rpms/kernel
3
0
Fork 0
Code Issues Pull Requests Releases Wiki Activity

silence another rcu_reference warning

Browse Source
This commit is contained in:
Dave Jones 2010-09-30 15:57:12 -04:00
parent a1ae900880
commit e67d8276aa
2 changed files with 223 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
kernel.spec
View File

@ -681,6 +681,8 @@ Patch2912: linux-2.6-v4l-dvb-ir-core-update.patch
#Patch2916: lirc-staging-2.6.36-fixes.patch
Patch2917: hdpvr-ir-enable.patch
Patch3000: linux-2.6-rcu-sched-warning.patch
# fs fixes
# NFSv4
@ -1293,6 +1295,9 @@ ApplyOptionalPatch linux-2.6-v4l-dvb-experimental.patch
# enable IR receiver on Hauppauge HD PVR (v4l-dvb merge pending)
ApplyPatch hdpvr-ir-enable.patch
# silence another rcu_reference warning
ApplyPatch linux-2.6-rcu-sched-warning.patch
# Patches headed upstream
ApplyPatch disable-i8042-check-on-apple-mac.patch
@ -1939,6 +1944,9 @@ fi
# || ||
%changelog
* Thu Sep 30 2010 Dave Jones <davej@redhat.com>
- silence another rcu_reference warning
* Thu Sep 30 2010 Kyle McMartin <kyle@redhat.com> 2.6.36-0.30.rc6
- Collection of patches to make intel_ips work properly.

