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

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Date:	Tue, 25 Aug 2015 12:00:27 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Oleg Nesterov <oleg@...hat.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: Re: [PATCH] rcu: change _wait_rcu_gp() to work around gcc 67055 bug

On Tue, Aug 25, 2015 at 08:45:18PM +0200, Oleg Nesterov wrote:
> 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>

Ouch!!!  Queued for testing, in the absence of problems, will push into
the upcoming merge window.

Thank you all for the testing and the fix!

							Thanx, Paul

> ---
>  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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