Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161533Ab2JXWcS (ORCPT ); Wed, 24 Oct 2012 18:32:18 -0400 Received: from mail-vb0-f46.google.com ([209.85.212.46]:52068 "EHLO mail-vb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1161362Ab2JXWcP (ORCPT ); Wed, 24 Oct 2012 18:32:15 -0400 MIME-Version: 1.0 In-Reply-To: <20121024182111.GA2340@swordfish> References: <20121017034918.GA13295@redhat.com> <20121024164235.GA2467@swordfish> <20121024180608.GA22840@redhat.com> <20121024182111.GA2340@swordfish> Date: Thu, 25 Oct 2012 00:32:14 +0200 Message-ID: Subject: Re: lots of suspicious RCU traces From: Frederic Weisbecker To: Sergey Senozhatsky Cc: Oleg Nesterov , Dave Jones , "Paul E. McKenney" , Serge Hallyn , linux-kernel@vger.kernel.org Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1294 Lines: 32 First of all, thanks a lot for your report. 2012/10/24 Sergey Senozhatsky : > On (10/24/12 20:06), Oleg Nesterov wrote: >> On 10/24, Sergey Senozhatsky wrote: >> > >> > small question, >> > >> > ptrace_notify() and forward calls are able to both indirectly and directly call schedule(), >> > /* direct call from ptrace_stop()*/, >> > should, in this case, rcu_user_enter() be called before tracehook_report_syscall_exit(regs, step) >> > and ptrace chain? >> >> Well, I don't really understand this magic... but why? >> > > My understanding is (I may be wrong) that we can schedule() from ptrace chain to > some arbitrary task, which will continue its execution from the point where RCU assumes > CPU as not idle, while CPU in fact still in idle state -- no one said rcu_idle_exit() > (or similar) prior to schedule() call. Yeah but when we are in syscall_trace_leave(), the CPU shouldn't be in RCU idle mode. That's where the bug is. How do you manage to trigger this bug? > > if so, does the same apply to in_user? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/