Merge branch 'core/rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

* 'core/rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip: (23 commits)
  rcu classic: update qlen when cpu offline
  rcu: make rcutorture even more vicious: invoke RCU readers from irq handlers (timers)
  rcu: make quiescent rcutorture less power-hungry
  rcu, rcutorture: make quiescent rcutorture less power-hungry
  rcu: make rcutorture more vicious: reinstate boot-time testing
  rcu: make rcutorture more vicious: add stutter feature
  rcutorture: WARN_ON_ONCE(1) when detecting an error
  rcu: remove unused field struct rcu_data::rcu_tasklet
  Revert "prohibit rcutorture from being compiled into the kernel"
  rcu: fix nf_conntrack_helper.c build bug
  rculist.h: fix include in net/netfilter/nf_conntrack_netlink.c
  rcu: remove duplicated include in kernel/rcupreempt.c
  rcu: remove duplicated include in kernel/rcupreempt_trace.c
  RCU, rculist.h: fix list iterators
  rcu: fix rcu_try_flip_waitack_needed() to prevent grace-period stall
  rculist.h: use the rcu API
  rcu: split list.h and move rcu-protected lists into rculist.h
  sched: 1Q08 RCU doc update, add call_rcu_sched()
  rcu: add call_rcu_sched() and friends to rcutorture
  rcu: add rcu_barrier_sched() and rcu_barrier_bh()
  ...

1 files changed, 33 insertions, 1 deletions

diff --git a/kernel/rcuclassic.c b/kernel/rcuclassic.c
index 65c0906080ef..16eeeaa9d618 100644
--- a/kernel/rcuclassic.c
+++ b/kernel/rcuclassic.c
@@ -387,6 +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)
@@ -516,10 +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();
 }