ptrace: optimize exit_ptrace() for the likely case
authorOleg Nesterov <oleg@redhat.com>
Wed, 11 Aug 2010 01:03:07 +0000 (18:03 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Wed, 11 Aug 2010 15:59:19 +0000 (08:59 -0700)
commitc7e49c1488ab20342eaaf38f1ca35a207f4c051d
tree43876a69cafbb49ce86f71ba5db88018ca7cc036
parent13d7e3a2dba6a79589ed34dc0b9114d7b5ff9eab
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
needed.

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" <yanmin_zhang@linux.intel.com> suggested to add this
check, and he reports that this change adds about 11% improvement in some
tests.

Suggested-and-tested-by: "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
kernel/exit.c
kernel/ptrace.c