From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932156Ab2DQKIu (ORCPT ); Tue, 17 Apr 2012 06:08:50 -0400 Received: from casper.infradead.org ([85.118.1.10]:45569 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932096Ab2DQKIt convert rfc822-to-8bit (ORCPT ); Tue, 17 Apr 2012 06:08:49 -0400 Message-ID: <1334657287.28150.77.camel@twins> Subject: Re: [PATCH 2/6] uprobes: introduce is_swbp_at_addr_fast() From: Peter Zijlstra To: Oleg Nesterov Cc: Ingo Molnar , Srikar Dronamraju , Andrew Morton , Linus Torvalds , Ananth N Mavinakayanahalli , Jim Keniston , LKML , Linux-mm , Andi Kleen , Christoph Hellwig , Steven Rostedt , Arnaldo Carvalho de Melo , Masami Hiramatsu , Thomas Gleixner , Anton Arapov Date: Tue, 17 Apr 2012 12:08:07 +0200 In-Reply-To: <20120416153408.GA8852@redhat.com> References: <20120405222024.GA19154@redhat.com> <20120405222106.GB19166@redhat.com> <1334570935.28150.25.camel@twins> <20120416144457.GA7018@redhat.com> <1334588109.28150.59.camel@twins> <20120416153408.GA8852@redhat.com> Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT X-Mailer: Evolution 3.2.2- Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2012-04-16 at 17:34 +0200, Oleg Nesterov wrote: > On 04/16, Peter Zijlstra wrote: > > > > Can't we 'optimize' read_opcode() by doing the pagefault_disable() + > > __copy_from_user_inatomic() optimistically before going down the whole > > gup()+lock+kmap path? > > Unlikely, the task is not current. Easy enough to test that though.. and that should make the regular path fast enough, no? --- kernel/events/uprobes.c | 9 +++++++++ 1 files changed, 9 insertions(+), 0 deletions(-) diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c index 985be4d..7f5d8c5 100644 --- a/kernel/events/uprobes.c +++ b/kernel/events/uprobes.c @@ -312,6 +312,15 @@ static int read_opcode(struct mm_struct *mm, unsigned long vaddr, uprobe_opcode_ void *vaddr_new; int ret; + if (mm == current->mm) { + pagefault_disable(); + ret = __copy_from_user_inatomic(opcode, (void __user *)vaddr, + sizeof(*opcode)); + pagefault_enable(); + if (!ret) + return 0; + } + ret = get_user_pages(NULL, mm, vaddr, 1, 0, 0, &page, NULL); if (ret <= 0) return ret;