From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755668Ab2HZACJ (ORCPT ); Sat, 25 Aug 2012 20:02:09 -0400 Received: from e33.co.us.ibm.com ([32.97.110.151]:34455 "EHLO e33.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754469Ab2HZACC (ORCPT ); Sat, 25 Aug 2012 20:02:02 -0400 Date: Sat, 25 Aug 2012 17:01:49 -0700 From: "Paul E. McKenney" To: Fengguang Wu Cc: Josh Triplett , Lai Jiangshan , linux-kernel@vger.kernel.org Subject: Re: INFO: suspicious RCU usage in rcu_torture_writer() Message-ID: <20120826000149.GG3436@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20120825033623.GA19330@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120825033623.GA19330@localhost> User-Agent: Mutt/1.5.21 (2010-09-15) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12082600-2398-0000-0000-000009C3F0C8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Aug 25, 2012 at 11:36:23AM +0800, Fengguang Wu wrote: > Greetings, > > I got this warning on 3.6.0-rc2. Full dmesg/config attached. > > [ 3.051375] Initializing RT-Tester: OK > [ 3.052491] rcu-torture:--- Start of test: nreaders=2 nfakewriters=4 stat_interval=0 verbose=0 test_no_idle_hz=0 shuffle_interval=3 stut > ter=5 irqreader=1 fqs_duration=0 fqs_holdoff=0 fqs_stutter=3 test_boost=1/1 test_boost_interval=7 test_boost_duration=4 shutdown_secs=0 onoff_interval=0 onoff_holdoff=0 > [ 3.059084] > [ 3.059451] =============================== > [ 3.060454] [ INFO: suspicious RCU usage. ] > [ 3.061482] 3.6.0-rc2-00010-g4c58c42 #59 Not tainted > [ 3.062686] ------------------------------- > [ 3.063744] /c/kernel-tests/src/stable/kernel/rcutorture.c:990 suspicious rcu_dereference_check() usage! > > 982 do { > 983 schedule_timeout_uninterruptible(1); > 984 rp = rcu_torture_alloc(); > 985 if (rp == NULL) > 986 continue; > 987 rp->rtort_pipe_count = 0; > 988 udelay(rcu_random(&rand) & 0x3ff); > 989 old_rp = rcu_dereference_check(rcu_torture_current, > >990 current == writer_task); > 991 rp->rtort_mbtest = 1; > 992 rcu_assign_pointer(rcu_torture_current, rp); > 993 smp_wmb(); /* Mods to old_rp must follow rcu_assign_pointer() */ > 994 if (old_rp) { Does the following clear this up? Thanx, Paul ------------------------------------------------------------------------ rcu: Prevent initialization race in rcutorture kthreads When you do something like "t = kthread_run(...)", it is possible that the kthread will start running before the assignment to "t" happens. If the child kthread expects to find a pointer to its task_struct in "t", it will then be fatally disappointed. This commit therefore switches such cases to kthread_create() followed by wake_up_process(), guaranteeing that the assignment happens before the child kthread starts running. Reported-by: Fengguang Wu Signed-off-by: Paul E. McKenney diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c index 7a97b5b..8ff4fad 100644 --- a/kernel/rcutorture.c +++ b/kernel/rcutorture.c @@ -2028,14 +2028,15 @@ rcu_torture_init(void) /* Start up the kthreads. */ VERBOSE_PRINTK_STRING("Creating rcu_torture_writer task"); - writer_task = kthread_run(rcu_torture_writer, NULL, - "rcu_torture_writer"); + writer_task = kthread_create(rcu_torture_writer, NULL, + "rcu_torture_writer"); if (IS_ERR(writer_task)) { firsterr = PTR_ERR(writer_task); VERBOSE_PRINTK_ERRSTRING("Failed to create writer"); writer_task = NULL; goto unwind; } + wake_up_process(writer_task); fakewriter_tasks = kzalloc(nfakewriters * sizeof(fakewriter_tasks[0]), GFP_KERNEL); if (fakewriter_tasks == NULL) { @@ -2150,14 +2151,15 @@ rcu_torture_init(void) } if (shutdown_secs > 0) { shutdown_time = jiffies + shutdown_secs * HZ; - shutdown_task = kthread_run(rcu_torture_shutdown, NULL, - "rcu_torture_shutdown"); + shutdown_task = kthread_create(rcu_torture_shutdown, NULL, + "rcu_torture_shutdown"); if (IS_ERR(shutdown_task)) { firsterr = PTR_ERR(shutdown_task); VERBOSE_PRINTK_ERRSTRING("Failed to create shutdown"); shutdown_task = NULL; goto unwind; } + wake_up_process(shutdown_task); } i = rcu_torture_onoff_init(); if (i != 0) {