From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752637AbYK0G1j (ORCPT ); Thu, 27 Nov 2008 01:27:39 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751380AbYK0G1b (ORCPT ); Thu, 27 Nov 2008 01:27:31 -0500 Received: from gw-ca.panasas.com ([66.104.249.162]:17236 "EHLO laguna.int.panasas.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751290AbYK0G1a (ORCPT ); Thu, 27 Nov 2008 01:27:30 -0500 Message-ID: <492E3DE7.9040107@panasas.com> Date: Thu, 27 Nov 2008 08:27:51 +0200 From: Benny Halevy User-Agent: Thunderbird 3.0a1 (X11/2008050714) MIME-Version: 1.0 To: Andrew Morton CC: linux-kernel@vger.kernel.org Subject: Re: WARN_ON out of range error in ERR_PTR? References: <492D6FB8.80401@panasas.com> <20081126161503.6211f140.akpm@linux-foundation.org> In-Reply-To: <20081126161503.6211f140.akpm@linux-foundation.org> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-OriginalArrivalTime: 27 Nov 2008 06:26:02.0977 (UTC) FILETIME=[0567CD10:01C95059] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Nov. 27, 2008, 2:15 +0200, Andrew Morton wrote: > On Wed, 26 Nov 2008 17:48:08 +0200 > Benny Halevy wrote: > >> Andrew, >> >> After hitting a bug where an nfs error -10021 wasn't handled >> correctly since IS_ERR returned false on its ERR_PTR value > > That sounds like an error in NFS. Did it get fixed? Right, it is an error I made when developing new code for nfs41 and I caught and fixed it in my branch before releasing the code. I just thought that this WARN_ON could be beneficial for everybody... Benny > >> I realized that adding a BUG_ON to make sure the mapped error >> is in the valid range would have caught this. >> >> Since ERR_PTR is not called on the critical path >> (unlike IS_ERR) but rather on the error handling path I believe >> we can tolerate the extra cost. >> >> The reason this is just a WARN_ON and not BUG_ON is to make >> fixing it easier, although I do consider calling ERR_PTR on an >> out of range error a pretty dangerous bug as the error might go >> unnoticed. >> >> How about committing the following patch to -mm? >> >> Signed-off-by: Benny Halevy >> --- >> include/linux/err.h | 3 ++- >> 1 files changed, 2 insertions(+), 1 deletions(-) >> >> diff --git a/include/linux/err.h b/include/linux/err.h >> index ec87f31..81df84f 100644 >> --- a/include/linux/err.h >> +++ b/include/linux/err.h >> @@ -2,7 +2,7 @@ >> #define _LINUX_ERR_H >> >> #include >> - >> +#include >> #include >> >> /* >> @@ -21,6 +21,7 @@ >> >> static inline void *ERR_PTR(long error) >> { >> + WARN_ON(error && !IS_ERR_VALUE(error)); >> return (void *) error; >> } > > We have over 2000 ERR_PTR callsites, and WARN_ON() is a big fat porky > thing, so this change would add quite a lot of kernel text&data. > > If this problem does occur again, I expect that the kernel will > reliably dereference a small negative address and we'll get an oops, > which will give us the same information as that WARN_ON would have > done, no? > > >