Message-ID: <4E25AC32.703@candelatech.com>
Date:	Tue, 19 Jul 2011 09:09:22 -0700
From:	Ben Greear <greearb@...delatech.com>
To:	paulmck@...ux.vnet.ibm.com
CC:	Peter Zijlstra <peterz@...radead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: crash in active_task, 3.0-rc6+

On 07/19/2011 07:28 AM, Paul E. McKenney wrote:
> On Tue, Jul 19, 2011 at 01:08:21PM +0200, Peter Zijlstra wrote:
>> On Mon, 2011-07-11 at 11:01 -0700, Ben Greear wrote:
>>> This is from a lightly patched kernel (nfs related patches)
>>> Same system sees lockdep warnings related to scheduling that
>>> I've been posting as well...
>>>
>>> I haven't seen anything similar in older kernels, so this may
>>> be a regression.  We tested .38 in this setup without seeing it,
>>> but havn't tested .39.
>>>
>>> [root@...ech2 ~]# BUG: unable to handle kernel NULL pointer dereference at 0000000000000004
>>> IP: [<ffffffff81231bf8>] do_raw_spin_lock+0x14/0x13c
>>> PGD 127082067 PUD 127081067 PMD 0
>>> Oops: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
>>> CPU 2
>>> Modules linked in: 8021q garp xt_addrtype xt_TPROXY nf_tproxy_core xt_socket nf_defrag_ipv6 xt_set ip_set nfnetlink xt_connlimit ip]
>>>
>>> Pid: 2203, comm: gnuserver Not tainted 3.0.0-rc6+ #20 Supermicro X7DBU/X7DBU
>>> RIP: 0010:[<ffffffff81231bf8>]  [<ffffffff81231bf8>] do_raw_spin_lock+0x14/0x13c
>>> RSP: 0018:ffff8801104e3628  EFLAGS: 00010096
>>> RAX: ffff880126b9e7e0 RBX: 0000000000000000 RCX: 0000000000000000
>>> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
>>> RBP: ffff8801104e3668 R08: 0000000000000002 R09: 0000000000000001
>>> R10: 000002bf7b96a212 R11: ffff880107481e30 R12: 0000000000000003
>>> R13: 0000000000000000 R14: 0000000000000046 R15: 0000000000000002
>>> FS:  00007f213f07c720(0000) GS:ffff88012fc80000(0000) knlGS:0000000000000000
>>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>> CR2: 0000000000000004 CR3: 0000000110519000 CR4: 00000000000006e0
>>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>>> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
>>> Process gnuserver (pid: 2203, threadinfo ffff8801104e2000, task ffff880126b9e7e0)
>>> Stack:
>>>    0000000000000018 0000000000000046 00000000bf3d0800 0000000000000000
>>>    0000000000000003 0000000000000000 0000000000000046 0000000000000002
>>>    ffff8801104e3698 ffffffff8147e459 ffffffff810a7f25 ffffffff8103d2f7
>>> Call Trace:
>>>    [<ffffffff8147e459>] _raw_spin_lock+0x3e/0x45
>>>    [<ffffffff810a7f25>] ? __rcu_read_unlock+0xdc/0x24e
>>>    [<ffffffff8103d2f7>] ? activate_task+0x30/0x30
>>>    [<ffffffff810a7f25>] __rcu_read_unlock+0xdc/0x24e
>>>    [<ffffffff8103d34d>] rcu_read_unlock+0x21/0x23
>>>    [<ffffffff8103efd7>] select_task_rq_fair+0x8cc/0x8e1
>>>    [<ffffffff81042b59>] ? finish_task_switch+0x78/0xf1
>>>    [<ffffffff81042b1b>] ? finish_task_switch+0x3a/0xf1
>>>    [<ffffffff810468d0>] ? try_to_wake_up+0x29/0x1a0
>>>    [<ffffffff810468d0>] ? try_to_wake_up+0x29/0x1a0
>>>    [<ffffffff81040c52>] select_task_rq+0x13/0x44
>>>    [<ffffffff8104697f>] try_to_wake_up+0xd8/0x1a0
>>>    [<ffffffff8103c783>] ? __wake_up+0x1d/0x48
>>>    [<ffffffff81046a54>] default_wake_function+0xd/0xf
>>>    [<ffffffff8106751a>] autoremove_wake_function+0x13/0x38
>>>    [<ffffffff810395d0>] __wake_up_common+0x49/0x7f
