Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751628AbdFOPyz (ORCPT ); Thu, 15 Jun 2017 11:54:55 -0400 Received: from mail-pg0-f68.google.com ([74.125.83.68]:33149 "EHLO mail-pg0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750727AbdFOPyx (ORCPT ); Thu, 15 Jun 2017 11:54:53 -0400 Reply-To: minyard@acm.org Subject: Re: [PATCH] ipmi: use rcu lock around call to intf->handlers->sender() To: Tony Camuso , openipmi-developer@lists.sourceforge.net Cc: linux-kernel@vger.kernel.org References: <1497365651-7413-1-git-send-email-tcamuso@redhat.com> From: Corey Minyard Message-ID: <1a359a04-f1da-0e2e-8663-6527e84dd5a3@acm.org> Date: Thu, 15 Jun 2017 10:54:49 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.1 MIME-Version: 1.0 In-Reply-To: <1497365651-7413-1-git-send-email-tcamuso@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-GB Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5445 Lines: 116 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 > --- --- > [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@.Y.... > > 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 > --- > 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); > }