From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Date: Mon, 06 Sep 2010 20:10:55 +0000 Subject: Re: [PATCH] md: do not use ++ in rcu_dereference() argument Message-Id: <201009062210.56824.arnd@arndb.de> List-Id: References: <1283711539-7123-1-git-send-email-segooon@gmail.com> In-Reply-To: <1283711539-7123-1-git-send-email-segooon@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit To: Kulikov Vasiliy , "Paul E. McKenney" Cc: kernel-janitors@vger.kernel.org, Neil Brown , Jens Axboe , linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org On Sunday 05 September 2010 20:32:18 Kulikov Vasiliy wrote: > From: Vasiliy Kulikov > > rcu_dereference() is macro, so it might use its argument twice. > Argument must not has side effects. > > It was found by compiler warning: > drivers/md/raid1.c: In function ‘read_balance’: > drivers/md/raid1.c:445: warning: operation on ‘new_disk’ may be undefined I think the rcu_dereference macro should really not evaluate its argument twice, and I don't see where it does. As a general rule, we try to write macros in Linux such that they behave like functions and don't have surprising side-effects. Which kernel and gcc version do you see the warning with? Arnd From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [PATCH] md: do not use ++ in rcu_dereference() argument Date: Mon, 6 Sep 2010 22:10:55 +0200 Message-ID: <201009062210.56824.arnd@arndb.de> References: <1283711539-7123-1-git-send-email-segooon@gmail.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <1283711539-7123-1-git-send-email-segooon@gmail.com> Sender: linux-raid-owner@vger.kernel.org To: Kulikov Vasiliy , "Paul E. McKenney" Cc: kernel-janitors@vger.kernel.org, Neil Brown , Jens Axboe , linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: linux-raid.ids On Sunday 05 September 2010 20:32:18 Kulikov Vasiliy wrote: > From: Vasiliy Kulikov >=20 > rcu_dereference() is macro, so it might use its argument twice. > Argument must not has side effects. >=20 > It was found by compiler warning: > drivers/md/raid1.c: In function =E2=80=98read_balance=E2=80=99: > drivers/md/raid1.c:445: warning: operation on =E2=80=98new_disk=E2=80= =99 may be undefined I think the rcu_dereference macro should really not evaluate its argume= nt twice, and I don't see where it does. As a general rule, we try to write macros in Linux such that they behav= e like functions and don't have surprising side-effects. Which kernel and gcc version do you see the warning with? Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-raid" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755324Ab0IFULO (ORCPT ); Mon, 6 Sep 2010 16:11:14 -0400 Received: from moutng.kundenserver.de ([212.227.17.10]:61446 "EHLO moutng.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754894Ab0IFULI (ORCPT ); Mon, 6 Sep 2010 16:11:08 -0400 From: Arnd Bergmann To: Kulikov Vasiliy , "Paul E. McKenney" Subject: Re: [PATCH] md: do not use ++ in rcu_dereference() argument Date: Mon, 6 Sep 2010 22:10:55 +0200 User-Agent: KMail/1.13.5 (Linux/2.6.36-rc3; KDE/4.5.1; x86_64; ; ) Cc: kernel-janitors@vger.kernel.org, Neil Brown , Jens Axboe , linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org References: <1283711539-7123-1-git-send-email-segooon@gmail.com> In-Reply-To: <1283711539-7123-1-git-send-email-segooon@gmail.com> MIME-Version: 1.0 Content-Type: Text/Plain; charset="utf-8" Content-Transfer-Encoding: 8bit Message-Id: <201009062210.56824.arnd@arndb.de> X-Provags-ID: V02:K0:aBZBb8txuTNmRWCTNh1rBJC/EikPflajfiwJAm304He 5rZj1xqLBdOzRHfjmFuKsewkWvuI5PbVRiMoXEvSxVlD5zPK45 7A4hj+g+6Yu69EfwJ3eX/BNqmWqoRJr4Crt/4sSaypksesfKFM wygrDJiygiQxwR/8vDt5Hign6dREAlQjwbyX+e3i8ch2aES4A/ tFpehkTcw8zQKZigj/GuQ== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sunday 05 September 2010 20:32:18 Kulikov Vasiliy wrote: > From: Vasiliy Kulikov > > rcu_dereference() is macro, so it might use its argument twice. > Argument must not has side effects. > > It was found by compiler warning: > drivers/md/raid1.c: In function ‘read_balance’: > drivers/md/raid1.c:445: warning: operation on ‘new_disk’ may be undefined I think the rcu_dereference macro should really not evaluate its argument twice, and I don't see where it does. As a general rule, we try to write macros in Linux such that they behave like functions and don't have surprising side-effects. Which kernel and gcc version do you see the warning with? Arnd