[PATCH] rcu_process_callbacks: don't cli() while testing ->nxtlist

__rcu_process_callbacks() disables interrupts to protect itself from
call_rcu() which adds new entries to ->nxtlist.

However we can check "->nxtlist != NULL" with interrupts enabled, we can't
get "false positives" because call_rcu() can only change this condition
from 0 to 1.

Tested with rcutorture.ko.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: 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, 2 insertions, 3 deletions

diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index 6df1559b1c02..13458bbaa1be 100644
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -416,8 +416,8 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp,
                 rdp->curtail = &rdp->curlist;
         }
 
-        local_irq_disable();
         if (rdp->nxtlist && !rdp->curlist) {
+                local_irq_disable();
                 rdp->curlist = rdp->nxtlist;
                 rdp->curtail = rdp->nxttail;
                 rdp->nxtlist = NULL;
@@ -442,9 +442,8 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp,
                         rcu_start_batch(rcp);
                         spin_unlock(&rcp->lock);
                 }
-        } else {
-                local_irq_enable();
         }
+
         rcu_check_quiescent_state(rcp, rdp);
         if (rdp->donelist)
                 rcu_do_batch(rdp);