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: Dipankar Sarma <[email protected]>
---
diff -puN kernel/rcuclassic.c~rcu-fix-barriers kernel/rcuclassic.c
--- linux-2.6.20-rc3-mm1-rcu/kernel/rcuclassic.c~rcu-fix-barriers 2007-01-15 15:36:47.000000000 +0530
+++ linux-2.6.20-rc3-mm1-rcu-dipankar/kernel/rcuclassic.c 2007-01-15 15:36:47.000000000 +0530
@@ -350,9 +350,9 @@ static void __rcu_offline_cpu(struct rcu
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 -puN kernel/rcupdate.c~rcu-fix-barriers kernel/rcupdate.c
--- linux-2.6.20-rc3-mm1-rcu/kernel/rcupdate.c~rcu-fix-barriers 2007-01-15 15:36:47.000000000 +0530
+++ linux-2.6.20-rc3-mm1-rcu-dipankar/kernel/rcupdate.c 2007-01-15 15:36:47.000000000 +0530
@@ -117,7 +117,18 @@ 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
+ * haven't yet queued anything. So, we need to make sure
+ * that no grace period happens 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);
}
_
-
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