Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753872AbZGFOn5 (ORCPT ); Mon, 6 Jul 2009 10:43:57 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752814AbZGFOnu (ORCPT ); Mon, 6 Jul 2009 10:43:50 -0400 Received: from mail-fx0-f218.google.com ([209.85.220.218]:41760 "EHLO mail-fx0-f218.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753349AbZGFOnt (ORCPT ); Mon, 6 Jul 2009 10:43:49 -0400 Message-ID: <4A520DA6.2040107@petalogix.com> Date: Mon, 06 Jul 2009 16:43:50 +0200 From: Michal Simek Reply-To: michal.simek@petalogix.com User-Agent: Thunderbird 2.0.0.18 (X11/20081120) MIME-Version: 1.0 To: Arnd Bergmann CC: Paul Mundt , Linux Kernel list , LTP , John Williams , Ingo Molnar , Andrew Morton , Grant Likely , subrata@linux.vnet.ibm.com Subject: Re: mmap syscall problem References: <4A4DFB77.1080700@petalogix.com> <20090706121455.GA16908@linux-sh.org> <4A51F3F3.6040501@petalogix.com> <200907061616.12220.arnd@arndb.de> In-Reply-To: <200907061616.12220.arnd@arndb.de> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2063 Lines: 70 Arnd Bergmann wrote: > On Monday 06 July 2009, Michal Simek wrote: > >>> Not necessarily, even on platforms that manage aliases in hardware >>> mappings that violate the aliasing constraints can still result in >>> undefined behaviour, this really depends more on your cache controller >>> and MMU than anything else. I notice that microblaze sets SHMLBA to >>> PAGE_SIZE, you may want to see if this test still breaks after bumping it >>> up to something like PAGE_SIZE * 4. >>> >>> >> Yes, test still break - behavior is the same. I don't have accurate >> information about MMU unit >> but I will ask a question about. We are able to turn off cache >> controller directly in HW. >> > > There may still be a problem with data being queued in some write > buffers that don't get flushed before reading back from another > address. > > What happens in a simple user space program that mmaps the same > page to two addresses? Something like > > #include > #include > int main(void) > { > int fd = open("existing-4k-file", O_RDWR); > char *p1 = mmap(0, 4096, PROT_READ | PROT_WRITE, > MAP_SHARED, fd, 0); > char *p2 = mmap(p1 + 4096, 4096, PROT_READ | PROT_WRITE, > MAP_SHARED | MAP_FIXED, fd, 0); > > *p1 = 0xaa; *p2 = 0x55; > I closed fd too. close(fd); > return *p1; /* returns 0xaa if broken, 0x55 if correct */ > } > # ls -la existing-4k-file -rw-rw-r-- 1 monstr monstr 4096 Jul 6 2009 existing-4k-file # ./test-arnd # echo $? 85 # dd if=existing-4k-file of=/dev/console count=1 2>/dev/null U# in file is first char U (0x55) which is IMO correct. Michal > Arnd <>< > -- Michal Simek, Ing. (M.Eng) PetaLogix - Linux Solutions for a Reconfigurable World w: www.petalogix.com p: +61-7-30090663,+42-0-721842854 f: +61-7-30090663 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/