>>>    [<ffffffff8103c79a>] __wake_up+0x34/0x48
>>>    [<ffffffff810a74a9>] rcu_report_exp_rnp+0x50/0x89
>>>    [<ffffffff810a7f25>] ? __rcu_read_unlock+0xdc/0x24e
>>>    [<ffffffff810a8032>] __rcu_read_unlock+0x1e9/0x24e
>>>    [<ffffffff813fce40>] rcu_read_unlock+0x21/0x23
>>>    [<ffffffff813fd52d>] ip_queue_xmit+0x35e/0x3b1
>>>    [<ffffffff813fd1cf>] ? ip_send_reply+0x247/0x247
>>>    [<ffffffff8140f5f3>] tcp_transmit_skb+0x785/0x7c3
>>>    [<ffffffff81411e23>] tcp_write_xmit+0x806/0x8f5
>>>    [<ffffffff810e646f>] ? might_fault+0x4e/0x9e
>>>    [<ffffffff81403e25>] ? copy_from_user+0x2a/0x2c
>>>    [<ffffffff81411f63>] __tcp_push_pending_frames+0x20/0x4d
>>>    [<ffffffff8140411f>] tcp_push+0x84/0x86
>>>    [<ffffffff81406577>] tcp_sendmsg+0x674/0x775
>>>    [<ffffffff81423d68>] inet_sendmsg+0x61/0x6a
>>>    [<ffffffff813af67a>] __sock_sendmsg_nosec+0x58/0x61
>>>    [<ffffffff813b0db5>] __sock_sendmsg+0x3d/0x48
>>>    [<ffffffff813b1631>] sock_sendmsg+0xa3/0xbc
>>>    [<ffffffff810ea6ae>] ? handle_pte_fault+0x7fc/0x84d
>>>    [<ffffffff81110b14>] ? mem_cgroup_get_limit+0x45/0x45
>>>    [<ffffffff8111a4e9>] ? fget_light+0x35/0xac
>>>    [<ffffffff813b16b2>] ? sockfd_lookup_light+0x1b/0x53
>>>    [<ffffffff813b1bf5>] sys_sendto+0xfa/0x11f
>>>    [<ffffffff8147f0d8>] ? retint_restore_args+0x13/0x13
>>>    [<ffffffff8109f0a1>] ? audit_syscall_entry+0x119/0x145
>>>    [<ffffffff81484d52>] system_call_fastpath+0x16/0x1b
>>
>>
>> Fun, that's a recursion we've been poking at for the past few days, but
>> I haven't seen it do a NULL-ptr deref like this yet.
>>
>> I'm also not quite sure the below patches will catch this particular
>> recursion, it might be you need the patch from
>> lkml.kernel.org/r/20110718151524.GA4236@...ux.vnet.ibm.com as well,
>> since this is RCU recursing on itself without the aid of interrupts.
>>
>> How reproducable is this? And if so, what's your .config and recipe for
>> making it go bang?
>
> Yow!
>
> I bet that the .config includes CONFIG_RCU_BOOST=y.  If so, the following
> patch will be needed.  Otherwise, I have no idea how the above sequence
> of events happened -- all of the ->rcu_read_unlock_special bits should
> be cleared by the time that rcu_report_exp_rnp() is invoked.  Though
> the patch that Peter pointed you at on lkml.kernel.org above would likely
> make it go away in conjunction with the patch below.
>
> 							Thanx, Paul

Yes, I was running with boost enabled:

[greearb@fs3 linux-3.0.x64-nfs]$ grep BOOST .config
CONFIG_RCU_BOOST=y
CONFIG_RCU_BOOST_PRIO=1
CONFIG_RCU_BOOST_DELAY=500

Work load was mounting 200 nfs mounts, doing O_DIRECT io (200 processes, one per mount) for 30
seconds or so, unmount, repeat..for hours.  I could reliably crash the system on over-night
runs even after fixing the NFS bugs, but it crashed in various ways.

I'll re-run the tests with the latest upstream tree plus these patches, assuming
they are not already in the tree.  Might be a day or two, before I can get this
set up, however, as the machine in question is running some other tests on an older
kernel at the moment.

Thanks,
Ben

-- 
Ben Greear <greearb@...delatech.com>
Candela Technologies Inc  http://www.candelatech.com

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