linux-kernel - [PATCH] rcu: change _wait_rcu_gp() to work around gcc 67055 bug

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Message-ID: <20150825184518.GA15234@redhat.com>
Date:	Tue, 25 Aug 2015 20:45:18 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Mark Salter <msalter@...hat.com>,
	Yoshinori Sato <ysato@...rs.sourceforge.jp>,
	uclinux-h8-devel@...ts.sourceforge.jp,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Peter Zijlstra (Intel)" <peterz@...radead.org>,
	Josh Triplett <josh@...htriplett.org>,
	Guenter Roeck <linux@...ck-us.net>
Subject: [PATCH] rcu: change _wait_rcu_gp() to work around gcc 67055 bug

The code like

	const int n = const-expr;
	whatever_t array[n];

in inline function can confuse gcc, see

	https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67055#c13

This leads to

	In file included from include/linux/rcupdate.h:429:0,
			  from include/linux/rcusync.h:5,
			  from kernel/rcu/sync.c:1:
	include/linux/rcutiny.h: In function 'rcu_barrier_sched':
	include/linux/rcutiny.h:55:20: internal compiler error: Segmentation
	fault
	  static inline void rcu_barrier_sched(void)

build failure after ec90a194a "rcu: Create a synchronize_rcu_mult()"
and 114b7fd4b "rcu: Create rcu_sync infrastructure" meet each other.

Reported-and-tested-by: Mark Salter <msalter@...hat.com>
Reported-by: Guenter Roeck <linux@...ck-us.net>
Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 include/linux/rcupdate.h | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index ff47651..c353c2b 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -230,12 +230,11 @@ void __wait_rcu_gp(bool checktiny, int n, call_rcu_func_t *crcu_array,
 		   struct rcu_synchronize *rs_array);
 
 #define _wait_rcu_gp(checktiny, ...) \
-do { \
-	call_rcu_func_t __crcu_array[] = { __VA_ARGS__ }; \
-	const int __n = ARRAY_SIZE(__crcu_array); \
-	struct rcu_synchronize __rs_array[__n]; \
-	\
-	__wait_rcu_gp(checktiny, __n, __crcu_array, __rs_array); \
+do {									\
+	call_rcu_func_t __crcu_array[] = { __VA_ARGS__ }; 		\
+	struct rcu_synchronize __rs_array[ARRAY_SIZE(__crcu_array)];	\
+	__wait_rcu_gp(checktiny, ARRAY_SIZE(__crcu_array),		\
+			__crcu_array, __rs_array); 			\
 } while (0)
 
 #define wait_rcu_gp(...) _wait_rcu_gp(false, __VA_ARGS__)
-- 
2.4.3


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