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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2016-06-30 13:58:26 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2016-08-22 09:36:57 -0700
commit7ec99de36f402618ae44147ac7fa9a07e4757a5f (patch)
tree47d88c0cca429331ec1d20e89435fa5fefda972c /kernel/rcu
parent29b4817d4018df78086157ea3a55c1d9424a7cfc (diff)
downloadlinux-7ec99de36f402618ae44147ac7fa9a07e4757a5f.tar.bz2
rcu: Provide exact CPU-online tracking for RCU
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. Failing to meet this deadline can result in RCU paying attention to an incoming CPU for one jiffy, then ignoring it until the grace period following the one in which that CPU sets itself online. This situation might prove to be fatally disappointing to any RCU read-side critical sections that had the misfortune to execute during the time in which RCU was ignoring the slow-to-come-online CPU. This commit therefore updates RCU's internal CPU state-tracking information at notify_cpu_starting() time, thus providing RCU with an exact transition of the CPU's state from offline to online. 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 also that the CPU_STARTING notifiers -are- allowed to use RCU read-side critical sections. (Of course, CPU-hotplug notifiers are rapidly becoming obsolete, so you need to act fast!) 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 need early use 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 <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'kernel/rcu')
-rw-r--r--kernel/rcu/tree.c32
1 files changed, 29 insertions, 3 deletions
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"