Preempt-RCU: Fix rcu_barrier for preemptive environment.
From: Paul E. McKenney <[email protected]>
Fix rcu_barrier() to work properly in preemptive kernel environment.
Also, the ordering of callback must be preserved while moving
callbacks to another CPU during CPU hotplug.
Signed-off-by: Gautham R Shenoy <[email protected]>
Signed-off-by: Dipankar Sarma <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
---
kernel/rcuclassic.c | 2 +-
kernel/rcupdate.c | 10 ++++++++++
2 files changed, 11 insertions(+), 1 deletions(-)
diff --git a/kernel/rcuclassic.c b/kernel/rcuclassic.c
index 11c16aa..deb2acc 100644
--- a/kernel/rcuclassic.c
+++ b/kernel/rcuclassic.c
@@ -371,9 +371,9 @@ static void __rcu_offline_cpu(struct rcu_data *this_rdp,
if (rcp->cur != rcp->completed)
cpu_quiet(rdp->cpu, rcp);
spin_unlock_bh(&rcp->lock);
+ rcu_move_batch(this_rdp, rdp->donelist, rdp->donetail);
rcu_move_batch(this_rdp, rdp->curlist, rdp->curtail);
rcu_move_batch(this_rdp, rdp->nxtlist, rdp->nxttail);
- rcu_move_batch(this_rdp, rdp->donelist, rdp->donetail);
}
static void rcu_offline_cpu(int cpu)
diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index 0ccd009..760dfc2 100644
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -115,7 +115,17 @@ void rcu_barrier(void)
mutex_lock(&rcu_barrier_mutex);
init_completion(&rcu_barrier_completion);
atomic_set(&rcu_barrier_cpu_count, 0);
+ /*
+ * The queueing of callbacks in all CPUs must be atomic with
+ * respect to RCU, otherwise one CPU may queue a callback,
+ * wait for a grace period, decrement barrier count and call
+ * complete(), while other CPUs have not yet queued anything.
+ * So, we need to make sure that grace periods cannot complete
+ * until all the callbacks are queued.
+ */
+ rcu_read_lock();
on_each_cpu(rcu_barrier_func, NULL, 0, 1);
+ rcu_read_unlock();
wait_for_completion(&rcu_barrier_completion);
mutex_unlock(&rcu_barrier_mutex);
}
--
Gautham R Shenoy
Linux Technology Center
IBM India.
"Freedom comes with a price tag of responsibility, which is still a bargain,
because Freedom is priceless!"
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