From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753464Ab3IWUPN (ORCPT ); Mon, 23 Sep 2013 16:15:13 -0400 Received: from e36.co.us.ibm.com ([32.97.110.154]:53714 "EHLO e36.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752648Ab3IWUPK (ORCPT ); Mon, 23 Sep 2013 16:15:10 -0400 Date: Mon, 23 Sep 2013 13:14:49 -0700 From: "Paul E. McKenney" To: Kirill Tkhai Cc: "linux-kernel@vger.kernel.org" , Dipankar Sarma Subject: Re: [PATCH] rcu: Fix CONFIG_RCU_NOCB_CPU_ALL panic on machines with sparse CPU mask Message-ID: <20130923201449.GT9093@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <191071379163800@web12j.yandex.ru> <20130914184801.GL3966@linux.vnet.ibm.com> <13641379251757@web21g.yandex.ru> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <13641379251757@web21g.yandex.ru> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13092320-3532-0000-0000-000001A60F2E Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Sep 15, 2013 at 05:29:17PM +0400, Kirill Tkhai wrote: > 14.09.2013, 22:48, "Paul E. McKenney" : > > On Sat, Sep 14, 2013 at 05:03:20PM +0400, Kirill Tkhai wrote: > > > >>  When a system has a sparse cpumask and CONFIG_RCU_NOCB_CPU_ALL is enabled, > >>  rcu_spawn_nocb_kthreads() creates nocb threads for nonexistent CPUS. > >> > >>  The problem is in rcu_bootup_announce_oddness(). cpumask_setall() sets all > >>  bits from 0 to nr_cpu_ids existent and nonexistent CPUs both. > >> > >>  The sample. My cpuinfo(sparc64): > >> > >>  CPU0: online > >>  CPU2: online > >> > >>  I get these oopses every boot: > >> > >>  Unable to handle kernel NULL pointer dereference > >>  CPU: 0 PID: 23 Comm: rcuos/1 Not tainted 3.11.0+ #103 > >>  task: fffff800be9792c0 ti: fffff800be98c000 task.ti: fffff800be98c000 > >>  TSTATE: 0000004480e01604 TPC: 000000000047cffc TNPC: 000000000047d000 Y: 00000000    Not tainted > >>  TPC: > >>  g0: 0000000000000000 g1: 0000000000000000 g2: fffff800be98fd58 g3: 0000000000acb718 > >>  g4: fffff800be9792c0 g5: fffff800be536000 g6: fffff800be98c000 g7: 0000000000000000 > >>  o0: 0000000000000000 o1: 0000000000a33d34 o2: 0000000000000001 o3: 0000000000000000 > >>  o4: 0000000000000000 o5: 0000000000000000 sp: fffff800be98f3d1 ret_pc: 000000000047cfd8 > >>  RPC: > >>  l0: 0000000000a33ce8 l1: 0000000000000001 l2: 0000000000a7d800 l3: fffff800bf004dc0 > >>  l4: fffff800be880310 l5: 0000000000a33ce8 l6: 0000000000ad0000 l7: 0000000000a33800 > >>  i0: 0000000000acb710 i1: fffff800be98fd40 i2: 0000000000000001 i3: fffff800be98fd40 > >>  i4: 0000000000000000 i5: 0000000000000000 i6: fffff800be98f491 i7: 00000000004d3f50 > >>  I7: > >>  Call Trace: > >>   [00000000004d3f50] rcu_nocb_kthread+0x5c/0x224 > >>   [000000000047c604] kthread+0x88/0x9c > >>   [0000000000406084] ret_from_fork+0x1c/0x2c > >>   [0000000000000000]           (null) > >> > >>  So, not possible CPUs have to be cleared. > > > > Good catch! > > > > I am hoping that your setup always has CPU 0 defined.  