215
linux-2.6-rcu-sched-warning.patch Normal file
View File

@ -0,0 +1,215 @@
From davej Thu Sep 16 11:55:58 2010
Return-Path: linux-kernel-owner@vger.kernel.org
X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on gelk
X-Spam-Level:
X-Spam-Status: No, score=-4.2 required=5.0 tests=BAYES_00,RCVD_IN_DNSWL_MED,
T_RP_MATCHES_RCVD,UNPARSEABLE_RELAY autolearn=ham version=3.3.1
Received: from mail.corp.redhat.com [10.5.5.52]
by gelk with IMAP (fetchmail-6.3.17)
for <davej@localhost> (single-drop); Thu, 16 Sep 2010 11:55:58 -0400 (EDT)
Received: from zmta02.collab.prod.int.phx2.redhat.com (LHLO
zmta02.collab.prod.int.phx2.redhat.com) (10.5.5.32) by
mail04.corp.redhat.com with LMTP; Thu, 16 Sep 2010 11:51:27 -0400 (EDT)
Received: from localhost (localhost.localdomain [127.0.0.1])
by zmta02.collab.prod.int.phx2.redhat.com (Postfix) with ESMTP id 4889C9FC56;
Thu, 16 Sep 2010 11:51:27 -0400 (EDT)
Received: from zmta02.collab.prod.int.phx2.redhat.com ([127.0.0.1])
by localhost (zmta02.collab.prod.int.phx2.redhat.com [127.0.0.1]) (amavisd-new, port 10024)
with ESMTP id 94mQrmwfCpY4; Thu, 16 Sep 2010 11:51:27 -0400 (EDT)
Received: from int-mx03.intmail.prod.int.phx2.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.16])
by zmta02.collab.prod.int.phx2.redhat.com (Postfix) with ESMTP id 0DBDB9FC4B;
Thu, 16 Sep 2010 11:51:27 -0400 (EDT)
Received: from mx1.redhat.com (ext-mx05.extmail.prod.ext.phx2.redhat.com [10.5.110.9])
by int-mx03.intmail.prod.int.phx2.redhat.com (8.13.8/8.13.8) with ESMTP id o8GFpQnO003857;
Thu, 16 Sep 2010 11:51:26 -0400
Received: from vger.kernel.org (vger.kernel.org [209.132.180.67])
by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id o8GFFCFE031066;
Thu, 16 Sep 2010 11:51:17 -0400
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
id S1755493Ab0IPPvH (ORCPT <rfc822;jasowang@redhat.com> + 41 others);
Thu, 16 Sep 2010 11:51:07 -0400
Received: from casper.infradead.org ([85.118.1.10]:41834 "EHLO
casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
with ESMTP id S1754921Ab0IPPvC convert rfc822-to-8bit (ORCPT
<rfc822;linux-kernel@vger.kernel.org>);
Thu, 16 Sep 2010 11:51:02 -0400
Received: from f199130.upc-f.chello.nl ([80.56.199.130] helo=laptop)
by casper.infradead.org with esmtpsa (Exim 4.72 #1 (Red Hat Linux))
id 1OwGjI-0003VE-Ux; Thu, 16 Sep 2010 15:50:33 +0000
Received: by laptop (Postfix, from userid 1000)
id 6DCDB100AEB1D; Thu, 16 Sep 2010 17:50:32 +0200 (CEST)
Subject: Re: 2.6.35-stable/ppc64/p7: suspicious rcu_dereference_check()
usage detected during 2.6.35-stable boot
From: Peter Zijlstra <peterz@infradead.org>
To: paulmck@linux.vnet.ibm.com
Cc: Subrata Modak <subrata@linux.vnet.ibm.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
Li Zefan <lizf@cn.fujitsu.com>, Linuxppc-dev <Linuxppc-dev@ozlabs.org>,
sachinp <sachinp@linux.vnet.ibm.com>,
DIVYA PRAKASH <dipraksh@linux.vnet.ibm.com>,
"Valdis.Kletnieks" <Valdis.Kletnieks@vt.edu>
In-Reply-To: <20100809161200.GC3026@linux.vnet.ibm.com>
References: <1280739132.15317.9.camel@subratamodak.linux.ibm.com>
<20100809161200.GC3026@linux.vnet.ibm.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 8BIT
Date: Thu, 16 Sep 2010 17:50:31 +0200
Message-ID: <1284652231.2275.569.camel@laptop>
Mime-Version: 1.0
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
X-RedHat-Spam-Score: -2.31 (RCVD_IN_DNSWL_MED,T_RP_MATCHES_RCVD)
X-Scanned-By: MIMEDefang 2.67 on 10.5.11.16
X-Scanned-By: MIMEDefang 2.67 on 10.5.110.9
Status: RO
Content-Length: 6752
Lines: 145
On Mon, 2010-08-09 at 09:12 -0700, Paul E. McKenney wrote:
> > [ 0.051203] CPU0: AMD QEMU Virtual CPU version 0.12.4 stepping 03
> > [ 0.052999] lockdep: fixing up alternatives.
> > [ 0.054105]
> > [ 0.054106] ===================================================
> > [ 0.054999] [ INFO: suspicious rcu_dereference_check() usage. ]
> > [ 0.054999] ---------------------------------------------------
> > [ 0.054999] kernel/sched.c:616 invoked rcu_dereference_check() without protection!
> > [ 0.054999]
> > [ 0.054999] other info that might help us debug this:
> > [ 0.054999]
> > [ 0.054999]
> > [ 0.054999] rcu_scheduler_active = 1, debug_locks = 1
> > [ 0.054999] 3 locks held by swapper/1:
> > [ 0.054999] #0: (cpu_add_remove_lock){+.+.+.}, at: [<ffffffff814be933>] cpu_up+0x42/0x6a
> > [ 0.054999] #1: (cpu_hotplug.lock){+.+.+.}, at: [<ffffffff810400d8>] cpu_hotplug_begin+0x2a/0x51
> > [ 0.054999] #2: (&rq->lock){-.-...}, at: [<ffffffff814be2f7>] init_idle+0x2f/0x113
> > [ 0.054999]
> > [ 0.054999] stack backtrace:
> > [ 0.054999] Pid: 1, comm: swapper Not tainted 2.6.35 #1
> > [ 0.054999] Call Trace:
> > [ 0.054999] [<ffffffff81068054>] lockdep_rcu_dereference+0x9b/0xa3
> > [ 0.054999] [<ffffffff810325c3>] task_group+0x7b/0x8a
> > [ 0.054999] [<ffffffff810325e5>] set_task_rq+0x13/0x40
> > [ 0.054999] [<ffffffff814be39a>] init_idle+0xd2/0x113
> > [ 0.054999] [<ffffffff814be78a>] fork_idle+0xb8/0xc7
