From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with ESMTP id E9E196B0092 for ; Wed, 26 Jan 2011 10:45:23 -0500 (EST) Subject: Re: [RFC] [PATCH 2.6.37-rc5-tip 5/20] 5: Uprobes: register/unregister probes. From: Peter Zijlstra In-Reply-To: <20110126153036.GN19725@linux.vnet.ibm.com> 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> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Date: Wed, 26 Jan 2011 16:45:56 +0100 Message-ID: <1296056756.28776.1247.camel@laptop> Mime-Version: 1.0 Sender: owner-linux-mm@kvack.org To: Srikar Dronamraju 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" List-ID: On Wed, 2011-01-26 at 21:00 +0530, Srikar Dronamraju wrote: > * Peter Zijlstra [2011-01-26 11:11:48]: >=20 > > On Wed, 2011-01-26 at 13:25 +0530, Srikar Dronamraju wrote: > > >=20 > > > > > + > > > > > + list_add(&mm->uprobes_list, &tmp_list); > > > > > + mm->uprobes_vaddr =3D vma->vm_start + offset; > > > > > + } > > > > > + spin_unlock(&mapping->i_mmap_lock); > > > >=20 > > > > 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 > > > >=20 > > >=20 > > > 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. > > >=20 > > > If I am missing something elementary, please explain a bit more. > >=20 > > afaict you're not holding the mmap_sem, so userspace can simply unmap > > the vma. >=20 > 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, - validate that the vma is indeed a map of the right inode - validate that the offset of the probe corresponds with the stored address 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 ;-) -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: email@kvack.org