linux-kernel - [PATCH -tip] rcu: fix lockdep for tracepoint

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Message-ID: <4B9F48AD.4000404@cn.fujitsu.com>
Date:	Tue, 16 Mar 2010 17:00:29 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Ingo Molnar <mingo@...e.hu>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH -tip] rcu: fix lockdep for tracepoint

tracepoint.h use rcu_dereference(), it triggers this warning:

[    0.701161] ===================================================
[    0.702211] [ INFO: suspicious rcu_dereference_check() usage. ]
[    0.702716] ---------------------------------------------------
[    0.703203] include/trace/events/workqueue.h:68 invoked rcu_dereference_check() without protection!
[    0.703971]
[    0.703990] other info that might help us debug this:
[    0.703993]
[    0.705590]
[    0.705604] rcu_scheduler_active = 1, debug_locks = 0
[    0.706712] 1 lock held by swapper/1:
[    0.707229]  #0:  (cpu_add_remove_lock){+.+.+.}, at: [<c0142f54>] cpu_maps_update_begin+0x14/0x20
[    0.710097]
[    0.710106] stack backtrace:
[    0.712602] Pid: 1, comm: swapper Not tainted 2.6.34-rc1-tip-01613-g72662bb #168
[    0.713231] Call Trace:
[    0.713997]  [<c017174d>] lockdep_rcu_dereference+0x9d/0xb0
[    0.714746]  [<c015a117>] create_workqueue_thread+0x107/0x110
[    0.715353]  [<c015aee0>] ? worker_thread+0x0/0x340
[    0.715845]  [<c015a8e8>] __create_workqueue_key+0x138/0x240
[    0.716427]  [<c0142f92>] ? cpu_maps_update_done+0x12/0x20
[    0.717012]  [<c086b12f>] init_workqueues+0x6f/0x80
[    0.717530]  [<c08576d2>] kernel_init+0x102/0x1f0
[    0.717570]  [<c08575d0>] ? kernel_init+0x0/0x1f0
[    0.718944]  [<c01030fa>] kernel_thread_helper+0x6/0x10

Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
---
diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index f59604e..78b4bd3 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -49,7 +49,7 @@ struct tracepoint {
 		void **it_func;						\
 									\
 		rcu_read_lock_sched_notrace();				\
-		it_func = rcu_dereference((tp)->funcs);			\
+		it_func = rcu_dereference_sched((tp)->funcs);		\
 		if (it_func) {						\
 			do {						\
 				((void(*)(proto))(*it_func))(args);	\

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