[Bug 1073478] Re: [SRU] Update squid3 upstart script to kill it with SIGINT and wait longer

Michael Terry michael.terry at canonical.com
Wed Oct 14 16:38:12 UTC 2015


** Also affects: squid3 (Ubuntu Precise)
   Importance: Undecided
       Status: New

** Also affects: squid3 (Ubuntu Trusty)
   Importance: Undecided
       Status: New

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Title:
  [SRU] Update squid3 upstart script to kill it with SIGINT and wait
  longer

Status in squid3 package in Ubuntu:
  Triaged
Status in squid3 source package in Precise:
  New
Status in squid3 source package in Trusty:
  New

Bug description:
  [Impact]

  Squid 3.1.19-1ubuntu3.12.04.3 on Precise and 3.3.8-1ubuntu6.3 on
  Trusty do not clean up its PID file, causing logrotate to spit out an
  error each night when cron runs it.

  The underlying issue here is that the upstart script does not wait
  long enough for squid3 to finish - one might also argue that it is
  using the wrong signal if it expects squid to finish quickly.

  By default, when squid3 receives a SIGTERM it will close the socket
  for incoming connections and will wait for existing connections to
  complete. The shutdown_lifetime directive configures how long it waits
  before forcefully closing those open connections and it is set by
  default to 30 seconds.

  Current setting, SIGKILL happens after 5 seconds (which is the upstart default):
  =====
  # strace -r -e trace=signal,file -p $(cat /var/run/squid3.pid)
  Process 20865 attached - interrupt to quit
       0.000000 --- SIGTERM (Terminated) @ 0 (0) ---
       0.000440 rt_sigreturn(0xf) = -1 EINTR (Interrupted system call)
       0.000418 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=118, ...}) = 0
       5.006483 +++ killed by SIGKILL +++

  Killing squid with SIGKILL might lead to cache index corruption and a
  very slow startup the next time it is started: http://lists.squid-
  cache.org/pipermail/squid-users/2015-July/004752.html

  The first way to avoid this is by increasing upstart's "kill timeout"
  to a few seconds more then the "shutdown_lifetime" directive.

  With "kill timeout 40" in upstart script, notice the pid file being unlinked (the ~30 seconds wait is due to the default value of shutdown_lifetime directive):
  =====
  # strace -r -e trace=signal,file -p $(cat /var/run/squid3.pid)
  Process 20805 attached - interrupt to quit
       0.000000 --- SIGTERM (Terminated) @ 0 (0) ---
       0.000284 rt_sigreturn(0xf) = -1 EINTR (Interrupted system call)
       0.000402 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=118, ...}) = 0
      31.611726 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=118, ...}) = 0
       0.001792 --- SIGCHLD (Child exited) @ 0 (0) ---
       0.000247 rt_sigreturn(0xffffffffffffffff) = 63
       0.006027 unlink("/var/run/squid3.pid") = 0
       0.000539 open("/proc/sys/kernel/ngroups_max", O_RDONLY) = 0
       0.000387 open("/etc/group", O_RDONLY|O_CLOEXEC) = 0
  Process 20805 detached

  Still, this will unfortunately lead to a slow shutdown time as
  reported in http://askubuntu.com/questions/18127/squid3-starts-and-
  stops-slowly

  To solve this it is better to issue a SIGINT instead of SIGTERM
  (upstart default) by adding "kill signal SIGINT" to squid's upstart
  script.

  With "kill signal SIGINT", which does not wait on outstanding connections:
  =====
  # strace -r -e trace=signal,file -p $(cat /var/run/squid3.pid)
  Process 20891 attached - interrupt to quit
       0.000000 --- SIGINT (Interrupt) @ 0 (0) ---
       0.000312 rt_sigreturn(0x2) = -1 EINTR (Interrupted system call)
       0.000237 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=118, ...}) = 0
       1.123564 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=118, ...}) = 0
       0.000754 --- SIGCHLD (Child exited) @ 0 (0) ---
       0.000103 rt_sigreturn(0xffffffffffffffff) = 0
       0.002031 unlink("/var/run/squid3.pid") = 0
       0.000154 open("/proc/sys/kernel/ngroups_max", O_RDONLY) = 0
       0.000142 open("/etc/group", O_RDONLY|O_CLOEXEC) = 0
  Process 20891 detached

  The whole stop process is very quick. The downside is that squid will
  forcefully close all open connections immediately, but that was
  already happening when SIGKILL was being issued before - so we are
  actually keeping the same behavior as before and there are no bugs
  complaining about it. And the PID file gets removed anyway.

  The proposal is to add both "kill signal SIGINT" and "kill timeout 40"
  to squid, so squid should have enough time to close all open cache
  index files.

  [Test Case]

  # start squid3
  squid3 start/running, process 10392
  # cat /var/run/squid3.pid
  10392
  # stop squid3
  squid3 stop/waiting
  # cat /var/run/squid3.pid
  10392
  # logrotate -f /etc/logrotate.d/squid3
  squid: ERROR: Could not send signal 10 to process 10392: (3) No such process
  error: error running shared postrotate script for '/var/log/squid3/*.log '

  [Regression Potential]

  * The main regression potencial is related to the "kill timeout" value. If set too high, a user's system might *seem* too slow to shutdown. Note that this should rarely happen: only when squid actually needs a long time to write down and close its cache index files (high system load maybe?). Overall, whenever a system behaves this way the user probably has other problems to solve.
  * If "kill timeout" value is set too low we might incur in the same problem originally reported and end up calling SIGKILL on squid too early, probably while it is closing its cache index files, thus corrupting them. Anyway, this was probably happening already anyway, as SIGKILL is always called after 5 seconds in the current upstart script.

  Overall, there is very low regression potential for this fix.

  
  [Other info]

  # lsb_release -d
  Description:    Ubuntu 12.04.5 LTS
  # dpkg -l squid3
  Desired=Unknown/Install/Remove/Purge/Hold
  | Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
  |/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
  ||/ Name               Version            Description
  +++-==================-==================-====================================================
  ii  squid3             3.1.19-1ubuntu3.12 Full featured Web Proxy cache (HTTP proxy)

  # lsb_release -d
  Description:	Ubuntu 14.04.3 LTS
  # dpkg -l squid3
  Desired=Unknown/Install/Remove/Purge/Hold
  | Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
  |/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
  ||/ Name                                        Version                    Architecture               Description
  +++-===========================================-==========================-==========================-===========================================================================================
  ii  squid3                                      3.3.8-1ubuntu6.3           amd64                      Full featured Web Proxy cache (HTTP proxy)

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