When the RCU Tasks scanning on-rq tasks, there is no need to scanning
tasks which record on dyntick-idle entry, at this time, these tasks are
not remain within an RCU Tasks read-side critical section.
This commit skip scanning tasks which record on dyntick-idle entry in
rcu_tasks_pertask().
Reported-by: kernel test robot <[email protected]>
Signed-off-by: Zqiang <[email protected]>
---
v1->v2:
fix build test ERROR due to CONFIG_TASKS_RCU=n
kernel/rcu/tasks.h | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)
diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index f6459343e4b6..7cb0f922478e 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -809,10 +809,17 @@ static void rcu_tasks_pregp_step(struct list_head *hop)
synchronize_rcu();
}
+static bool task_is_on_dyntick_idle(struct task_struct *t)
+{
+ return IS_ENABLED(CONFIG_NO_HZ_FULL) && !is_idle_task(t) &&
+ t->rcu_tasks_idle_cpu >= 0;
+}
+
/* Per-task initial processing. */
static void rcu_tasks_pertask(struct task_struct *t, struct list_head *hop)
{
- if (t != current && READ_ONCE(t->on_rq) && !is_idle_task(t)) {
+ if (t != current && READ_ONCE(t->on_rq) && !is_idle_task(t) &&
+ !task_is_on_dyntick_idle(t)) {
get_task_struct(t);
t->rcu_tasks_nvcsw = READ_ONCE(t->nvcsw);
WRITE_ONCE(t->rcu_tasks_holdout, true);
@@ -842,8 +849,7 @@ static void check_holdout_task(struct task_struct *t,
if (!READ_ONCE(t->rcu_tasks_holdout) ||
t->rcu_tasks_nvcsw != READ_ONCE(t->nvcsw) ||
!READ_ONCE(t->on_rq) ||
- (IS_ENABLED(CONFIG_NO_HZ_FULL) &&
- !is_idle_task(t) && t->rcu_tasks_idle_cpu >= 0)) {
+ task_is_on_dyntick_idle(t)) {
WRITE_ONCE(t->rcu_tasks_holdout, false);
list_del_init(&t->rcu_tasks_holdout_list);
put_task_struct(t);
--
2.25.1
On Fri, May 20, 2022 at 04:41:55PM +0800, Zqiang wrote:
> When the RCU Tasks scanning on-rq tasks, there is no need to scanning
> tasks which record on dyntick-idle entry, at this time, these tasks are
> not remain within an RCU Tasks read-side critical section.
>
> This commit skip scanning tasks which record on dyntick-idle entry in
> rcu_tasks_pertask().
>
> Reported-by: kernel test robot <[email protected]>
> Signed-off-by: Zqiang <[email protected]>
You lost me with this one. Doesn't the rcu_tasks_pertask() function
already exclude the idle tasks that might possibly be running in
dyntick-idle state in non-CONFIG_NO_HZ_FULL systems?
What am I missing here?
