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rcu: Make TASKS_RCU handle nohz_full= CPUs

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Currently TASKS_RCU would ignore a CPU running a task in nohz_full=
usermode execution.  There would be neither a context switch nor a
scheduling-clock interrupt to tell TASKS_RCU that the task in question
had passed through a quiescent state.  The grace period would therefore
extend indefinitely.  This commit therefore makes RCU's dyntick-idle
subsystem record the task_struct structure of the task that is running
in dyntick-idle mode on each CPU.  The TASKS_RCU grace period can
then access this information and record a quiescent state on
behalf of any CPU running in dyntick-idle usermode.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2014-08-04 17:43:50 -07:00
parent 84a8f446ff
commit 176f8f7a52
6 changed files with 27 additions and 2 deletions
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3
include/linux/init_task.h
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@ -121,7 +121,8 @@ extern struct group_info init_groups;
#define INIT_TASK_RCU_TASKS(tsk) \
.rcu_tasks_holdout = false, \
.rcu_tasks_holdout_list = \
LIST_HEAD_INIT(tsk.rcu_tasks_holdout_list),
LIST_HEAD_INIT(tsk.rcu_tasks_holdout_list), \
.rcu_tasks_idle_cpu = -1,
#else
#define INIT_TASK_RCU_TASKS(tsk)
#endif

2
include/linux/sched.h
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@ -1274,6 +1274,7 @@ struct task_struct {
unsigned long rcu_tasks_nvcsw;
bool rcu_tasks_holdout;
struct list_head rcu_tasks_holdout_list;
int rcu_tasks_idle_cpu;
#endif /* #ifdef CONFIG_TASKS_RCU */
#if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
@ -2020,6 +2021,7 @@ static inline void rcu_copy_process(struct task_struct *p)
#ifdef CONFIG_TASKS_RCU
p->rcu_tasks_holdout = false;
INIT_LIST_HEAD(&p->rcu_tasks_holdout_list);
p->rcu_tasks_idle_cpu = -1;
#endif /* #ifdef CONFIG_TASKS_RCU */
}

2
kernel/rcu/tree.c
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@ -526,6 +526,7 @@ static void rcu_eqs_enter_common(struct rcu_dynticks *rdtp, long long oldval,
atomic_inc(&rdtp->dynticks);
smp_mb__after_atomic(); /* Force ordering with next sojourn. */
WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
rcu_dynticks_task_enter();
/*
* It is illegal to enter an extended quiescent state while
@ -642,6 +643,7 @@ void rcu_irq_exit(void)
static void rcu_eqs_exit_common(struct rcu_dynticks *rdtp, long long oldval,
int user)
{
rcu_dynticks_task_exit();
smp_mb__before_atomic(); /* Force ordering w/previous sojourn. */
atomic_inc(&rdtp->dynticks);
/* CPUs seeing atomic_inc() must see later RCU read-side crit sects */

2
kernel/rcu/tree.h
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@ -605,6 +605,8 @@ static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle,
static void rcu_bind_gp_kthread(void);
static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp);
static bool rcu_nohz_full_cpu(struct rcu_state *rsp);
static void rcu_dynticks_task_enter(void);
static void rcu_dynticks_task_exit(void);
#endif /* #ifndef RCU_TREE_NONCORE */

16
kernel/rcu/tree_plugin.h
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@ -3036,3 +3036,19 @@ static void rcu_bind_gp_kthread(void)
housekeeping_affine(current);
#endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
}
/* Record the current task on dyntick-idle entry. */
static void rcu_dynticks_task_enter(void)
{
#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
ACCESS_ONCE(current->rcu_tasks_idle_cpu) = smp_processor_id();
#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
}
/* Record no current task on dyntick-idle exit. */
static void rcu_dynticks_task_exit(void)
{
#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
ACCESS_ONCE(current->rcu_tasks_idle_cpu) = -1;
#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
}

4
kernel/rcu/update.c
View File

@ -463,7 +463,9 @@ static void check_holdout_task(struct task_struct *t,
{
if (!ACCESS_ONCE(t->rcu_tasks_holdout) ||
t->rcu_tasks_nvcsw != ACCESS_ONCE(t->nvcsw) ||
!ACCESS_ONCE(t->on_rq)) {
!ACCESS_ONCE(t->on_rq) ||
(IS_ENABLED(CONFIG_NO_HZ_FULL) &&
!is_idle_task(t) && t->rcu_tasks_idle_cpu >= 0)) {
ACCESS_ONCE(t->rcu_tasks_holdout) = false;
list_del_rcu(&t->rcu_tasks_holdout_list);
put_task_struct(t);