> > [ 0.054999] [<ffffffff81068717>] ? mark_held_locks+0x4d/0x6b
> > [ 0.054999] [<ffffffff814bcebd>] do_fork_idle+0x17/0x2b
> > [ 0.054999] [<ffffffff814bc89b>] native_cpu_up+0x1c1/0x724
> > [ 0.054999] [<ffffffff814bcea6>] ? do_fork_idle+0x0/0x2b
> > [ 0.054999] [<ffffffff814be876>] _cpu_up+0xac/0x127
> > [ 0.054999] [<ffffffff814be946>] cpu_up+0x55/0x6a
> > [ 0.054999] [<ffffffff81ab562a>] kernel_init+0xe1/0x1ff
> > [ 0.054999] [<ffffffff81003854>] kernel_thread_helper+0x4/0x10
> > [ 0.054999] [<ffffffff814c353c>] ? restore_args+0x0/0x30
> > [ 0.054999] [<ffffffff81ab5549>] ? kernel_init+0x0/0x1ff
> > [ 0.054999] [<ffffffff81003850>] ? kernel_thread_helper+0x0/0x10
> > [ 0.056074] Booting Node 0, Processors #1lockdep: fixing up alternatives.
> > [ 0.130045] #2lockdep: fixing up alternatives.
> > [ 0.203089] #3 Ok.
> > [ 0.275286] Brought up 4 CPUs
> > [ 0.276005] Total of 4 processors activated (16017.17 BogoMIPS).
>
> This does look like a new one, thank you for reporting it!
>
> Here is my analysis, which should at least provide some humor value to
> those who understand the code better than I do. ;-)
>
> So the corresponding rcu_dereference_check() is in
> task_subsys_state_check(), and is fetching the cpu_cgroup_subsys_id
> element of the newly created task's task->cgroups->subsys[] array.
> The "git grep" command finds only three uses of cpu_cgroup_subsys_id,
> but no definition.
>
> Now, fork_idle() invokes copy_process(), which invokes cgroup_fork(),
> which sets the child process's ->cgroups pointer to that of the parent,
> also invoking get_css_set(), which increments the corresponding reference
> count, doing both operations under task_lock() protection (->alloc_lock).
> Because fork_idle() does not specify any of CLONE_NEWNS, CLONE_NEWUTS,
> CLONE_NEWIPC, CLONE_NEWPID, or CLONE_NEWNET, copy_namespaces() should
> not create a new namespace, and so there should be no ns_cgroup_clone().
> We should thus retain the parent's ->cgroups pointer. And copy_process()
> installs the new task in the various lists, so that the task is externally
> accessible upon return.
>
> After a non-error return from copy_process(), fork_init() invokes
> init_idle_pid(), which does not appear to affect the task's cgroup
> state. Next fork_init() invokes init_idle(), which in turn invokes
> __set_task_cpu(), which invokes set_task_rq(), which calls task_group()
> several times, which calls task_subsys_state_check(), which calls the
> rcu_dereference_check() that complained above.
>
> However, the result returns by rcu_dereference_check() is stored into
> the task structure:
>
> p->se.cfs_rq = task_group(p)->cfs_rq[cpu];
> p->se.parent = task_group(p)->se[cpu];
>
> This means that the corresponding structure must have been tied down with
> a reference count or some such. If such a reference has been taken, then
> this complaint is a false positive, and could be suppressed by putting
> rcu_read_lock() and rcu_read_unlock() around the call to init_idle()
> from fork_idle(). However, although, reference to the enclosing ->cgroups
> struct css_set is held, it is not clear to me that this reference applies
> to the structures pointed to by the ->subsys[] array, especially given
> that the cgroup_subsys_state structures referenced by this array have
> their own reference count, which does not appear to me to be acquired
> by this code path.
>
> Or are the cgroup_subsys_state structures referenced by idle tasks
> never freed or some such?
I would hope so!, the idle tasks should be part of the root cgroup,
which is not removable.
The problem is that while we do in-fact hold rq->lock, the newly spawned
idle thread's cpu is not yet set to the correct cpu so the lockdep check
in task_group():
lockdep_is_held(&task_rq(p)->lock)
will fail.
But of a chicken and egg problem. Setting the cpu needs to have the cpu
set ;-)
Ingo, why do we have rq->lock there at all? The CPU isn't up and running
yet, nothing should be touching it.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
kernel/sched.c | 12 ++++++++++++
1 files changed, 12 insertions(+), 0 deletions(-)
diff --git a/kernel/sched.c b/kernel/sched.c
index bd8b487..6241049 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5332,7 +5332,19 @@ void __cpuinit init_idle(struct task_struct *idle, int cpu)
idle->se.exec_start = sched_clock();
cpumask_copy(&idle->cpus_allowed, cpumask_of(cpu));
+ /*
+ * We're having a chicken and egg problem, even though we are
+ * holding rq->lock, the cpu isn't yet set to this cpu so the
+ * lockdep check in task_group() will fail.
+ *
+ * Similar case to sched_fork(). / Alternatively we could
+ * use task_rq_lock() here and obtain the other rq->lock.
+ *
+ * Silence PROVE_RCU
+ */
+ rcu_read_lock();
__set_task_cpu(idle, cpu);
+ rcu_read_unlock();
rq->curr = rq->idle = idle;
#if defined(CONFIG_SMP) && defined(__ARCH_WANT_UNLOCKED_CTXSW)
--
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/