1 files changed, 49 insertions, 3 deletions

diff --git a/kernel/rcuclassic.c b/kernel/rcuclassic.c
index f4ffbd0f306f..16eeeaa9d618 100644
--- a/kernel/rcuclassic.c
+++ b/kernel/rcuclassic.c
@@ -89,8 +89,22 @@ static void force_quiescent_state(struct rcu_data *rdp,
                 /*
                  * Don't send IPI to itself. With irqs disabled,
                  * rdp->cpu is the current cpu.
+                 *
+                 * cpu_online_map is updated by the _cpu_down()
+                 * using stop_machine_run(). Since we're in irqs disabled
+                 * section, stop_machine_run() is not exectuting, hence
+                 * the cpu_online_map is stable.
+                 *
+                 * However,  a cpu might have been offlined _just_ before
+                 * we disabled irqs while entering here.
+                 * And rcu subsystem might not yet have handled the CPU_DEAD
+                 * notification, leading to the offlined cpu's bit
+                 * being set in the rcp->cpumask.
+                 *
+                 * Hence cpumask = (rcp->cpumask & cpu_online_map) to prevent
+                 * sending smp_reschedule() to an offlined CPU.
                  */
-                cpumask = rcp->cpumask;
+                cpus_and(cpumask, rcp->cpumask, cpu_online_map);
                 cpu_clear(rdp->cpu, cpumask);
                 for_each_cpu_mask(cpu, cpumask)
                         smp_send_reschedule(cpu);
@@ -373,6 +387,10 @@ static void __rcu_offline_cpu(struct rcu_data *this_rdp,
         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);
+
+        local_irq_disable();
+        this_rdp->qlen += rdp->qlen;
+        local_irq_enable();
 }
 
 static void rcu_offline_cpu(int cpu)
@@ -502,10 +520,38 @@ void rcu_check_callbacks(int cpu, int user)
         if (user ||
             (idle_cpu(cpu) && !in_softirq() &&
                                 hardirq_count() <= (1 << HARDIRQ_SHIFT))) {
+
+                /*
+                 * Get here if this CPU took its interrupt from user
+                 * mode or from the idle loop, and if this is not a
+                 * nested interrupt.  In this case, the CPU is in
+                 * a quiescent state, so count it.
+                 *
+                 * Also do a memory barrier.  This is needed to handle
+                 * the case where writes from a preempt-disable section
+                 * of code get reordered into schedule() by this CPU's
+                 * write buffer.  The memory barrier makes sure that
+                 * the rcu_qsctr_inc() and rcu_bh_qsctr_inc() are see
+                 * by other CPUs to happen after any such write.
+                 */
+
+                smp_mb();  /* See above block comment. */
                 rcu_qsctr_inc(cpu);
                 rcu_bh_qsctr_inc(cpu);
-        } else if (!in_softirq())
+
+        } else if (!in_softirq()) {
+
+                /*
+                 * Get here if this CPU did not take its interrupt from
+                 * softirq, in other words, if it is not interrupting
+                 * a rcu_bh read-side critical section.  This is an _bh
+                 * critical section, so count it.  The memory barrier
+                 * is needed for the same reason as is the above one.
+                 */
+
+                smp_mb();  /* See above block comment. */
                 rcu_bh_qsctr_inc(cpu);
+        }
         raise_rcu_softirq();
 }
 
@@ -529,7 +575,7 @@ static void __cpuinit rcu_online_cpu(int cpu)
 
         rcu_init_percpu_data(cpu, &rcu_ctrlblk, rdp);
         rcu_init_percpu_data(cpu, &rcu_bh_ctrlblk, bh_rdp);
-        open_softirq(RCU_SOFTIRQ, rcu_process_callbacks, NULL);
+        open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
 }
 
 static int __cpuinit rcu_cpu_notify(struct notifier_block *self,