Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751062AbdFSOmo (ORCPT ); Mon, 19 Jun 2017 10:42:44 -0400 Received: from mx1.redhat.com ([209.132.183.28]:6937 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750761AbdFSOmm (ORCPT ); Mon, 19 Jun 2017 10:42:42 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 69207C060216 Authentication-Results: ext-mx08.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx08.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=tcamuso@redhat.com DKIM-Filter: OpenDKIM Filter v2.11.0 mx1.redhat.com 69207C060216 Subject: Re: [PATCH] ipmi: use rcu lock around call to intf->handlers->sender() To: minyard@acm.org, 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>

<91da06cc-3311-845e-22b6-78b69dbcdeb2@acm.org> From: Tony Camuso Message-ID: Date: Mon, 19 Jun 2017 10:42:41 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.0 MIME-Version: 1.0 In-Reply-To: <91da06cc-3311-845e-22b6-78b69dbcdeb2@acm.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Mon, 19 Jun 2017 14:42:42 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 8151 Lines: 181 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 >>>>>> --- --- >>>>>> [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. 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 >