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Message-ID: <1a359a04-f1da-0e2e-8663-6527e84dd5a3@acm.org>
Date: Thu, 15 Jun 2017 10:54:49 -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 06/13/2017 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.
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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