From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: Re: [PATCH] remove lots of IS_ERR_VALUE abuses Date: Fri, 27 May 2016 14:46:05 -0700 Message-ID: <20160527144605.f2a52ea02cad1297ff188691@linux-foundation.org> References: <1464384685-347275-1-git-send-email-arnd@arndb.de> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: linux-wireless-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, v9fs-developer-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org, linux-acpi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kbuild-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, David Airlie , "Rafael J. Wysocki" , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Adrian Hunter , Andrzej Hajda , iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, Srinivas Kandagatla , netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Bob Peterson , Russell King , Maxime Ripard , Linus Torvalds , Thomas Gleixner , linux-media-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Arnd Bergmann Return-path: In-Reply-To: <1464384685-347275-1-git-send-email-arnd-r2nGTMty4D4@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org List-Id: netdev.vger.kernel.org On Fri, 27 May 2016 23:23:25 +0200 Arnd Bergmann wrote: > Most users of IS_ERR_VALUE() in the kernel are wrong, as they > pass an 'int' into a function that takes an 'unsigned long' > argument. This happens to work because the type is sign-extended > on 64-bit architectures before it gets converted into an > unsigned type. > > However, anything that passes an 'unsigned short' or 'unsigned int' > argument into IS_ERR_VALUE() is guaranteed to be broken, as are > 8-bit integers and types that are wider than 'unsigned long'. > > Andrzej Hajda has already fixed a lot of the worst abusers that > were causing actual bugs, but it would be nice to prevent any > users that are not passing 'unsigned long' arguments. > > This patch changes all users of IS_ERR_VALUE() that I could find > on 32-bit ARM randconfig builds and x86 allmodconfig. For the > moment, this doesn't change the definition of IS_ERR_VALUE() > because there are probably still architecture specific users > elsewhere. So you do plan to add some sort of typechecking into IS_ERR_VALUE()? > Almost all the warnings I got are for files that are better off > using 'if (err)' or 'if (err < 0)'. > The only legitimate user I could find that we get a warning for > is the (32-bit only) freescale fman driver, so I did not remove > the IS_ERR_VALUE() there but changed the type to 'unsigned long'. > For 9pfs, I just worked around one user whose calling conventions > are so obscure that I did not dare change the behavior. > > I was using this definition for testing: > > #define IS_ERR_VALUE(x) ((unsigned long*)NULL == (typeof (x)*)NULL && \ > unlikely((unsigned long long)(x) >= (unsigned long long)(typeof(x))-MAX_ERRNO)) > > which ends up making all 16-bit or wider types work correctly with > the most plausible interpretation of what IS_ERR_VALUE() was supposed > to return according to its users, but also causes a compile-time > warning for any users that do not pass an 'unsigned long' argument. > > I suggested this approach earlier this year, but back then we ended > up deciding to just fix the users that are obviously broken. After > the initial warning that caused me to get involved in the discussion > (fs/gfs2/dir.c) showed up again in the mainline kernel, Linus > asked me to send the whole thing again.