Up to now, RCU has assumed that the CPU-online process makes it from
CPU_UP_PREPARE to set_cpu_online() within one jiffy. Given the recent
rise of virtualized environments, this assumption is very clearly
obsolete.
This commit therefore updates RCU's internal CPU state-tracking
information at notify_cpu_starting() time, thus providing exact
tracking of the CPU state from an RCU perspective.
Note that this means that incoming CPUs must not use RCU read-side
critical section (other than those of SRCU) until notify_cpu_starting()
time. Note that the CPU_STARTING notifiers -are- allowed to use
RCU read-side critical sections.
If a given architecture or CPU family needs to use RCU read-side critical
sections earlier, the call to rcu_cpu_starting() from notify_cpu_starting()
will need to be architecture-specific, with architectures that opt out
being required to hand-place the call to rcu_cpu_starting() at some point
preceding the call to notify_cpu_starting().
Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
---
include/linux/rcupdate.h | 1 +
kernel/cpu.c | 1 +
kernel/rcu/tree.c | 32 +++++++++++++++++++++++++++++---
3 files changed, 31 insertions(+), 3 deletions(-)
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 1aa62e1a761b..321f9ed552a9 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -334,6 +334,7 @@ void rcu_sched_qs(void);
void rcu_bh_qs(void);
void rcu_check_callbacks(int user);
void rcu_report_dead(unsigned int cpu);
+void rcu_cpu_starting(unsigned int cpu);
#ifndef CONFIG_TINY_RCU
void rcu_end_inkernel_boot(void);
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 341bf80f80bd..9482ceb928e0 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -889,6 +889,7 @@ void notify_cpu_starting(unsigned int cpu)
struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
enum cpuhp_state target = min((int)st->target, CPUHP_AP_ONLINE);
+ rcu_cpu_starting(cpu); /* All CPU_STARTING notifiers can use RCU. */
while (st->state < target) {
struct cpuhp_step *step;
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 5d80925e7fc8..d2973fb85e8c 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3792,8 +3792,6 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp)
rnp = rdp->mynode;
mask = rdp->grpmask;
raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
- rnp->qsmaskinitnext |= mask;
- rnp->expmaskinitnext |= mask;
if (!rdp->beenonline)
WRITE_ONCE(rsp->ncpus, READ_ONCE(rsp->ncpus) + 1);
rdp->beenonline = true; /* We have now been online. */
@@ -3860,6 +3858,32 @@ int rcutree_dead_cpu(unsigned int cpu)
return 0;
}
+/*
+ * Mark the specified CPU as being online so that subsequent grace periods
+ * (both expedited and normal) will wait on it. Note that this means that
+ * incoming CPUs are not allowed to use RCU read-side critical sections
+ * until this function is called. Failing to observe this restriction
+ * will result in lockdep splats.
+ */
+void rcu_cpu_starting(unsigned int cpu)
+{
+ unsigned long flags;
+ unsigned long mask;
+ struct rcu_data *rdp;
+ struct rcu_node *rnp;
+ struct rcu_state *rsp;
+
+ for_each_rcu_flavor(rsp) {
+ rdp = this_cpu_ptr(rsp->rda);
+ rnp = rdp->mynode;
+ mask = rdp->grpmask;
+ raw_spin_lock_irqsave_rcu_node(rnp, flags);
+ rnp->qsmaskinitnext |= mask;
+ rnp->expmaskinitnext |= mask;
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ }
+}
+
#ifdef CONFIG_HOTPLUG_CPU
/*
* The CPU is exiting the idle loop into the arch_cpu_idle_dead()
@@ -4209,8 +4233,10 @@ void __init rcu_init(void)
* or the scheduler are operational.
*/
pm_notifier(rcu_pm_notify, 0);
- for_each_online_cpu(cpu)
+ for_each_online_cpu(cpu) {
rcutree_prepare_cpu(cpu);
+ rcu_cpu_starting(cpu);
+ }
}
#include "tree_exp.h"
--
2.5.2
