[PATCH] rcu_do_batch: make ->qlen decrement irq safe

rcu_do_batch() decrements rdp->qlen with irqs enabled.  This is not good,
it can also be modified by call_rcu() from interrupt.

Decrement ->qlen once with irqs disabled, after a main loop.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Dipankar Sarma <dipankar@in.ibm.com>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 5 insertions, 1 deletions

diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index 436ab35f6fa..523e46483b9 100644
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -241,12 +241,16 @@ static void rcu_do_batch(struct rcu_data *rdp)
                 next = rdp->donelist = list->next;
                 list->func(list);
                 list = next;
-                rdp->qlen--;
                 if (++count >= rdp->blimit)
                         break;
         }
+
+        local_irq_disable();
+        rdp->qlen -= count;
+        local_irq_enable();
         if (rdp->blimit == INT_MAX && rdp->qlen <= qlowmark)
                 rdp->blimit = blimit;
+
         if (!rdp->donelist)
                 rdp->donetail = &rdp->donelist;
         else