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

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Date:	Tue, 25 Aug 2015 21:02:12 +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: Re: [PATCH] rcu: change _wait_rcu_gp() to work around gcc 67055 bug

On 08/25, 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.

and just in case... make make kernel/rcu/rcutorture.o fails the same
way if CONFIG_RCU_TORTURE_TEST && CONFIG_TINY_RCU. So we need a work-
around even before/without rcu_sync.

Oleg.

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