Commit [c7e49c]  Maximize  Restore  History

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" <> suggested to add this
check, and he reports that this change adds about 11% improvement in some

Suggested-and-tested-by: "Zhang, Yanmin" <>
Signed-off-by: Oleg Nesterov <>
Acked-by: Roland McGrath <>
Signed-off-by: Andrew Morton <>
Signed-off-by: Linus Torvalds <>

Oleg Nesterov Oleg Nesterov 2010-08-11

Linus Torvalds Linus Torvalds 2010-08-11

changed kernel
changed kernel/exit.c
changed kernel/ptrace.c
kernel/exit.c Diff Switch to side-by-side view
kernel/ptrace.c Diff Switch to side-by-side view