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Message-ID: <cb961583-168f-6d7b-9d5b-2feb11646bcc@acm.org>
Date: Mon, 19 Jun 2017 08:31:36 -0500
From: Corey Minyard <minyard@....org>
To: Tony Camuso <tcamuso@...hat.com>,
openipmi-developer@...ts.sourceforge.net
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ipmi: use rcu lock around call to
intf->handlers->sender()
On 06/16/2017 07:15 AM, Corey Minyard wrote:
> On 06/15/2017 10:54 AM, Corey Minyard wrote:
>> On 06/13/2017 09:54 AM, Tony Camuso wrote:
>>> A vendor with a system having more than 128 CPUs occasionally
>>> encounters a
>>> crash during shutdown. This is not an easily reproduceable event,
>>> but the
>>> vendor was able to provide the following analysis of the crash, which
>>> exhibits the same footprint each time.
>>>
>>> crash> bt
>>> PID: 0 TASK: ffff88017c70ce70 CPU: 5 COMMAND: "swapper/5"
>>> #0 [ffff88085c143ac8] machine_kexec at ffffffff81059c8b
>>> #1 [ffff88085c143b28] __crash_kexec at ffffffff811052e2
>>> #2 [ffff88085c143bf8] crash_kexec at ffffffff811053d0
>>> #3 [ffff88085c143c10] oops_end at ffffffff8168ef88
>>> #4 [ffff88085c143c38] no_context at ffffffff8167ebb3
>>> #5 [ffff88085c143c88] __bad_area_nosemaphore at ffffffff8167ec49
>>> #6 [ffff88085c143cd0] bad_area_nosemaphore at ffffffff8167edb3
>>> #7 [ffff88085c143ce0] __do_page_fault at ffffffff81691d1e
>>> #8 [ffff88085c143d40] do_page_fault at ffffffff81691ec5
>>> #9 [ffff88085c143d70] page_fault at ffffffff8168e188
>>> [exception RIP: unknown or invalid address]
>>> RIP: ffffffffa053c800 RSP: ffff88085c143e28 RFLAGS: 00010206
>>> RAX: ffff88017c72bfd8 RBX: ffff88017a8dc000 RCX:
>>> ffff8810588b5ac8
>>> RDX: ffff8810588b5a00 RSI: ffffffffa053c800 RDI:
>>> ffff8810588b5a00
>>> RBP: ffff88085c143e58 R8: ffff88017c70d408 R9:
>>> ffff88017a8dc000
>>> R10: 0000000000000002 R11: ffff88085c143da0 R12:
>>> ffff8810588b5ac8
>>> R13: 0000000000000100 R14: ffffffffa053c800 R15:
>>> ffff8810588b5a00
>>> ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018
>>> --- <IRQ stack> ---
>>> [exception RIP: cpuidle_enter_state+82]
>>> RIP: ffffffff81514192 RSP: ffff88017c72be50 RFLAGS: 00000202
>>> RAX: 0000001e4c3c6f16 RBX: 000000000000f8a0 RCX:
>>> 0000000000000018
>>> RDX: 0000000225c17d03 RSI: ffff88017c72bfd8 RDI:
>>> 0000001e4c3c6f16
>>> RBP: ffff88017c72be78 R8: 000000000000237e R9:
>>> 0000000000000018
>>> R10: 0000000000002494 R11: 0000000000000001 R12:
>>> ffff88017c72be20
>>> R13: ffff88085c14f8e0 R14: 0000000000000082 R15:
>>> 0000001e4c3bb400
>>> ORIG_RAX: ffffffffffffff10 CS: 0010 SS: 0018
>>>
>>> This is the corresponding stack trace
>>>
>>> It has crashed because the area pointed with RIP extracted from timer
>>> element is already removed during a shutdown process.
>>>
>>> The function is smi_timeout().
>>>
>>> And we think ffff8810588b5a00 in RDX is a parameter struct smi_info
>>>
>>> crash> rd ffff8810588b5a00 20
>>> ffff8810588b5a00: ffff8810588b6000 0000000000000000 .`.X............
>>> ffff8810588b5a10: ffff880853264400 ffffffffa05417e0 .D&S......T.....
