From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752954Ab3KKImA (ORCPT ); Mon, 11 Nov 2013 03:42:00 -0500 Received: from mail-ea0-f172.google.com ([209.85.215.172]:36640 "EHLO mail-ea0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751477Ab3KKIlw (ORCPT ); Mon, 11 Nov 2013 03:41:52 -0500 Date: Mon, 11 Nov 2013 09:41:49 +0100 From: Ingo Molnar To: Oleg Nesterov Cc: Ingo Molnar , Srikar Dronamraju , linux-kernel@vger.kernel.org Subject: Re: [PATCH] uprobes: Cleanup !CONFIG_UPROBES decls, unexport xol_area Message-ID: <20131111084149.GC12405@gmail.com> References: <20131109190344.GA32281@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20131109190344.GA32281@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Oleg Nesterov wrote: > +++ b/kernel/events/uprobes.c > @@ -86,6 +86,25 @@ struct return_instance { > }; > > /* > + * On a breakpoint hit, thread contests for a slot. It frees the > + * slot after singlestep. Currently a fixed number of slots are > + * allocated. > + */ > +struct xol_area { So, my main complaint about the uprobes code isn't functional but documentational, similar to what I outlined a few days ago: what this comment does not explain is exactly what a 'XOL area' is. You guys are changing code that reads like gobbledygook to people reading it for the first time. It's understandable that you want to use abbreviations and I don't object against that, but please explain key concepts and data structures when they first come up - a very good place to do that is in places where key structures are declared. I didn't find any high level description of the XOL code, one which makes clear that how we manage these out of line execution areas: comet:~/tip> git grep -i 'out of line' $(find . -name '*uprobe*.[ch]') arch/powerpc/kernel/uprobes.c: * arch_uprobe_pre_xol - prepare to execute out of line. arch/x86/kernel/uprobes.c: * arch_uprobe_pre_xol - prepare to execute out of line. arch/x86/kernel/uprobes.c: * address pushed by a call instruction executed out of line. kernel/events/uprobes.c: * This area will be used for storing instructions for execution out of line. kernel/events/uprobes.c:/* Prepare to single-step probed instruction out of line. */ The one that comes closest is: * This area will be used for storing instructions for execution out of line. ... but that is a single sentence and deep inside the XOL code already. Really, please make a better job of introducing other kernel hackers to the code you are writing ... Maybe even split the XOL code out into kernel/events/uprobes_xol.c or so? That will give a natural place to explain yourselves at the beginning of the file. Thanks, Ingo