If not, there are > > many other problems in addition to CONFIG_RCU_NOCB_CPU_ZERO=y! > > I've never seen machines like you said, but it seem they are possible. boot_cpu_init() accounts > the fact kernel may boot from not zero CPU: > > static void __init boot_cpu_init(void) > { > int cpu = smp_processor_id(); > /* Mark the boot cpu "present", "online" etc for SMP and UP case */ > set_cpu_online(cpu, true); > set_cpu_active(cpu, true); > set_cpu_present(cpu, true); > set_cpu_possible(cpu, true); > } > > >>  Signed-off-by: Kirill Tkhai > >>  CC: Dipankar Sarma > >>  CC: Paul E. McKenney > >>  --- > >>   kernel/rcutree_plugin.h |    1 + > >>   1 files changed, 1 insertions(+), 0 deletions(-) > >>  diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h > >>  index 130c97b..1f17e99 100644 > >>  --- a/kernel/rcutree_plugin.h > >>  +++ b/kernel/rcutree_plugin.h > >>  @@ -97,6 +97,7 @@ static void __init rcu_bootup_announce_oddness(void) > >>   #ifdef CONFIG_RCU_NOCB_CPU_ALL > >>           pr_info("\tOffload RCU callbacks from all CPUs\n"); > >>           cpumask_setall(rcu_nocb_mask); > >>  + cpumask_and(rcu_nocb_mask, cpu_possible_mask, rcu_nocb_mask); > > > > Would it make sense to combine the cpumask_setall() and the cpumask_and() > > into a single cpumask_copy()? > > > >>   #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */ > >>   #endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */ > >>           if (have_rcu_nocb_mask) { > > > > Do we need a cpumask_and() within this "if" statement to handle the > > case where the kernel's rcu_nocbs= boot parameter specified a CPU > > that is not present?  (If so, probably also giving a warning about the > > non-present CPUs specified.) > > > > I believe that the answer to both questions is "yes", and I would > > welcome an updated patch that covered these cases. > > Yes and yes. New patch is below. > > > All that said...  Why does the system have a sparse cpu_possible_mask? > > This does cause overallocation of memory in a number of areas, including > > RCU's combining tree of rcu_node structures, to say nothing of the > > cpumasks themselves. > > In case of sparc64 the cpu number is configured by boot/openprom. Kernel > doesn't change it. I have not touched inside of them, so I don't know. > > [PATCH] rcu: Fix CONFIG_RCU_NOCB_CPU_ALL panic on machines with sparse CPU mask > > Some architectures have sparse cpu mask. UltraSparc's cpuinfo for example: > > CPU0: online > CPU2: online > > So, set only possible CPUs when CONFIG_RCU_NOCB_CPU_ALL is enabled. > > Also, check that user passes right 'rcu_nocbs=' option. > > Signed-off-by: Kirill Tkhai > CC: Dipankar Sarma > CC: Paul E. McKenney Queued for 3.13 with modification called out by scripts/checkpatch.pl. Please run scripts/checkpatch.pl on future patches before submitting. Thanx, Paul > --- > kernel/rcutree_plugin.h | 8 +++++++- > 1 files changed, 7 insertions(+), 1 deletions(-) > diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h > index 130c97b..0b5d673 100644 > --- a/kernel/rcutree_plugin.h > +++ b/kernel/rcutree_plugin.h > @@ -96,10 +96,16 @@ static void __init rcu_bootup_announce_oddness(void) > #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */ > #ifdef CONFIG_RCU_NOCB_CPU_ALL > pr_info("\tOffload RCU callbacks from all CPUs\n"); > - cpumask_setall(rcu_nocb_mask); > + cpumask_copy(rcu_nocb_mask, cpu_possible_mask); > #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */ > #endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */ > if (have_rcu_nocb_mask) { > + if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) { > + pr_info("\tNote: kernel parameter 'rcu_nocbs=' " > + "contains nonexistent CPUs.\n"); > + cpumask_and(rcu_nocb_mask, cpu_possible_mask, > + rcu_nocb_mask); > + } > cpulist_scnprintf(nocb_buf, sizeof(nocb_buf), rcu_nocb_mask); > pr_info("\tOffload RCU callbacks from CPUs: %s.\n", nocb_buf); > if (rcu_nocb_poll) >