suse man page for utrace_barrier

UTRACE_BARRIER(9)						  utrace core API						 UTRACE_BARRIER(9)

NAME
       utrace_barrier - synchronize with simultaneous tracing callbacks

SYNOPSIS
       int utrace_barrier(struct task_struct * target, struct utrace_engine * engine);

ARGUMENTS
       target
	   thread to affect

       engine
	   engine to affect (can be detached)

DESCRIPTION
       This blocks while target might be in the midst of making a callback to engine. It can be interrupted by signals and will return
       -ERESTARTSYS. A return value of zero means no callback from target to engine was in progress. Any effect of its return value (such as
       UTRACE_STOP) has already been applied to engine.

       It's not necessary to keep the target pointer alive for this call. It's only necessary to hold a ref on engine. This will return safely
       even if target has been reaped and has no task refs.

       A successful return from utrace_barrier guarantees its ordering with respect to utrace_set_events and utrace_control calls. If target was
       not properly stopped, event callbacks just disabled might still be in progress; utrace_barrier waits until there is no chance an unwanted
       callback can be in progress.

Kernel Hackers Manual 2.6.					     July 2010							 UTRACE_BARRIER(9)