linux-kernel - [PATCH tip/core/urgent] rcu: rcu_read_lock_bh

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Date:	Wed, 22 Sep 2010 17:32:20 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
	josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, eric.dumazet@...il.com
Subject: [PATCH tip/core/urgent] rcu: rcu_read_lock_bh_held(): disabling
 irqs also disables bh

rcu_dereference_bh() doesnt know yet about hard irq being disabled, so
lockdep can trigger in netpoll_rx() after commit f0f9deae9e7c4 (netpoll:
Disable IRQ around RCU dereference in netpoll_rx)

Reported-by: Miles Lane <miles.lane@...il.com>
Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
Tested-by: Miles Lane <miles.lane@...il.com>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 include/linux/rcupdate.h |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 9fbc54a..0dcc00e 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -454,7 +454,8 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
  * Makes rcu_dereference_check() do the dirty work.
  */
 #define rcu_dereference_bh(p) \
-		rcu_dereference_check(p, rcu_read_lock_bh_held())
+		rcu_dereference_check(p, rcu_read_lock_bh_held() || \
+					 irqs_disabled())
 
 /**
  * rcu_dereference_sched - fetch RCU-protected pointer, checking for RCU-sched
-- 
1.7.0.6

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