[logger] Fix Kernel GP seen for any short-lived *syncd process

[vaibhavhd]

Fixes: sonic-net/sonic-buildimage#6103

This PR is to fix the Kernel GP errors that are seen in any short-lived process within swss.

As part of *syncd initialization, Logger::linkToDbNative function is called. This call starts a SettingThread in the background.
When the main *syncd process terminates the destructor Logger::~Logger simply detaches the SettingThread. This leads to the detached thread's continued exection in the background.

At the same time, the exiting main process deletes the static variables that were in its scope.
Fault is hit when the detached thread (still executing in the infinite loop) tries to access these freed up variables.

This issue is easily reproducible when these *syncd process are short lived (and the detached SettingThread is still executing). Below are the examples by simply executing the help option:

Sample 1 : Orchagent core and Kernel GP:

for i in {1..10}; do docker exec -it swss /usr/bin/orchagent -h  ; done

Jan 11 23:32:50.690125 str-s6100-acs-2 INFO kernel: [ 1198.660072] traps: orchagent[6172] general protection ip:7fda4ccf34fa sp:7fda4c0eb210 error:0 in libswsscommon.so.0.0.0[7fda4cccf000+5b000]
Jan 11 23:32:59.810183 str-s6100-acs-2 INFO kernel: [ 1207.781516] traps: orchagent[7380] general protection ip:7f2bfd3724fa sp:7f2bfc76a210 error:0 in libswsscommon.so.0.0.0[7f2bfd34e000+5b000]

-rw-rw-rw- 1 root root 331K Jan 11 23:32 orchagent.1610407968.6463.core.gz

Sample 2 : Gearsyncd core and Kernel GP:

for i in {1..10}; do docker exec -it swss /usr/bin/gearsyncd -h  ; done

Jan 11 23:22:40.959207 str-s6100-acs-2 INFO kernel: [  588.941879] traps: gearsyncd[25118] general protection ip:7f5e3ec924fa sp:7f5e3e706690 error:0 in libswsscommon.so.0.0.0[7f5e3ec6e000+5b000]
Jan 11 23:22:41.426841 str-s6100-acs-2 INFO kernel: [  589.409417] traps: gearsyncd[25188] general protection ip:7f35fd1504fa sp:7f35fcbc49b0 error:0 in libswsscommon.so.0.0.0[7f35fd12c000+5b000]

-rw-rw-rw- 1 root root 142K Jan 11 23:20 gearsyncd.1610407223.879.core.gz

Sample 3 : portsyncd core and Kernel GP:

for i in {1..10}; do docker exec -it swss /usr/bin/portsyncd -h  ; done

Jan 11 23:19:53.478111 str-s6100-acs-2 INFO kernel: [  421.443939] traps: portsyncd[6052] general protection ip:7f36b47714fa sp:7f36b41e59b0 error:0 in libswsscommon.so.0.0.0[7f36b474d000+5b000]
Jan 11 23:19:54.570082 str-s6100-acs-2 INFO kernel: [  422.536931] traps: portsyncd[6207] general protection ip:7f9e208ce4fa sp:7f9e203429b0 error:0 in libswsscommon.so.0.0.0[7f9e208aa000+5b000]

-rw-rw-rw- 1 root root 144K Jan 11 23:20 portsyncd.1610407201.848.core.gz

Fix:

1. Before exiting the main process, set the flag in Logger destructor to signal the detached thread that the main process is finishing up.
2. Instead of detaching the thread (which leaves this thread access the undefined static variables), join the SettingThread thread.

[qiluo-msft]

Add volatile #Closed

[vaibhavhd]

Updated to volatile

[qiluo-msft]

In the title, could you talk with the context of logger?