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Date: Tue, 16 Jul 2019 00:07:43 -0400
From: "Joel Fernandes (Google)" <joel@...lfernandes.org>
To: linux-kernel@...r.kernel.org
Cc: "Joel Fernandes (Google)" <joel@...lfernandes.org>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
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	Borislav Petkov <bp@...en8.de>,
	c0d1n61at3@...il.com,
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	edumazet@...gle.com,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	"H. Peter Anvin" <hpa@...or.com>,
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	will@...nel.org,
	x86@...nel.org (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT))
Subject: [PATCH] rculist: Add build check for single optional list argument

In a previous patch series [1], we added an optional lockdep expression
argument to list_for_each_entry_rcu() and the hlist equivalent. This
also meant more than one optional argument can be passed to them with
that error going unnoticed. To fix this, let us force a compiler error
more than one optional argument is passed.

[1] https://lore.kernel.org/patchwork/project/lkml/list/?series=402150

Suggested-by: Paul McKenney <paulmck@...ux.vnet.ibm.com>
Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
---
 include/linux/rculist.h | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index 1048160625bb..86659f6d72dc 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -44,14 +44,18 @@ static inline void INIT_LIST_HEAD_RCU(struct list_head *list)
  * Check during list traversal that we are within an RCU reader
  */
 
+#define check_arg_count_one(dummy)
+
 #ifdef CONFIG_PROVE_RCU_LIST
-#define __list_check_rcu(dummy, cond, ...)				\
+#define __list_check_rcu(dummy, cond, extra...)				\
 	({								\
+	check_arg_count_one(extra);					\
 	RCU_LOCKDEP_WARN(!cond && !rcu_read_lock_any_held(),		\
 			 "RCU-list traversed in non-reader section!");	\
 	 })
 #else
-#define __list_check_rcu(dummy, cond, ...) ({})
+#define __list_check_rcu(dummy, cond, extra...)				\
+	({ check_arg_count_one(extra); })
 #endif
 
 /*
-- 
2.22.0.510.g264f2c817a-goog

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