[PATCH 2/5] rcu: don't check ->donelist in __rcu_pending()

From: Oleg Nesterov <oleg@tv-sign.ru>
To: linux-kernel@vger.kernel.org
Cc: Dipankar Sarma <dipankar@in.ibm.com>,
	Manfred Spraul <manfred@colorfullife.com>,
	Linus Torvalds <torvalds@osdl.org>,
	"Paul E. McKenney" <paulmck@us.ibm.com>,
	Andrew Morton <akpm@osdl.org>
Subject: [PATCH 2/5] rcu: don't check ->donelist in __rcu_pending()
Date: Sun, 08 Jan 2006 22:19:24 +0300	[thread overview]
Message-ID: <43C165BC.F7C6DCF5@tv-sign.ru> (raw)

->donelist becomes != NULL only in rcu_process_callbacks().

rcu_process_callbacks() always calls rcu_do_batch() when
->donelist != NULL.

rcu_do_batch() schedules rcu_process_callbacks() again if
->donelist was not flushed entirely.

So ->donelist != NULL means that rcu_tasklet is either
TASKLET_STATE_SCHED or TASKLET_STATE_RUN, we don't need to
check it in __rcu_pending().

[ This patch was tested with rcutorture.ko, I don't understand
  it's output, but it says "End of test: SUCCESS". So if this
  patch incorrect blame Paul, not me! ]

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>

--- 2.6.15/kernel/rcupdate.c~2_DONE	2006-01-08 21:35:21.000000000 +0300
+++ 2.6.15/kernel/rcupdate.c	2006-01-08 21:55:45.000000000 +0300
@@ -454,10 +454,6 @@ static int __rcu_pending(struct rcu_ctrl
 	if (!rdp->curlist && rdp->nxtlist)
 		return 1;
 
-	/* This cpu has finished callbacks to invoke */
-	if (rdp->donelist)
-		return 1;
-
 	/* The rcu core waits for a quiescent state from the cpu */
 	if (rdp->quiescbatch != rcp->cur || rdp->qs_pending)
 		return 1;
