rcu: Simplify offline processing

Move ->qsmaskinit and blkd_tasks[] manipulation to the CPU_DYING
notifier.  This simplifies the code by eliminating a potential
deadlock and by reducing the responsibilities of force_quiescent_state().
Also rename functions to make their connection to the CPU-hotplug
stages explicit.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2012-01-07 11:03:57 -08:00 committed by Paul E. McKenney
parent ae1f18e480
commit e560140008
3 changed files with 88 additions and 97 deletions

View File

@ -943,6 +943,10 @@ rcu_start_gp_per_cpu(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_dat
* in preparation for detecting the next grace period. The caller must hold
* the root node's ->lock, which is released before return. Hard irqs must
* be disabled.
*
* Note that it is legal for a dying CPU (which is marked as offline) to
* invoke this function. This can happen when the dying CPU reports its
* quiescent state.
*/
static void
rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
@ -1245,118 +1249,101 @@ rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp)
/*
* Move a dying CPU's RCU callbacks to online CPU's callback list.
* Synchronization is not required because this function executes
* in stop_machine() context.
* Also record a quiescent state for this CPU for the current grace period.
* Synchronization and interrupt disabling are not required because
* this function executes in stop_machine() context. Therefore, cleanup
* operations that might block must be done later from the CPU_DEAD
* notifier.
*
* Note that the outgoing CPU's bit has already been cleared in the
* cpu_online_mask. This allows us to randomly pick a callback
* destination from the bits set in that mask.
*/
static void rcu_send_cbs_to_online(struct rcu_state *rsp)
static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
{
unsigned long flags;
int i;
/* current DYING CPU is cleared in the cpu_online_mask */
unsigned long mask;
int need_report;
int receive_cpu = cpumask_any(cpu_online_mask);
struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
struct rcu_data *receive_rdp = per_cpu_ptr(rsp->rda, receive_cpu);
struct rcu_node *rnp = rdp->mynode; /* For dying CPU. */
if (rdp->nxtlist == NULL)
return; /* irqs disabled, so comparison is stable. */
/* Move callbacks to some other CPU. */
if (rdp->nxtlist != NULL) {
*receive_rdp->nxttail[RCU_NEXT_TAIL] = rdp->nxtlist;
receive_rdp->nxttail[RCU_NEXT_TAIL] =
rdp->nxttail[RCU_NEXT_TAIL];
receive_rdp->qlen_lazy += rdp->qlen_lazy;
receive_rdp->qlen += rdp->qlen;
receive_rdp->n_cbs_adopted += rdp->qlen;
rdp->n_cbs_orphaned += rdp->qlen;
*receive_rdp->nxttail[RCU_NEXT_TAIL] = rdp->nxtlist;
receive_rdp->nxttail[RCU_NEXT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
receive_rdp->qlen_lazy += rdp->qlen_lazy;
receive_rdp->qlen += rdp->qlen;
receive_rdp->n_cbs_adopted += rdp->qlen;
rdp->n_cbs_orphaned += rdp->qlen;
rdp->nxtlist = NULL;
for (i = 0; i < RCU_NEXT_SIZE; i++)
rdp->nxttail[i] = &rdp->nxtlist;
rdp->qlen_lazy = 0;
rdp->qlen = 0;
}
rdp->nxtlist = NULL;
for (i = 0; i < RCU_NEXT_SIZE; i++)
rdp->nxttail[i] = &rdp->nxtlist;
rdp->qlen_lazy = 0;
rdp->qlen = 0;
}
/*
* Remove the outgoing CPU from the bitmasks in the rcu_node hierarchy
* and move all callbacks from the outgoing CPU to the current one.
* There can only be one CPU hotplug operation at a time, so no other
* CPU can be attempting to update rcu_cpu_kthread_task.
*/
static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
{
unsigned long flags;
unsigned long mask;
int need_report = 0;
struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
struct rcu_node *rnp;
rcu_stop_cpu_kthread(cpu);
/* Exclude any attempts to start a new grace period. */
raw_spin_lock_irqsave(&rsp->onofflock, flags);
/* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */
rnp = rdp->mynode; /* this is the outgoing CPU's rnp. */
/* Record a quiescent state for the dying CPU. */
mask = rdp->grpmask; /* rnp->grplo is constant. */
trace_rcu_grace_period(rsp->name,
