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Message-ID: <91da06cc-3311-845e-22b6-78b69dbcdeb2@acm.org>
Date: Mon, 19 Jun 2017 09:32:16 -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 06/19/2017 09:29 AM, Tony Camuso wrote:
> On 06/19/2017 09:31 AM, Corey Minyard wrote:
>> 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
>
> Is this what you have in mind?
>
> ---
> drivers/char/ipmi/ipmi_msghandler.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/char/ipmi/ipmi_msghandler.c
> b/drivers/char/ipmi/ipmi_msghandler.c
> index 9f69995..e20f8d7 100644
> --- a/drivers/char/ipmi/ipmi_msghandler.c
> +++ b/drivers/char/ipmi/ipmi_msghandler.c
> @@ -3880,6 +3880,9 @@ static void smi_recv_tasklet(unsigned long val)
> */
> if (!run_to_completion)
> spin_lock_irqsave(&intf->xmit_msgs_lock, flags);
> +
> + rcu_read_lock();
> +
> if (intf->curr_msg == NULL && !intf->in_shutdown) {
> struct list_head *entry = NULL;
>
> @@ -3894,11 +3897,15 @@ static void smi_recv_tasklet(unsigned long val)
> newmsg = list_entry(entry, struct ipmi_smi_msg, link);
> intf->curr_msg = newmsg;
> }
> +
> + if (newmsg)
> + intf->handlers->sender(intf->send_info, newmsg);
> }
> +
> + rcu_read_unlock();
> +
> if (!run_to_completion)
> spin_unlock_irqrestore(&intf->xmit_msgs_lock, flags);
> - if (newmsg)
> - intf->handlers->sender(intf->send_info, newmsg);
>
> handle_new_recv_msgs(intf);
> }
No, you definitely cannot call the sender function while holding the lock.
I was talk about adding rcu_read_lock() before the spin_lock_irqsave()
and rcu_read_unlock() after the sender() call.
IIRC, this code was moved from a section that was under the rcu read
lock, but the lock was not added when moved.
-corey
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