From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755892Ab2E2XFF (ORCPT ); Tue, 29 May 2012 19:05:05 -0400 Received: from merlin.infradead.org ([205.233.59.134]:43442 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752430Ab2E2XFD convert rfc822-to-8bit (ORCPT ); Tue, 29 May 2012 19:05:03 -0400 Message-ID: <1338332687.26856.189.camel@twins> Subject: Re: [PATCH 7/7] uprobes: kill uprobes_srcu/uprobe_srcu_id From: Peter Zijlstra To: Oleg Nesterov Cc: Ingo Molnar , Srikar Dronamraju , Ananth N Mavinakayanahalli , Anton Arapov , Linus Torvalds , Masami Hiramatsu , linux-kernel@vger.kernel.org, "Paul E. McKenney" Date: Wed, 30 May 2012 01:04:47 +0200 In-Reply-To: <20120529193008.GG8057@redhat.com> References: <20120529192721.GA8048@redhat.com> <20120529193008.GG8057@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 Tue, 2012-05-29 at 21:30 +0200, Oleg Nesterov wrote: > Kill the no longer needed uprobes_srcu/uprobe_srcu_id code. > > It doesn't really work anyway. synchronize_srcu() can only synchronize > with the code "inside" the srcu_read_lock/srcu_read_unlock section, > while uprobe_pre_sstep_notifier() does srcu_read_lock() _after_ we > already hit the breakpoint. > > I guess this probably works "in practice". synchronize_srcu() is slow > and it implies synchronize_sched(), and the probed task enters the non- > preemptible section at the start of exception handler. Still this is not > right at least in theory, and task->uprobe_srcu_id blows task_struct. This kills the only user of srcu_read_{,un}lock_raw(), so I guess we could also make: 9ceae0e2 101db7b4 0c53dd8b go away..