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Cisco Bug: CSCub38654 - N5K: Switch hang/lock up may occur due to Leap second update

Last Modified

Mar 26, 2018

Products (6)

  • Cisco Nexus 5000 Series Switches
  • Cisco Nexus 5596UP Switch
  • Cisco Nexus 5548P Switch
  • Cisco Nexus 5020 Switch
  • Cisco Nexus 5548UP Switch
  • Cisco Nexus 5010 Switch

Known Affected Releases

5.1(3)N2(1c) 5.2(8)N1(1)

Description (partial)

Symptom:
There are periodic leap second events which can add or delete a second to global time. 

When the leap second update occurs N5K NX-OS 5.0, 5.1 5.2 versions run an affected version of the Linux kernel. A Nexus 5010/5500 running affected code could experience a lock up condition. 

If the N5K was stuck in hung state, mgmt0, in band management will not be possible. On console messages such as following will be seen

Setting: rc 5 BUG: spinlock lockup on CPU#0, adj_x86s.bin/5926, lock=c793a6e0 pc=c013c560

SMI: System watchdog timed out
NXOS_WATCHDOG: ffff [#1] SMP 
Cpu: 0 Watchdog timer NMI occurred (0)
SMI: System watchdog timed out
SMI: System watchdog timed out


If switch is hung in this state, the switch will need to be manually power cycled to recover.

Conditions:
With this issue in the Kernel Nexus 50x0/55xx running affected NX-OS may hit what is known as a kernel "livelock"  under the following conditions:

  a. When the NTP server pushes the update to the N5K NTPd client, which in turn schedules the update 
       to the Kernel. This push should have happened 24 hours before June 30th, by most NTP servers.
  b. When the NTP server actually updates the clock.
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