D5547: Prevent kcheckpass from becoming an orphan

[Martin Gräßlin]

graesslin created this revision.
Restricted Application added a project: Plasma.
Restricted Application added a subscriber: plasma-devel.

REVISION SUMMARY
  With the long running kcheckpass there is the possibility that
  kcheckpass becomes an orphan. Kcheckpass terminates once it gets
  SIGUSR2 sent from the parent process (that is kscreenlocker_greet).
  
  If kscreenlocker_greet crashes it cannot send SIGUSR2 to kcheckpass and
  thus kcheckpass becomes an orphan. This can easily be seen in the
  killTest autotest which results in many orphaned kcheckpass processes
  after execution.
  
  This change uses the linux specific PR_SET_PDEATHSIG to send SIGUSR2 to
  kcheckpass when the parent process dies. Thus kcheckpass can get out of
  the waiting and terminate without becoming an orphan.
  
  In this case it is not a problem to use a linux specific syscall. The
  long running kcheckpass is only used if kscreenlocker is built with
  seccomp support which is also linux specific.

TEST PLAN
  Run killTest and check the number of orphaned kcheckpass.
  Without this change we had 17 orphaned processes, with this change none.

REPOSITORY
  R133 KScreenLocker

BRANCH
  kcheckpass-no-orphan

REVISION DETAIL
  https://phabricator.kde.org/D5547

AFFECTED FILES
  kcheckpass/kcheckpass.c

To: graesslin, #plasma
Cc: plasma-devel, spstarr, progwolff, lesliezhai, ali-mohamed, jensreuterberg, abetts, sebas, apol
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