Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933334Ab0BZKMM (ORCPT ); Fri, 26 Feb 2010 05:12:12 -0500 Received: from mail-vw0-f46.google.com ([209.85.212.46]:52897 "EHLO mail-vw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933161Ab0BZKMK (ORCPT ); Fri, 26 Feb 2010 05:12:10 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:mail-followup-to:references :mime-version:content-type:content-disposition:in-reply-to :user-agent; b=BvjQI959CF4eFbcfua9fI4+Zu7fmYKfYyitz1kaWMBxI3HodJ5pzg1t3jtOE+1qlD2 lMblPWyyYqwoq4RexV1wtLF86QXNBI0ngWpn/kAWzm5HsQJ4BUATUvl7Qa6tLVHZTq8V AtDogbGevlPIqwWbEyv780HMj0JQkMYGus1DE= Date: Fri, 26 Feb 2010 13:11:53 +0300 From: Dan Carpenter To: "Steven J. Magnani" Cc: linux-kernel@vger.kernel.org, microblaze-uclinux@itee.uq.edu.au, dan.j.williams@intel.com Subject: Re: Buggy variable-length array code...or compiler? Message-ID: <20100226101153.GB8417@bicker> Mail-Followup-To: Dan Carpenter , "Steven J. Magnani" , linux-kernel@vger.kernel.org, microblaze-uclinux@itee.uq.edu.au, dan.j.williams@intel.com References: <1267139849.3079.68.camel@iscandar.digidescorp.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1267139849.3079.68.camel@iscandar.digidescorp.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2893 Lines: 92 On Thu, Feb 25, 2010 at 05:17:29PM -0600, Steven J. Magnani wrote: > When I run a memcpy dmatest with a Microblaze 2.6.33 noMMU kernel, the > system crashes after about 400 iterations. After much head scratching, I > believe I've narrowed the problem to this fragment of code in > drivers/dma/dmatest.c: > > static int dmatest_func(void *data) > { > struct dmatest_thread *thread = data; > ... > unsigned int total_tests = 0; > int src_cnt; > int dst_cnt; > > ... > if (thread->type == DMA_MEMCPY) > src_cnt = dst_cnt = 1; > ... > > while (!kthread_should_stop() > && !(iterations && total_tests >= iterations)) { > struct dma_device *dev = chan->device; > struct dma_async_tx_descriptor *tx = NULL; > dma_addr_t dma_srcs[src_cnt]; > dma_addr_t dma_dsts[dst_cnt]; > > ... > total_tests++; > > /* CODE ADDED BY ME FOR DEBUG */ > printk("dmatest: Iteration %d, dma_srcs = %p\n", > total_tests, dma_srcs); > > ... > } > > With this code I get output like this: > > dmatest: Iteration 1, dma_srcs = 2c963ee8 > dmatest: Iteration 2, dma_srcs = 2c963ed8 > dmatest: Iteration 3, dma_srcs = 2c963ec8 > dmatest: Iteration 4, dma_srcs = 2c963eb8 > ... > dmatest: Iteration 420, dma_srcs = 2c9624b8 > > ...and then the stack detonates and the kernel crashes with some strange > error or other. > > Are there any language lawyers in the house who'd care to weigh in on > which of these possibilities is the right one? > > 1. There is a coding error in dmatest > 2. There is a bug specific to Microblaze gcc compiler(s) [mine is 4.1.2] > 3. There is a bug generic to specific versions of gcc compilers > 4. There is a bug generic to all gcc compilers > > Obviously, the options get more disturbing the higher you go. I don't > know if VLAs are used elsewhere in the kernel; a 'smatch' search might > be helpful. > Sparse complains about variable length arrays. drivers/dma/dmatest.c:293:37: error: bad constant expression In my allmodconfig with staging: ~/progs/kernel/devel$ grep "bad constant expression" warns.txt | sort -u | wc -l 133 regards, dan carpenter > Regards, > ------------------------------------------------------------------------ > Steven J. Magnani "I claim this network for MARS! > www.digidescorp.com Earthling, return my space modulator!" > > #include > > > > -- > 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/ -- 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/