) {
> - ret = -EBUSY;
> - goto out;
> + return -EBUSY;
> }
>
> cpuhp_tasks_frozen = tasks_frozen;
> @@ -1440,14 +1439,14 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
> * return the error code..
> */
> if (ret)
> - goto out;
> + return ret;
>
> /*
> * We might have stopped still in the range of the AP hotplug
> * thread. Nothing to do anymore.
> */
> if (st->state > CPUHP_TEARDOWN_CPU)
> - goto out;
> + return 0;
>
> st->target = target;
> }
> @@ -1464,8 +1463,17 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
> WARN(1, "DEAD callback error for CPU%d", cpu);
> }
> }
> + return ret;
> +}
>
> -out:
> +static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
> + enum cpuhp_state target)
> +{
> +
> + int ret;
> +
> + cpus_write_lock();
> + ret = cpu_down_locked(cpu, tasks_frozen, target);
> cpus_write_unlock();
> arch_smt_update();
> return ret;
> @@ -1613,18 +1621,18 @@ void cpuhp_online_idle(enum cpuhp_state state)
> complete_ap_thread(st, true);
> }
>
> -/* Requires cpu_add_remove_lock to be held */
> -static int _cpu_up(unsigned int cpu, int tasks_frozen, enum cpuhp_state target)
> +/* Requires cpu_add_remove_lock and cpus_write_lock to be held. */
> +static int cpu_up_locked(unsigned int cpu, int tasks_frozen,
> + enum cpuhp_state target)
> {
> struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
> struct task_struct *idle;
> int ret = 0;
>
> - cpus_write_lock();
> + lockdep_assert_cpus_held();
>
> if (!cpu_present(cpu)) {
> - ret = -EINVAL;
> - goto out;
> + return -EINVAL;
> }
>
> /*
> @@ -1632,14 +1640,13 @@ static int _cpu_up(unsigned int cpu, int tasks_frozen, enum cpuhp_state target)
> * caller. Nothing to do.
> */
> if (st->state >= target)
> - goto out;
> + return 0;
>
> if (st->state == CPUHP_OFFLINE) {
> /* Let it fail before we try to bring the cpu up */
> idle = idle_thread_get(cpu);
> if (IS_ERR(idle)) {
> - ret = PTR_ERR(idle);
> - goto out;
> + return PTR_ERR(idle);
> }
>
> /*
> @@ -1663,7 +1670,7 @@ static int _cpu_up(unsigned int cpu, int tasks_frozen, enum cpuhp_state target)
> * return the error code..
> */
> if (ret)
> - goto out;
> + return ret;
> }
>
> /*
> @@ -1673,7 +1680,16 @@ static int _cpu_up(unsigned int cpu, int tasks_frozen, enum cpuhp_state target)
> */
> target = min((int)target, CPUHP_BRINGUP_CPU);
> ret = cpuhp_up_callbacks(cpu, st, target);
> -out:
> + return ret;
> +}
> +
> +/* Requires cpu_add_remove_lock to be held */
> +static int _cpu_up(unsigned int cpu, int tasks_frozen, enum cpuhp_state target)
> +{
> + int ret;
> +
> + cpus_write_lock();
> + ret = cpu_up_locked(cpu, tasks_frozen, target);
> cpus_write_unlock();
> arch_smt_update();
> return ret;
> @@ -2659,6 +2675,16 @@ int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval)
> int cpu, ret = 0;
>
> cpu_maps_update_begin();
> + if (cpu_hotplug_offline_disabled) {
> + ret = -EOPNOTSUPP;
> + goto out;
> + }
> + if (cpu_hotplug_disabled) {
> + ret = -EBUSY;
> + goto out;
> + }
> + /* Hold cpus_write_lock() for entire batch operation. */
> + cpus_write_lock();
> for_each_online_cpu(cpu) {
> if (topology_is_primary_thread(cpu))
> continue;
> @@ -2668,7 +2694,7 @@ int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval)
> */
> if (ctrlval == CPU_SMT_ENABLED && cpu_smt_thread_allowed(cpu))
> continue;
> - ret = cpu_down_maps_locked(cpu, CPUHP_OFFLINE);
> + ret = cpu_down_locked(cpu, 0, CPUHP_OFFLINE);
> if (ret)
> break;
> /*
> @@ -2688,6 +2714,9 @@ int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval)
> }
> if (!ret)
> cpu_smt_control = ctrlval;
> + cpus_write_unlock();
> + arch_smt_update();
> +out:
> cpu_maps_update_done();
> return ret;
> }
> @@ -2705,6 +2734,8 @@ int cpuhp_smt_enable(void)
> int cpu, ret = 0;
>
> cpu_maps_update_begin();
> + /* Hold cpus_write_lock() for entire batch operation. */
> + cpus_write_lock();
> cpu_smt_control = CPU_SMT_ENABLED;
> for_each_present_cpu(cpu) {
> /* Skip online CPUs and CPUs on offline nodes */
> @@ -2712,12 +2743,14 @@ int cpuhp_smt_enable(void)
> continue;
> if (!cpu_smt_thread_allowed(cpu) || !topology_is_core_online(cpu))
> continue;
> - ret = _cpu_up(cpu, 0, CPUHP_ONLINE);
> + ret = cpu_up_locked(cpu, 0, CPUHP_ONLINE);
> if (ret)
> break;
> /* See comment in cpuhp_smt_disable() */
> cpuhp_online_cpu_device(cpu);
> }
> + cpus_write_unlock();
> + arch_smt_update();
> cpu_maps_update_done();
> return ret;
> }
> --
> 2.53.0
>
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