From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752833Ab2GIKL5 (ORCPT ); Mon, 9 Jul 2012 06:11:57 -0400 Received: from mx1.redhat.com ([209.132.183.28]:40732 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751857Ab2GIKL4 (ORCPT ); Mon, 9 Jul 2012 06:11:56 -0400 Date: Mon, 9 Jul 2012 12:09:20 +0200 From: Oleg Nesterov To: Peter Zijlstra Cc: Ingo Molnar , Srikar Dronamraju , Ananth N Mavinakayanahalli , Anton Arapov , linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/5] uprobes: suppress uprobe_munmap() from mmput() Message-ID: <20120709100920.GA21163@redhat.com> References: <20120708203003.GA18226@redhat.com> <1341822602.3462.15.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1341822602.3462.15.camel@twins> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/09, Peter Zijlstra wrote: > > On Sun, 2012-07-08 at 22:30 +0200, Oleg Nesterov wrote: > > uprobe_munmap() does get_user_pages() and it is also called from > > the final mmput()->exit_mmap() path. This slows down exit/mmput() > > for no reason, and I think it is simply dangerous/wrong to try to > > fault-in a page into the dying mm. If nothing else, this happens > > after the last sync_mm_rss(), afaics handle_mm_fault() can change > > the task->rss_stat and make the subsequent check_mm() unhappy. > > > > Change uprobe_munmap() to check mm->mm_users != 0. > > > > Signed-off-by: Oleg Nesterov > > --- > > kernel/events/uprobes.c | 3 +++ > > 1 files changed, 3 insertions(+), 0 deletions(-) > > > > diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c > > index a93b6df..47c4e24 100644 > > --- a/kernel/events/uprobes.c > > +++ b/kernel/events/uprobes.c > > @@ -1082,6 +1082,9 @@ void uprobe_munmap(struct vm_area_struct *vma, unsigned long start, unsigned lon > > if (!atomic_read(&uprobe_events) || !valid_vma(vma, false)) > > return; > > > > + if (!atomic_read(&vma->vm_mm->mm_users)) /* called by mmput() ? */ > > + return; > > + > > if (!atomic_read(&vma->vm_mm->uprobes_state.count)) > > return; > > > > But won't you leak uprobe refcounts like this? Those aren't tied to the > task (which is dying) but to the vma's mapping the appropriate hunk of > the text. Not doing the munmap will then not put the uprobe->ref.. No, mmap/munmap do not participate in uprobe refcounting. This code does put_uprobe() for each uprobe, yes, but only because the counter was incremented in build_probe_list(). uprobe_munmap() is only needed to decrement mm->uprobes_state.count, but nobody except uprobe_munmap() itself will use it after mmput(). Oleg.