Description

This article explains about the following error message:

kernel: jlock (W) hog reported: jlock acquired for 547 msecs: thread 0xfffff800c2711560 (sshd): offending fn tcp_usr_send() (../../../../../../../../../src/junos/bsd/sys/netinet/tcp_usrreq.c, line 1168): { 0xffffffff80ea626c 0xffffffff80ea8b4a 0xffffffff810cb4b6 0xffffffff80e9edd5 0xffffffff80491942 0xffffffff8048a147 0xffffffff80489cfb 0xffffffff80584b58 0xffffffff8056b71b }. nvcsw 0, nivcsw 4.

Symptoms

1) The device reports the following Log message:

kernel: jlock (W) hog reported: jlock acquired for 547 msecs: thread 0xfffff800c2711560 (sshd): offending fn tcp_usr_send() (../../../../../../../../../src/junos/bsd/sys/netinet/tcp_usrreq.c, line 1168): { 0xffffffff80ea626c 0xffffffff80ea8b4a 0xffffffff810cb4b6 0xffffffff80e9edd5 0xffffffff80491942 0xffffffff8048a147 0xffffffff80489cfb 0xffffffff80584b58 0xffffffff8056b71b }. nvcsw 0, nivcsw 4.

2) No alarms nor core-dumps may be found.

3) There might be other error messages reported along with the jlock hog messages.

Solution

1) JHOG Error or Jlock hog error is a synchronization mechanism to limit the access when there are many threads of execution, the jlock hog may happen if some applications have not released the lock for a long duration. 

2) In the below example, the jlock hog reported for 547 milliseconds is an informative message. This is related to tcp session function offending fn tcp_usr_send() which has take more cpu cycles than 500msec thus this message.

kernel: jlock (W) hog reported: jlock acquired for 547 msecs: thread 0xfffff800c2711560 (sshd): offending fn tcp_usr_send() (../../../../../../../../../src/junos/bsd/sys/netinet/tcp_usrreq.c, line 1168): { 0xffffffff80ea626c 0xffffffff80ea8b4a 0xffffffff810cb4b6 0xffffffff80e9edd5 0xffffffff80491942 0xffffffff8048a147 0xffffffff80489cfb 0xffffffff80584b58 0xffffffff8056b71b }. nvcsw 0, nivcsw 4.

3) If the jlock hog message do not repeat and it is just a single occurrence, this can be ignored. There shouldn't be any traffic impact.

4) If the messages repeat multiple times, check for the Error message that is reported around the time the jlock message got logged. And please contact JTAC support for further analysis on the error logs.
 

Modification History

2024-06-07 : Article Created