Hi, I've run into an issue where crash will enter an infinite loop while decoding exception stacks if those stacks get corrupted. We've seen this on four different systems where the hardware generated multiple NMIs and the second and subsequent NMIs caused the NMI exception stack to be overwritten. When this condition is hit, the bottom rsp on the NMI exception stack (which would normally point you back to the kernel thread stack or possibly a different exception

points you back into the middle of the same NMI exception stack. This causes crash to infinitely loop when it tries to decode that exception stack. Now clearly the root cause of the issue is faulty hardware that generated multiple NMIs. However a very small change in crash can

this issue and stop the infinite loop from happening thereby allowing you to get to a point in crash where you can actually tell that it was an NMI that caused the system to dump. The patch is attached to this email. For x86_64 it will detect the condition of any exception stack that points back at itself. Please feel free to ask me any questions on this.

-----Original Message----- From: crash-utility-bounces(a)redhat.com [mailto:crash-utility-bounces@redhat.com] On Behalf Of Dave Anderson Sent: Monday, June 28, 2010 12:11 PM To: Discussion list for crash utility usage,maintenance and development Subject: Re: [Crash-utility] infinite loop in crash due to double-NMI on x86_64 system ----- "Lucas Silacci" <Lucas.Silacci(a)teradata.com&gt; wrote: > Below is the output of running crash (with the patch) against one of > these dumps. > > -Lucas > > > crash 5.0.5 > Copyright (C) 2002-2010 Red Hat, Inc. > Copyright (C) 2004, 2005, 2006 IBM Corporation > Copyright (C) 1999-2006 Hewlett-Packard Co > Copyright (C) 2005, 2006 Fujitsu Limited > Copyright (C) 2006, 2007 VA Linux Systems Japan K.K. > Copyright (C) 2005 NEC Corporation > Copyright (C) 1999, 2002, 2007 Silicon Graphics, Inc. > Copyright (C) 1999, 2000, 2001, 2002 Mission Critical Linux, Inc. > This program is free software, covered by the GNU General Public License, > and you are welcome to change it and/or distribute copies of it under > certain conditions. Enter "help copying" to see the conditions. > > This program has absolutely no warranty. Enter "help warranty" for > details. > > GNU gdb (GDB) 7.0 > Copyright (C) 2009 Free Software Foundation, Inc. > License GPLv3+: GNU GPL version 3 or later > <http://gnu.org/licenses/gpl.html> > This is free software: you are free to change and redistribute it. > There is NO WARRANTY, to the extent permitted by law. Type "show copying" > and "show warranty" for details. > > This GDB was configured as "x86_64-unknown-linux-gnu"... > > please wait... (determining panic task) > > WARNING: Loop detected in the NMI Exception Stack! > > > bt: cannot transition from exception stack to current process stack: > exception stack pointer: ffffffff8046dc50 > process stack pointer: ffffffff8046ddd8 > current stack base: ffffffff80422000 > > SYSTEM MAP: /boot/System.map-2.6.16.53-0.8.PTF.434477.9.TDC.0-smp > DEBUG KERNEL: /boot/vmlinux-2.6.16.53-0.8.PTF.434477.9.TDC.0-smp > (2.6.16.53-0.8.PTF.434477.9.TDC.0-smp) > DUMPFILE: /var/crash/lucas.save/vmcore [PARTIAL DUMP] > CPUS: 4 > DATE: Tue May 18 12:46:07 2010 > UPTIME: 07:24:54 > LOAD AVERAGE: 85.74, 82.85, 82.29 > TASKS: 2449 > NODENAME: POLO5_1-9 > RELEASE: 2.6.16.53-0.8.PTF.434477.9.TDC.0-smp > VERSION: #1 SMP Fri Aug 31 06:07:27 PDT 2007 > MACHINE: x86_64 (2660 Mhz) > MEMORY: 7.9 GB > PANIC: "Kernel panic - not syncing: dumpsw: Dump switch pushed; reason: 0x20 args=0xffffffff8046df08" > PID: 0 > COMMAND: "swapper" > TASK: ffffffff8038c340 (1 of 4) [THREAD_INFO: ffffffff80422000] > CPU: 0 > STATE: TASK_RUNNING (PANIC) > > crash> bt > PID: 0 TASK: ffffffff8038c340 CPU: 0 COMMAND: "swapper" > #0 [ffffffff8046dc50] machine_kexec at ffffffff8011a95b > #1 [ffffffff8046dd20] crash_kexec at ffffffff80154351 > #2 [ffffffff8046dde0] panic at ffffffff801327fa > #3 [ffffffff8046ded0] dumpsw_notify at ffffffff8831c0c3 > #4 [ffffffff8046dee0] notifier_call_chain at ffffffff8032481f > #5 [ffffffff8046df00] default_do_nmi at ffffffff80322fab > #6 [ffffffff8046df40] do_nmi at ffffffff80323365 > #7 [ffffffff8046df50] nmi at ffffffff8032268f > [exception RIP: smp_send_stop+84] > RIP: ffffffff80116e44 RSP: ffffffff8046ddd8 RFLAGS: 00000246 > RAX: 00000000000000ff RBX: ffffffff8831c1f8 RCX: 000041049c7256e8 > RDX: 0000000000000005 RSI: 000000005238a938 RDI: 00000000002896a0 > RBP: ffffffff8046df08 R8: 00000000000040fb R9: 000000005238a7e8 > R10: 0000000000000002 R11: 0000ffff0000ffff R12: 000000000000000c > R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 > ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018 > --- <NMI exception stack> --- > #8 [ffffffff8046ddd8] smp_send_stop at ffffffff80116e44 > bt: WARNING: Loop detected in the NMI Exception Stack! > bt: cannot transition from exception stack to current process stack: > exception stack pointer: ffffffff8046dc50 > process stack pointer: ffffffff8046ddd8 > current stack base: ffffffff80422000 > crash> What exactly was the sequence of events? Was the system repeatedly and erroneously running one NMI after another for some reason, and *then* the "dump switch" was pressed? And the dumpsw_notify() function sends another NMI? And where does that dumpsw_notify() function live anyway? I'm just trying to get a grip on whether this will ever happen again, or whether it's fixing a one-time hardware abnormality? Dave

-----Original Message----- From: crash-utility-bounces(a)redhat.com [mailto:crash-utility-bounces@redhat.com] On Behalf Of Dave Anderson Sent: Monday, June 28, 2010 1:35 PM To: Discussion list for crash utility usage,maintenance and development Subject: Re: [Crash-utility] infinite loop in crash due to double-NMI on x86_64 system ----- "Lucas Silacci" <Lucas.Silacci(a)teradata.com&gt; wrote: > > -----Original Message----- > > From: crash-utility-bounces(a)redhat.com > > [mailto:crash-utility-bounces@redhat.com] On Behalf Of Dave > Anderson > > Sent: Monday, June 28, 2010 12:11 PM > > To: Discussion list for crash utility usage,maintenance and > > development > > Subject: Re: [Crash-utility] infinite loop in crash due to > > double-NMI on x86_64 system > > > > > > > > ----- "Lucas Silacci" <Lucas.Silacci(a)teradata.com&gt; wrote: > > > > > Below is the output of running crash (with the patch) against one > of > > > these dumps. > > > > > > -Lucas > > > > > > > > > crash 5.0.5 > > > Copyright (C) 2002-2010 Red Hat, Inc. > > > Copyright (C) 2004, 2005, 2006 IBM Corporation > > > Copyright (C) 1999-2006 Hewlett-Packard Co > > > Copyright (C) 2005, 2006 Fujitsu Limited > > > Copyright (C) 2006, 2007 VA Linux Systems Japan K.K. > > > Copyright (C) 2005 NEC Corporation > > > Copyright (C) 1999, 2002, 2007 Silicon Graphics, Inc. > > > Copyright (C) 1999, 2000, 2001, 2002 Mission Critical Linux, > Inc. > > > This program is free software, covered by the GNU General Public License, > > > and you are welcome to change it and/or distribute copies of it under > > > certain conditions. Enter "help copying" to see the conditions. > > > This program has absolutely no warranty. Enter "help warranty" for > > > details. > > > > > > GNU gdb (GDB) 7.0 > > > Copyright (C) 2009 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later > > > <http://gnu.org/licenses/gpl.html> > > > This is free software: you are free to change and redistribute it. > > > There is NO WARRANTY, to the extent permitted by law. Type "show copying" > > > and "show warranty" for details. > > > > > > This GDB was configured as "x86_64-unknown-linux-gnu"... > > > > > > please wait... (determining panic task) > > > > > > > > WARNING: Loop detected in the NMI Exception Stack! > > > > > > > > > > > bt: cannot transition from exception stack to current process > stack: > > > exception stack pointer: ffffffff8046dc50 > > > > process stack pointer: ffffffff8046ddd8 > > > current stack base: ffffffff80422000 > > > > > > SYSTEM MAP: > /boot/System.map-2.6.16.53-0.8.PTF.434477.9.TDC.0-smp > > > DEBUG KERNEL: /boot/vmlinux-2.6.16.53-0.8.PTF.434477.9.TDC.0-smp > > > (2.6.16.53-0.8.PTF.434477.9.TDC.0-smp) > > > DUMPFILE: /var/crash/lucas.save/vmcore [PARTIAL DUMP] > > > CPUS: 4 > > > DATE: Tue May 18 12:46:07 2010 > > > UPTIME: 07:24:54 > > > LOAD AVERAGE: 