From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756047Ab1KXO02 (ORCPT ); Thu, 24 Nov 2011 09:26:28 -0500 Received: from e4.ny.us.ibm.com ([32.97.182.144]:47186 "EHLO e4.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752719Ab1KXO01 (ORCPT ); Thu, 24 Nov 2011 09:26:27 -0500 Date: Thu, 24 Nov 2011 19:55:07 +0530 From: Srikar Dronamraju To: Peter Zijlstra Cc: Linus Torvalds , Oleg Nesterov , Andrew Morton , LKML , Linux-mm , Ingo Molnar , Andi Kleen , Christoph Hellwig , Steven Rostedt , Roland McGrath , Thomas Gleixner , Masami Hiramatsu , Arnaldo Carvalho de Melo , Anton Arapov , Ananth N Mavinakayanahalli , Jim Keniston , Stephen Wilson , tulasidhard@gmail.com Subject: Re: [PATCH v7 3.2-rc2 4/30] uprobes: Define hooks for mmap/munmap. Message-ID: <20111124142507.GI28065@linux.vnet.ibm.com> Reply-To: Srikar Dronamraju References: <20111118110631.10512.73274.sendpatchset@srdronam.in.ibm.com> <20111118110723.10512.66282.sendpatchset@srdronam.in.ibm.com> <1322071812.14799.87.camel@twins> <20111124134742.GH28065@linux.vnet.ibm.com> <1322144017.2921.57.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <1322144017.2921.57.camel@twins> User-Agent: Mutt/1.5.20 (2009-06-14) x-cbid: 11112414-3534-0000-0000-000002C768DF Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Peter Zijlstra [2011-11-24 15:13:37]: > On Thu, 2011-11-24 at 19:17 +0530, Srikar Dronamraju wrote: > > * Peter Zijlstra [2011-11-23 19:10:12]: > > > > > On Fri, 2011-11-18 at 16:37 +0530, Srikar Dronamraju wrote: > > > > + ret = install_breakpoint(vma->vm_mm, uprobe); > > > > + if (ret == -EEXIST) { > > > > + atomic_inc(&vma->vm_mm->mm_uprobes_count); > > > > + ret = 0; > > > > + } > > > > > > Aren't you double counting that probe position here? The one that raced > > > you to inserting it will also have incremented that counter, no? > > > > > > > No we arent. > > Because register_uprobe can never race with mmap_uprobe and register > > before mmap_uprobe registers .(Once we start mmap_region, > > register_uprobe waits for the read_lock of mmap_sem.) > > Still doesn't make any sense. Since you don't increment on success, one > has to assume install_breakpoint() will cause an increment. Therefore, > when we encounter -EEXIST we'll already have accounted for this > mm,inode,offset combination. > In the success case, install_breakpoint itself does the increment. We cant allow install_breakpoint to increment in EEXIST case always because doing that in register_uprobe context would increment which is wrong. > But I'll have another look at it, maybe I'm missing something > obvious :-) > > > And we badly need this for mmap_uprobe case. Because when we do mremap, > > or vma_adjust(), we do a munmap_uprobe() followed by mmap_uprobe() which > > would have decremented the count but not removed it. So when we do a > > mmap_uprobe, we need to increment the count. > > Well I see why the count needs to be correct, that's not the issue. Okay .. -- Thanks and Regards Srikar