ptrace: optimize exit_ptrace() for the likely case
exit_ptrace() takes tasklist_lock unconditionally. We need this lock to
avoid the race with ptrace_traceme(), it acts as a barrier.
Change its caller, forget_original_parent(), to call exit_ptrace() under
tasklist_lock. Change exit_ptrace() to drop and reacquire this lock if
This allows us to add the fastpath list_empty(ptraced) check. In the
likely no-tracees case exit_ptrace() just returns and we avoid the lock()
+ unlock() sequence.
"Zhang, Yanmin" <email@example.com> suggested to add this
check, and he reports that this change adds about 11% improvement in some
Suggested-and-tested-by: "Zhang, Yanmin" <firstname.lastname@example.org>
Signed-off-by: Oleg Nesterov <email@example.com>
Acked-by: Roland McGrath <firstname.lastname@example.org>
Signed-off-by: Andrew Morton <email@example.com>
Signed-off-by: Linus Torvalds <firstname.lastname@example.org>