85.74, 82.85, 82.29 > > > TASKS: 2449 > > > NODENAME: POLO5_1-9 > > > RELEASE: 2.6.16.53-0.8.PTF.434477.9.TDC.0-smp > > > VERSION: #1 SMP Fri Aug 31 06:07:27 PDT 2007 > > > MACHINE: x86_64 (2660 Mhz) > > > MEMORY: 7.9 GB > > > PANIC: "Kernel panic - not syncing: dumpsw: Dump > > switch pushed; reason: 0x20 args=0xffffffff8046df08" > > > PID: 0 > > > COMMAND: "swapper" > > > TASK: ffffffff8038c340 (1 of 4) [THREAD_INFO: > > ffffffff80422000] > > > CPU: 0 > > > STATE: TASK_RUNNING (PANIC) > > > > > > crash> bt > > > PID: 0 TASK: ffffffff8038c340 CPU: 0 COMMAND: "swapper" > > > #0 [ffffffff8046dc50] machine_kexec at ffffffff8011a95b > > > #1 [ffffffff8046dd20] crash_kexec at ffffffff80154351 > > > #2 [ffffffff8046dde0] panic at ffffffff801327fa > > > #3 [ffffffff8046ded0] dumpsw_notify at ffffffff8831c0c3 > > > #4 [ffffffff8046dee0] notifier_call_chain at ffffffff8032481f > > > #5 [ffffffff8046df00] default_do_nmi at ffffffff80322fab > > > #6 [ffffffff8046df40] do_nmi at ffffffff80323365 > > > #7 [ffffffff8046df50] nmi at ffffffff8032268f > > > [exception RIP: smp_send_stop+84] > > > RIP: ffffffff80116e44 RSP: ffffffff8046ddd8 RFLAGS: > 00000246 > > > RAX: 00000000000000ff RBX: ffffffff8831c1f8 RCX: > > 000041049c7256e8 > > > RDX: 0000000000000005 RSI: 000000005238a938 RDI: > > 00000000002896a0 > > > RBP: ffffffff8046df08 R8: 00000000000040fb R9: > > 000000005238a7e8 > > > R10: 0000000000000002 R11: 0000ffff0000ffff R12: > > 000000000000000c > > > R13: 0000000000000000 R14: 0000000000000000 R15: > > 0000000000000000 > > > ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018 > > > --- <NMI exception stack> --- > > > #8 [ffffffff8046ddd8] smp_send_stop at ffffffff80116e44 > > > bt: WARNING: Loop detected in the NMI Exception Stack! > > > bt: cannot transition from exception stack to current process > stack: > > > exception stack pointer: ffffffff8046dc50 > > > process stack pointer: ffffffff8046ddd8 > > > current stack base: ffffffff80422000 > > > crash> > > > > What exactly was the sequence of events? Was the system repeatedly and > > erroneously running one NMI after another for some reason, and *then* the > > "dump switch" was pressed? And the dumpsw_notify() function sends another > > NMI? And where does that dumpsw_notify() function live anyway? > > > > I'm just trying to get a grip on whether this will ever happen again, or > > whether it's fixing a one-time hardware abnormality? > > > > Dave > > > > As far as I am aware, we have had three separate customers encounter > this issue. It appears from the hardware SEL log that multiple PCI > SERR's came in at the same time and somehow triggered multiple NMIs. > You can see the SEL entries from the output of the "ipmitool sel" > command: > > 0231 11FC 02 01:53:47 12/17/09 3300 04 13 EB 6F A5 15 08 > Crit. > Interrupt PCI SERR (PCI Bus 15 Device 1 Function 0) was asserted > 0232 1210 02 01:53:47 12/17/09 3300 04 13 EB 6F A5 16 20 > Crit. > Interrupt PCI SERR (PCI Bus 16 Device 4 Function 0) was asserted > 0233 1224 02 01:53:47 12/17/09 3300 04 13 EB 6F A5 16 21 > Crit. > Interrupt PCI SERR (PCI Bus 16 Device 4 Function 1) was asserted > 0234 1238 02 01:53:47 12/17/09 3300 04 13 EB 6F A5 16 30 > Crit. > Interrupt PCI SERR (PCI Bus 16 Device 6 Function 0) was asserted > 0235 124C 02 01:53:47 12/17/09 3300 04 13 EB 6F A5 16 31 > Crit. > Interrupt PCI SERR (PCI Bus 16 Device 6 Function 1) was asserted > > My understanding of the architecture of the system is that only one NMI > should have been asserted to the OS regardless of the number of times > there was a hardware error, but clearly that wasn't the case in these > three instances. > > Also, it seemed like my patch made crash a little bit more tolerant of > "corrupted" dump images which I thought could only be a good thing. Right, I understand that... But you didn't answer my questions re: the "dump switch" procedure and the dumpsw_notify() function. Was the system stuck in the NMI handler, somebody noticed the repetetive NMIs (?), and so they hit the "dump switch"? (whatever that may be...) Dave -- Crash-utility mailing list Crash-utility(a)redhat.com https://www.redhat.com/mailman/listinfo/crash-utility