Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753328AbdFPMPH (ORCPT ); Fri, 16 Jun 2017 08:15:07 -0400 Received: from mail-pg0-f65.google.com ([74.125.83.65]:35530 "EHLO mail-pg0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752566AbdFPMPG (ORCPT ); Fri, 16 Jun 2017 08:15:06 -0400 Reply-To: minyard@acm.org Subject: Re: [PATCH] ipmi: use rcu lock around call to intf->handlers->sender() From: Corey Minyard 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> Message-ID: <613dc158-e3de-f713-019e-cf8c190e72be@acm.org> Date: Fri, 16 Jun 2017 07:15:00 -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: <1a359a04-f1da-0e2e-8663-6527e84dd5a3@acm.org> 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: 5959 Lines: 133 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. -corey > > 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); >> } > >