From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759946AbZE2Nwz (ORCPT ); Fri, 29 May 2009 09:52:55 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759485AbZE2Nwp (ORCPT ); Fri, 29 May 2009 09:52:45 -0400 Received: from e23smtp09.au.ibm.com ([202.81.31.142]:38138 "EHLO e23smtp09.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759240AbZE2Nwp (ORCPT ); Fri, 29 May 2009 09:52:45 -0400 Date: Fri, 29 May 2009 19:22:36 +0530 From: "K.Prasad" To: Frederic Weisbecker Cc: David Gibson , Alan Stern , Steven Rostedt , Ingo Molnar , Linux Kernel Mailing List , Andrew Morton , Benjamin Herrenschmidt , maneesh@linux.vnet.ibm.com, Roland McGrath , Masami Hiramatsu Subject: Re: [Patch 06/12] Use the new wrapper routines to access debug registers in process/thread code Message-ID: <20090529135236.GA3465@in.ibm.com> Reply-To: prasad@linux.vnet.ibm.com References: <20090511114422.133566343@prasadkr_t60p.in.ibm.com> <20090511115344.GG25673@in.ibm.com> <20090528064238.GC3091@yookeroo.seuss> <20090529090146.GA5353@in.ibm.com> <20090529104901.GA5997@nowhere> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090529104901.GA5997@nowhere> 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 On Fri, May 29, 2009 at 12:49:03PM +0200, Frederic Weisbecker wrote: > On Fri, May 29, 2009 at 02:31:46PM +0530, K.Prasad wrote: > > On Thu, May 28, 2009 at 04:42:38PM +1000, David Gibson wrote: > > > On Mon, May 11, 2009 at 05:23:44PM +0530, K.Prasad wrote: > > > > From: Alan Stern > > > > > > > > This patch enables the use of abstract debug registers in > > > > process-handling routines. > > > > > > [snip] > > > > > > > > + p->thread.io_bitmap_ptr = NULL; > > > > > > Why is manipulating the io_bitmap_ptr relevant to debug register > > > handling? > > > > I *re-read* the patch but was unable to find how this change had sneaked > > in. It shouldn't be there although it is harmless. > > > When I reviewed this patch, I also ended stucked on it. > But actually I guess I found the sense, this is only for > convenience. > > Look at the current copy_thread() in arch/x86/kernel/process32.c > > If p->thread.io_bitmap_ptr fails to be duplicated, we set > p->thread.io_bitmap_max = 0 and return -ENOMEM > > Now look at the patch. > If we fail to copy the hardware thread virtual registers we > want to exit with io_bitmap_ptr = NULL > If we fail to copy the io_bitmap, we want to free the breakpoint > and exit. > If we fail further, we want to free breakpoints and io_bitmap_ptr > > The out section then tries to: > > -free the breakpoints > -free p->thread.io_bitmap_ptr > > > So it's important to set io_bitmap_ptr to NULL so that > we know whether we have to release it or not. > > aah...yes. It tricked me! It is needed to bring the desired error-return behaviour of copy_thread(). Please ignore this patch (the updation of the comments can be brought in through a separate enhancement patch...see below). > > Hi Frederic, > > I am attaching a new version of this patch 06/12 that: > > > > - removes the line that assigns NULL to "p->thread.io_bitmap_ptr" > > > Dangerous. Unless p->thread.io_bitmap_ptr is already zeroed out > at this stage? > > > > - Updates the comment in __switch_to() function which was stale (was > > relevant when 'last_debugged_task' was used to detect lazy debug > > register switching). > > > > Kindly integrate this version in lieu of the older version sent here: > > http://lkml.org/lkml/2009/5/21/149. > > > Ok. Well it would be nice if you resend the whole series actually :) > Do you have another fix pending? > > Thanks! > In the process of responding to David Gibson's comments I agreed to a few minor/cosmetic changes - say like updation of comments, renaming functions or variables, etc. Given that the patchset is on the verge of integration into -tip tree, I would prefer them to be done through a separate patch (on -tip) for enhancement. Kindly let me know what you think about proceeding this way. Thanks, K.Prasad