From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755684AbbHDJUf (ORCPT ); Tue, 4 Aug 2015 05:20:35 -0400 Received: from casper.infradead.org ([85.118.1.10]:54609 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754495AbbHDJUc (ORCPT ); Tue, 4 Aug 2015 05:20:32 -0400 Date: Tue, 4 Aug 2015 11:20:27 +0200 From: Peter Zijlstra To: Christian Borntraeger Cc: Andrey Konovalov , Ingo Molnar , Paul McKenney , linux-kernel@vger.kernel.org Subject: Re: [PATCH] compiler.h: cast away attributes in WRITE_ONCE magic Message-ID: <20150804092027.GN25159@twins.programming.kicks-ass.net> References: <1438674948-38310-1-git-send-email-borntraeger@de.ibm.com> <1438674948-38310-2-git-send-email-borntraeger@de.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1438674948-38310-2-git-send-email-borntraeger@de.ibm.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Aug 04, 2015 at 09:55:48AM +0200, Christian Borntraeger wrote: > kernel build bot showed a warning triggered by commit > 76695af20c01 ("locking, arch: use WRITE_ONCE()/READ_ONCE() in > smp_store_release()/smp_load_acquire()"). Turns out that sparse > does not like WRITE_ONCE accessing elements from the (sparse) > rcu address space. > > fs/afs/inode.c:448:9: sparse: incorrect type in initializer (different address spaces) > fs/afs/inode.c:448:9: expected struct afs_permits *__val > fs/afs/inode.c:448:9: got void [noderef] * > > Solution is to force cast away the sparse attributes for the initializer > of the union in WRITE_SAME. As this now gets too long, lets split WRITE_ONCE, right? > the macro. > > Signed-off-by: Christian Borntraeger > --- > include/linux/compiler.h | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/include/linux/compiler.h b/include/linux/compiler.h > index e08a6ae..c836eb2 100644 > --- a/include/linux/compiler.h > +++ b/include/linux/compiler.h > @@ -252,7 +252,12 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s > ({ union { typeof(x) __val; char __c[1]; } __u; __read_once_size(&(x), __u.__c, sizeof(x)); __u.__val; }) > > #define WRITE_ONCE(x, val) \ > - ({ union { typeof(x) __val; char __c[1]; } __u = { .__val = (val) }; __write_once_size(&(x), __u.__c, sizeof(x)); __u.__val; }) > +({ \ > + union { typeof(x) __val; char __c[1]; } __u = \ > + { .__val = (__force typeof(x)) (val) }; \ > + __write_once_size(&(x), __u.__c, sizeof(x)); \ > + __u.__val; \ > +}) Thanks! READ_ONCE() doesn't have a similar problem because it only has the one input type, which automagically becomes the output type, right?