centos man page for threadgroup_lock

THREADGROUP_LOCK(9)						   Driver Basics					       THREADGROUP_LOCK(9)

NAME
       threadgroup_lock - lock threadgroup

SYNOPSIS
       void threadgroup_lock(struct task_struct * tsk);

ARGUMENTS
       tsk
	   member task of the threadgroup to lock

DESCRIPTION
       Lock the threadgroup tsk belongs to. No new task is allowed to enter and member tasks aren't allowed to exit (as indicated by PF_EXITING)
       or change ->group_leader/pid. This is useful for cases where the threadgroup needs to stay stable across blockable operations.

       fork and exit paths explicitly call threadgroup_change_{begin|end}() for synchronization. While held, no new task will be added to
       threadgroup and no existing live task will have its PF_EXITING set.

       de_thread does threadgroup_change_{begin|end}() when a non-leader sub-thread becomes a new leader.

COPYRIGHT
Kernel Hackers Manual 3.10					     June 2014						       THREADGROUP_LOCK(9)