rnp->gpnum + 1 - !!(rnp->qsmask & mask),
"cpuofl");
rcu_report_qs_rdp(smp_processor_id(), rsp, rdp, rsp->gpnum);
/* Note that rcu_report_qs_rdp() might call trace_rcu_grace_period(). */
/*
* Remove the dying CPU from the bitmasks in the rcu_node
* hierarchy. Because we are in stop_machine() context, we
* automatically exclude ->onofflock critical sections.
*/
do {
raw_spin_lock(&rnp->lock); /* irqs already disabled. */
raw_spin_lock_irqsave(&rnp->lock, flags);
rnp->qsmaskinit &= ~mask;
if (rnp->qsmaskinit != 0) {
if (rnp != rdp->mynode)
raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
else
trace_rcu_grace_period(rsp->name,
rnp->gpnum + 1 -
!!(rnp->qsmask & mask),
"cpuofl");
raw_spin_unlock_irqrestore(&rnp->lock, flags);
break;
}
if (rnp == rdp->mynode) {
trace_rcu_grace_period(rsp->name,
rnp->gpnum + 1 -
!!(rnp->qsmask & mask),
"cpuofl");
need_report = rcu_preempt_offline_tasks(rsp, rnp, rdp);
if (need_report & RCU_OFL_TASKS_NORM_GP)
rcu_report_unblock_qs_rnp(rnp, flags);
else
raw_spin_unlock_irqrestore(&rnp->lock, flags);
if (need_report & RCU_OFL_TASKS_EXP_GP)
rcu_report_exp_rnp(rsp, rnp, true);
} else
raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
raw_spin_unlock_irqrestore(&rnp->lock, flags);
mask = rnp->grpmask;
rnp = rnp->parent;
} while (rnp != NULL);
/*
* We still hold the leaf rcu_node structure lock here, and
* irqs are still disabled. The reason for this subterfuge is
* because invoking rcu_report_unblock_qs_rnp() with ->onofflock
* held leads to deadlock.
*/
raw_spin_unlock(&rsp->onofflock); /* irqs remain disabled. */
rnp = rdp->mynode;
if (need_report & RCU_OFL_TASKS_NORM_GP)
rcu_report_unblock_qs_rnp(rnp, flags);
else
raw_spin_unlock_irqrestore(&rnp->lock, flags);
if (need_report & RCU_OFL_TASKS_EXP_GP)
rcu_report_exp_rnp(rsp, rnp, true);
rcu_node_kthread_setaffinity(rnp, -1);
}
/*
* Remove the specified CPU from the RCU hierarchy and move any pending
* callbacks that it might have to the current CPU. This code assumes
* that at least one CPU in the system will remain running at all times.
* Any attempt to offline -all- CPUs is likely to strand RCU callbacks.
* The CPU has been completely removed, and some other CPU is reporting
* this fact from process context. Do the remainder of the cleanup.
* There can only be one CPU hotplug operation at a time, so no other
* CPU can be attempting to update rcu_cpu_kthread_task.
*/
static void rcu_offline_cpu(int cpu)
static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
{
__rcu_offline_cpu(cpu, &rcu_sched_state);
__rcu_offline_cpu(cpu, &rcu_bh_state);
rcu_preempt_offline_cpu(cpu);
struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
struct rcu_node *rnp = rdp->mynode;
rcu_stop_cpu_kthread(cpu);
rcu_node_kthread_setaffinity(rnp, -1);
}
#else /* #ifdef CONFIG_HOTPLUG_CPU */
static void rcu_send_cbs_to_online(struct rcu_state *rsp)
static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
{
}
static void rcu_offline_cpu(int cpu)
static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
{
}
@ -1725,6 +1712,7 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
* a quiescent state betweentimes.
*/
local_irq_save(flags);
WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
rdp = this_cpu_ptr(rsp->rda);
/* Add the callback to our list. */
@ -2155,16 +2143,18 @@ static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
* touch any data without introducing corruption. We send the
* dying CPU's callbacks to an arbitrarily chosen online CPU.
*/
rcu_send_cbs_to_online(&rcu_bh_state);
rcu_send_cbs_to_online(&rcu_sched_state);
rcu_preempt_send_cbs_to_online();
rcu_cleanup_dying_cpu(&rcu_bh_state);
rcu_cleanup_dying_cpu(&rcu_sched_state);
rcu_preempt_cleanup_dying_cpu();
rcu_cleanup_after_idle(cpu);
break;
case CPU_DEAD:
case CPU_DEAD_FROZEN:
case CPU_UP_CANCELED:
case CPU_UP_CANCELED_FROZEN:
rcu_offline_cpu(cpu);
rcu_cleanup_dead_cpu(cpu, &rcu_bh_state);
rcu_cleanup_dead_cpu(cpu, &rcu_sched_state);
rcu_preempt_cleanup_dead_cpu(cpu);
break;
default:
break;