Thanx, Paul
> ---
> v1->v2:
> fix build test ERROR due to CONFIG_TASKS_RCU=n
>
> kernel/rcu/tasks.h | 12 +++++++++---
> 1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
> index f6459343e4b6..7cb0f922478e 100644
> --- a/kernel/rcu/tasks.h
> +++ b/kernel/rcu/tasks.h
> @@ -809,10 +809,17 @@ static void rcu_tasks_pregp_step(struct list_head *hop)
> synchronize_rcu();
> }
>
> +static bool task_is_on_dyntick_idle(struct task_struct *t)
> +{
> + return IS_ENABLED(CONFIG_NO_HZ_FULL) && !is_idle_task(t) &&
> + t->rcu_tasks_idle_cpu >= 0;
> +}
> +
> /* Per-task initial processing. */
> static void rcu_tasks_pertask(struct task_struct *t, struct list_head *hop)
> {
> - if (t != current && READ_ONCE(t->on_rq) && !is_idle_task(t)) {
> + if (t != current && READ_ONCE(t->on_rq) && !is_idle_task(t) &&
> + !task_is_on_dyntick_idle(t)) {
> get_task_struct(t);
> t->rcu_tasks_nvcsw = READ_ONCE(t->nvcsw);
> WRITE_ONCE(t->rcu_tasks_holdout, true);
> @@ -842,8 +849,7 @@ static void check_holdout_task(struct task_struct *t,
> if (!READ_ONCE(t->rcu_tasks_holdout) ||
> t->rcu_tasks_nvcsw != READ_ONCE(t->nvcsw) ||
> !READ_ONCE(t->on_rq) ||
> - (IS_ENABLED(CONFIG_NO_HZ_FULL) &&
> - !is_idle_task(t) && t->rcu_tasks_idle_cpu >= 0)) {
> + task_is_on_dyntick_idle(t)) {
> WRITE_ONCE(t->rcu_tasks_holdout, false);
> list_del_init(&t->rcu_tasks_holdout_list);
> put_task_struct(t);
> --
> 2.25.1
>
On Fri, May 20, 2022 at 04:41:55PM +0800, Zqiang wrote:
> When the RCU Tasks scanning on-rq tasks, there is no need to scanning
> tasks which record on dyntick-idle entry, at this time, these tasks
> are not remain within an RCU Tasks read-side critical section.
>
> This commit skip scanning tasks which record on dyntick-idle entry in
> rcu_tasks_pertask().
>
> Reported-by: kernel test robot <[email protected]>
> Signed-off-by: Zqiang <[email protected]>
>
>You lost me with this one. Doesn't the rcu_tasks_pertask() function already exclude the idle tasks that might possibly be running in dyntick-idle state in non-CONFIG_NO_HZ_FULL systems?
>
>What am I missing here?
Thanks for reply.
Yes, the is_idle_task() can remove from task_is_on_dyntick_idle().
And the is_idle_task() can also remove from warnings in check_holdout_task(), because
the rcu _tasks_pertask() already exclude the idle tasks. Is my understanding correct?
Thanks
Zqiang
> Thanx, Paul
>
> ---
> v1->v2:
> fix build test ERROR due to CONFIG_TASKS_RCU=n
>
> kernel/rcu/tasks.h | 12 +++++++++---
> 1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index
> f6459343e4b6..7cb0f922478e 100644
> --- a/kernel/rcu/tasks.h
> +++ b/kernel/rcu/tasks.h
> @@ -809,10 +809,17 @@ static void rcu_tasks_pregp_step(struct list_head *hop)
> synchronize_rcu();
> }
>
> +static bool task_is_on_dyntick_idle(struct task_struct *t) {
> + return IS_ENABLED(CONFIG_NO_HZ_FULL) && !is_idle_task(t) &&
> + t->rcu_tasks_idle_cpu >= 0;
> +}
> +
> /* Per-task initial processing. */
> static void rcu_tasks_pertask(struct task_struct *t, struct list_head
> *hop) {
> - if (t != current && READ_ONCE(t->on_rq) && !is_idle_task(t)) {
> + if (t != current && READ_ONCE(t->on_rq) && !is_idle_task(t) &&
> + !task_is_on_dyntick_idle(t)) {
> get_task_struct(t);
> t->rcu_tasks_nvcsw = READ_ONCE(t->nvcsw);
> WRITE_ONCE(t->rcu_tasks_holdout, true); @@ -842,8 +849,7 @@ static
> void check_holdout_task(struct task_struct *t,
> if (!READ_ONCE(t->rcu_tasks_holdout) ||
> t->rcu_tasks_nvcsw != READ_ONCE(t->nvcsw) ||
> !READ_ONCE(t->on_rq) ||
> - (IS_ENABLED(CONFIG_NO_HZ_FULL) &&
> - !is_idle_task(t) && t->rcu_tasks_idle_cpu >= 0)) {
> + task_is_on_dyntick_idle(t)) {
> WRITE_ONCE(t->rcu_tasks_holdout, false);
> list_del_init(&t->rcu_tasks_holdout_list);
> put_task_struct(t);
> --
> 2.25.1
>