From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754377Ab2AJLAL (ORCPT ); Tue, 10 Jan 2012 06:00:11 -0500 Received: from cam-admin0.cambridge.arm.com ([217.140.96.50]:34760 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752853Ab2AJLAJ (ORCPT ); Tue, 10 Jan 2012 06:00:09 -0500 Date: Tue, 10 Jan 2012 10:59:55 +0000 From: Catalin Marinas To: "tiejun.chen" Cc: "linux-kernel@vger.kernel.org" Subject: Re: [PATCH 1/1] kmemleak/module: only scan the existed data section Message-ID: <20120110105955.GK29581@arm.com> References: <1325059891-20540-1-git-send-email-tiejun.chen@windriver.com> <4F0BA99E.1090006@windriver.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4F0BA99E.1090006@windriver.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 10, 2012 at 02:59:42AM +0000, tiejun.chen wrote: > Catalin Marinas wrote: > > I would rather move this check to kmemleak.c. But why would it be > > needed? Performance? A zero-size area shouldn't be scanned anyway. > > When we call layout_sections() to calculate sh_entsize, often a zero-sized > .data/.bss section would be ordered as a middle of all valid sections. For example, > ------ > Symbol Addr size > > .init. 0xf96d3000 > ...... > .data(or .bss) 0xf96d3180 0 > ...... 0xf96d4000 > > If so kmemleak_scan_area(0xf96d3180,0,GFP_KERNEL) is fine as we expect since > 0xf96d3180 is always within a valid address scopes summarized all section, > 0xf96d3000 ~ 0xf96d4000. But sometimes if that is arranged as a last section: > ----- > Symbol Addr size > > .init. 0xf96d3000 > ...... > .data(or .bss) 0xf96d3180 0 > > > An then the following call trace is triggered > ...... > kmemleak: Adding scan area to unknown object at 0xf96d3180 > Call Trace: > [e9095de0] [c0008588] show_stack+0x68/0x1d8 (unreliable) > [e9095e30] [c0690094] dump_stack+0x2c/0x44 > [e9095e40] [c015a190] kmemleak_scan_area+0x128/0x184 > [e9095e70] [c00a145c] load_module+0xa98/0x1c04 > [e9095f10] [c00a2650] sys_init_module+0x88/0x24c > [e9095f40] [c0012f7c] ret_from_syscall+0x0/0x4 > --- Exception: c01 at 0xff63564 > LR = 0x10003414 Ah, good find. As I said, I would check the size in the kmemleak_scan_area() function and ignore if 0 (same as the ptr check). Thanks. -- Catalin