From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754533Ab2HBQzO (ORCPT ); Thu, 2 Aug 2012 12:55:14 -0400 Received: from e9.ny.us.ibm.com ([32.97.182.139]:60466 "EHLO e9.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754478Ab2HBQzM (ORCPT ); Thu, 2 Aug 2012 12:55:12 -0400 Date: Thu, 2 Aug 2012 22:24:52 +0530 From: Srikar Dronamraju To: Oleg Nesterov Cc: Ingo Molnar , Anton Arapov , "Frank Ch. Eigler" , Peter Zijlstra , William Cohen , linux-kernel@vger.kernel.org Subject: Re: [PATCH] uprobes: Ignore unsupported instructions in uprobe_mmap Message-ID: <20120802165452.GB4268@linux.vnet.ibm.com> Reply-To: Srikar Dronamraju References: <20120728163157.GA22719@redhat.com> <20120731064730.GB5087@linux.vnet.ibm.com> <20120731124805.GA485@redhat.com> <20120802100515.GC5782@linux.vnet.ibm.com> <20120802141757.GA5064@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20120802141757.GA5064@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12080216-7182-0000-0000-00000226E159 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Oleg Nesterov [2012-08-02 16:17:57]: > Forgot to mention... > > On 08/02, Srikar Dronamraju wrote: > > > > While at it, add a missing put_uprobe() in the path where uprobe_mmap() > > races with uprobe_unregister(). > > ... > > @@ -1051,8 +1051,10 @@ int uprobe_mmap(struct vm_area_struct *vma) > > if (ret == -EEXIST) { > > ret = 0; > > > > - if (!is_swbp_at_addr(vma->vm_mm, vaddr)) > > + if (!is_swbp_at_addr(vma->vm_mm, vaddr)) { > > + put_uprobe(uprobe); > > continue; > > + } > > Yes, this part looks correct. > > In fact, I think this is not really correct anyway (wrt counter) > but we are going to kill it. > > Are you expecting the counter to be decreased/increased here? This is case where the uprobe_mmap() and uprobe_unregister() raced, and by the time install_breakpoint() was called by uprobe_mmap(), there were no consumers. i.e there are no uprobe->consumers and the underlying instruction is still not a breakpoint instruction. Since we are refusing to add a breakpoint and that there is no breakpoint, there is no need to increment/decrement the counter here. Do let me know if I have missed something. -- Thanks and Regards Srikar