>>> ffff8810588b5a20: 24a024a000000000 0000000000000000 .....$.$........
>>> ffff8810588b5a30: 0000000000000000 0000000000000000 ................
>>> ffff8810588b5a40: ffffffffa053a040 ffffffffa053a060 @.S.....`.S.....
>>> ffff8810588b5a50: 0000000000000000 0000000100000001 ................
>>> ffff8810588b5a60: 0000000000000000 0000000000000e00 ................
>>> ffff8810588b5a70: ffffffffa053a580 ffffffffa053a6e0 ..S.......S.....
>>> ffff8810588b5a80: ffffffffa053a4a0 ffffffffa053a250 ..S.....P.S.....
>>> ffff8810588b5a90: 0000000500000002 0000000000000000 ................
>>>
>>> Unfortunately the top of this area is already detroyed by someone.
>>> But because of two reasonns we think this is struct smi_info
>>> 1) The address included in between ffff8810588b5a70 and
>>> ffff8810588b5a80:
>>> are inside of ipmi_si_intf.c see crash> module ffff88085779d2c0
>>>
>>> 2) We've found the area which point this.
>>> It is offset 0x68 of ffff880859df4000
>>>
>>> crash> rd ffff880859df4000 100
>>> ffff880859df4000: 0000000000000000 0000000000000001 ................
>>> ffff880859df4010: ffffffffa0535290 dead000000000200 .RS.............
>>> ffff880859df4020: ffff880859df4020 ffff880859df4020 @.Y.... @.Y....
>>> ffff880859df4030: 0000000000000002 0000000000100010 ................
>>> ffff880859df4040: ffff880859df4040 ffff880859df4040 @@.Y....@@.Y....
>>> ffff880859df4050: 0000000000000000 0000000000000000 ................
>>> ffff880859df4060: 0000000000000000 ffff8810588b5a00 .........Z.X....
>>> ffff880859df4070: 0000000000000001 ffff880859df4078 ........x@......
>>>
>>> If we regards it as struct ipmi_smi in shutdown process
>>> it looks consistent.
>>>
>>> The remedy for this apparent race is affixed below.
>>
>> I think you are right about this problem, but in_shutdown is checked
>> already
>> a bit before when newmsg is extracted from the list. Wouldn't it be
>> better
>> to add the rcu_read_lock() region starting right before the previous
>> in_shutdown check to after the send? That would avoid a leak in this
>> case.
>
> While lying awake unable to sleep, I realized that you can't call the
> sender function while holding rcu_read_lock(). That will break RT,
> because you can't claim a mutex while holding rcu_read_lock(),
> and the sender function will claim normal spinlocks.
>
> So I need to think about this a bit.
>
I was wrong about this. An rcu_read_lock() around the whole thing should
be all that is required to fix this. I can do a patch, or you can, if
you like.
Thanks again for pointing this out.
-corey
> -corey
>
>>
>> Thanks,
>>
>> -corey
>>
>>> Signed-off-by: Tony Camuso <tcamuso@...hat.com>
>>> ---
>>> drivers/char/ipmi/ipmi_msghandler.c | 9 +++++++--
>>> 1 file changed, 7 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/char/ipmi/ipmi_msghandler.c
>>> b/drivers/char/ipmi/ipmi_msghandler.c
>>> index 9f69995..577509f 100644
>>> --- a/drivers/char/ipmi/ipmi_msghandler.c
>>> +++ b/drivers/char/ipmi/ipmi_msghandler.c
>>> @@ -3897,8 +3897,13 @@ static void smi_recv_tasklet(unsigned long val)
>>> }
>>> if (!run_to_completion)
>>> spin_unlock_irqrestore(&intf->xmit_msgs_lock, flags);
>>> - if (newmsg)
>>> - intf->handlers->sender(intf->send_info, newmsg);
>>> +
>>> + if (newmsg) {
>>> + rcu_read_lock();
>>> + if (!intf->in_shutdown)
>>> + intf->handlers->sender(intf->send_info, newmsg);
>>> + rcu_read_unlock();
>>> + }
>>> handle_new_recv_msgs(intf);
>>> }
>>
>>
>
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