View File

@ -439,8 +439,8 @@ static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp);
static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
struct rcu_node *rnp,
struct rcu_data *rdp);
static void rcu_preempt_offline_cpu(int cpu);
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
static void rcu_preempt_cleanup_dead_cpu(int cpu);
static void rcu_preempt_check_callbacks(int cpu);
static void rcu_preempt_process_callbacks(void);
void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu));
@ -451,7 +451,7 @@ static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
static int rcu_preempt_pending(int cpu);
static int rcu_preempt_needs_cpu(int cpu);
static void __cpuinit rcu_preempt_init_percpu_data(int cpu);
static void rcu_preempt_send_cbs_to_online(void);
static void rcu_preempt_cleanup_dying_cpu(void);
static void __init __rcu_init_preempt(void);
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags);
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp);

View File

@ -618,16 +618,16 @@ static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
return retval;
}
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
/*
* Do CPU-offline processing for preemptible RCU.
*/
static void rcu_preempt_offline_cpu(int cpu)
static void rcu_preempt_cleanup_dead_cpu(int cpu)
{
__rcu_offline_cpu(cpu, &rcu_preempt_state);
rcu_cleanup_dead_cpu(cpu, &rcu_preempt_state);
}
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
/*
* Check for a quiescent state from the current CPU. When a task blocks,
* the task is recorded in the corresponding CPU's rcu_node structure,
@ -912,11 +912,12 @@ static void __cpuinit rcu_preempt_init_percpu_data(int cpu)
}
/*
* Move preemptible RCU's callbacks from dying CPU to other online CPU.
* Move preemptible RCU's callbacks from dying CPU to other online CPU
* and record a quiescent state.
*/
static void rcu_preempt_send_cbs_to_online(void)
static void rcu_preempt_cleanup_dying_cpu(void)
{
rcu_send_cbs_to_online(&rcu_preempt_state);
rcu_cleanup_dying_cpu(&rcu_preempt_state);
}
/*
@ -1052,16 +1053,16 @@ static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
return 0;
}
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
/*
* Because preemptible RCU does not exist, it never needs CPU-offline
* processing.
*/
static void rcu_preempt_offline_cpu(int cpu)
static void rcu_preempt_cleanup_dead_cpu(int cpu)
{
}
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
/*
* Because preemptible RCU does not exist, it never has any callbacks
* to check.
@ -1153,9 +1154,9 @@ static void __cpuinit rcu_preempt_init_percpu_data(int cpu)
}
/*
* Because there is no preemptible RCU, there are no callbacks to move.
* Because there is no preemptible RCU, there is no cleanup to do.
*/
static void rcu_preempt_send_cbs_to_online(void)
static void rcu_preempt_cleanup_dying_cpu(void)
{
}