From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753637Ab1AZRDh (ORCPT ); Wed, 26 Jan 2011 12:03:37 -0500 Received: from e9.ny.us.ibm.com ([32.97.182.139]:39451 "EHLO e9.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753098Ab1AZRDg (ORCPT ); Wed, 26 Jan 2011 12:03:36 -0500 Date: Wed, 26 Jan 2011 22:26:45 +0530 From: Srikar Dronamraju To: Peter Zijlstra Cc: Ingo Molnar , Steven Rostedt , Linux-mm , Arnaldo Carvalho de Melo , Linus Torvalds , Ananth N Mavinakayanahalli , Christoph Hellwig , Masami Hiramatsu , Oleg Nesterov , Andrew Morton , SystemTap , Jim Keniston , Frederic Weisbecker , Andi Kleen , LKML , "Paul E. McKenney" Subject: Re: [RFC] [PATCH 2.6.37-rc5-tip 5/20] 5: Uprobes: register/unregister probes. Message-ID: <20110126165645.GP19725@linux.vnet.ibm.com> Reply-To: Srikar Dronamraju References: <20101216095714.23751.52601.sendpatchset@localhost6.localdomain6> <20101216095817.23751.76989.sendpatchset@localhost6.localdomain6> <1295957744.28776.722.camel@laptop> <20110126075558.GB19725@linux.vnet.ibm.com> <1296036708.28776.1138.camel@laptop> <20110126153036.GN19725@linux.vnet.ibm.com> <1296056756.28776.1247.camel@laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <1296056756.28776.1247.camel@laptop> User-Agent: Mutt/1.5.20 (2009-06-14) X-Content-Scanned: Fidelis XPS MAILER Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Peter Zijlstra [2011-01-26 16:45:56]: > On Wed, 2011-01-26 at 21:00 +0530, Srikar Dronamraju wrote: > > * Peter Zijlstra [2011-01-26 11:11:48]: > > > > > On Wed, 2011-01-26 at 13:25 +0530, Srikar Dronamraju wrote: > > > > > > > > > > + > > > > > > + list_add(&mm->uprobes_list, &tmp_list); > > > > > > + mm->uprobes_vaddr = vma->vm_start + offset; > > > > > > + } > > > > > > + spin_unlock(&mapping->i_mmap_lock); > > > > > > > > > > Both this and unregister are racy, what is to say: > > > > > - the vma didn't get removed from the mm > > > > > - no new matching vma got added > > > > > > > > > > > > > register_uprobe, unregister_uprobe, uprobe_mmap are all synchronized by > > > > uprobes_mutex. So I dont see one unregister_uprobe getting thro when > > > > another register_uprobe is working with a vma. > > > > > > > > If I am missing something elementary, please explain a bit more. > > > > > > afaict you're not holding the mmap_sem, so userspace can simply unmap > > > the vma. > > > > When we do the actual insert/remove of the breakpoint we hold the > > mmap_sem. During the actual insertion/removal, if the vma for the > > specific inode is not found, we just come out without doing the > > actual insertion/deletion. > > Right, but then install_uprobe() should: > > - lookup the vma relating to the address you stored, We already do this thro get_user_pages in write_opcode(). > - validate that the vma is indeed a map of the right inode We can add a check in write_opcode( we need to pass the inode to write_opcode). > - validate that the offset of the probe corresponds with the stored > address I am not clear on this. We would have derived the address from the offset. So is that we check for (vaddr == vma->vm_start + uprobe->offset) > > Otherwise you can race with unmap/map and end up installing the probe in > a random location. > > Also, I think the whole thing goes funny if someone maps the same text > twice ;-) I am not sure if we can map the same text twice. If something like this is possible then we would have 2 addresses for each function. So how does the linker know which address to jump to out of the 2 or multiple matching addresses. What would be the usecases for same text being mapped multiple times and both being executable? -- Thanks and Regards Srikar