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Date: Mon, 19 Jun 2017 10:42:41 -0400
From: Tony Camuso <tcamuso@...hat.com>
To: minyard@....org, 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 10:32 AM, Corey Minyard wrote:
> 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.
More like this, then.
diff --git a/drivers/char/ipmi/ipmi_msghandler.c b/drivers/char/ipmi/ipmi_msghandler.c
index 9f69995..49a7e96 100644
--- a/drivers/char/ipmi/ipmi_msghandler.c
+++ b/drivers/char/ipmi/ipmi_msghandler.c
@@ -3878,6 +3878,9 @@ static void smi_recv_tasklet(unsigned long val)
* because the lower layer is allowed to hold locks while calling
* message delivery.
*/
+
+ rcu_read_lock();
+
if (!run_to_completion)
spin_lock_irqsave(&intf->xmit_msgs_lock, flags);
if (intf->curr_msg == NULL && !intf->in_shutdown) {
@@ -3900,6 +3903,8 @@ static void smi_recv_tasklet(unsigned long val)
if (newmsg)
intf->handlers->sender(intf->send_info, newmsg);
+ rcu_read_unlock();
+
handle_new_recv_msgs(intf);
}
>
> 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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