From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andreas Schwab Subject: Re: [BUG -next] "futex: switch to USER_DS for futex test" breaks s390 Date: Fri, 03 Jan 2014 16:41:10 +0100 Message-ID: <87ppo95azt.fsf@igel.home> References: <20140103141943.GA4219@osiris> <20140103153651.GB4219@osiris> Mime-Version: 1.0 Content-Type: text/plain Return-path: Received: from mail-out.m-online.net ([212.18.0.9]:42381 "EHLO mail-out.m-online.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752005AbaACPlP (ORCPT ); Fri, 3 Jan 2014 10:41:15 -0500 In-Reply-To: <20140103153651.GB4219@osiris> (Heiko Carstens's message of "Fri, 3 Jan 2014 16:36:51 +0100") Sender: linux-next-owner@vger.kernel.org List-ID: To: Heiko Carstens Cc: Geert Uytterhoeven , Andrew Morton , Tuxist , Patrick McCarthy , Finn Thain , Rusty Russell , Thomas Gleixner , Darren Hart , Martin Schwidefsky , Linux-Next Heiko Carstens writes: > There is also other code that relies on this: e.g. copy_mount_options() my be > called with KERNEL_DS. With KERNEL_DS you can *only* access kernel memory, which is unpagable. If you want to access user memory, you _must_ use USER_DS. > If DEBUG_PAGEALLOC is turned on, it would crash badly in kernel space > if it crosses page boundaries and touches an invalid page, even though > it should survive... Accessing an invalid page in kernel space is _always_ a bug. Andreas. -- Andreas Schwab, schwab@linux-m68k.org GPG Key fingerprint = 58CA 54C7 6D53 942B 1756 01D3 44D5 214B 8276 4ED5 "And now for something completely different."