Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751762AbdFSOc1 (ORCPT ); Mon, 19 Jun 2017 10:32:27 -0400 Received: from mail-pg0-f67.google.com ([74.125.83.67]:35962 "EHLO mail-pg0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750950AbdFSOcZ (ORCPT ); Mon, 19 Jun 2017 10:32:25 -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> <1a359a04-f1da-0e2e-8663-6527e84dd5a3@acm.org> <613dc158-e3de-f713-019e-cf8c190e72be@acm.org>

From: Corey Minyard Message-ID: <91da06cc-3311-845e-22b6-78b69dbcdeb2@acm.org> Date: Mon, 19 Jun 2017 09:32:16 -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: 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: 7300 Lines: 171 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 >>>>> --- --- >>>>> [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. >>> >>> 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