[PATCH] pids: kill PIDTYPE_TGID

This patch kills PIDTYPE_TGID pid_type thus saving one hash table in
kernel/pid.c and speeding up subthreads create/destroy a bit.  It is also a
preparation for the further tref/pids rework.

This patch adds 'struct list_head thread_group' to 'struct task_struct'
instead.

We don't detach group leader from PIDTYPE_PID namespace until another
thread inherits it's ->pid == ->tgid, so we are safe wrt premature
free_pidmap(->tgid) call.

Currently there are no users of find_task_by_pid_type(PIDTYPE_TGID).
Should the need arise, we can use find_task_by_pid()->group_leader.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-By: Eric Biederman <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 3 insertions, 1 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
index 12cdd9fc9d02..bc551efb5fd4 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1112,6 +1112,7 @@ static task_t *copy_process(unsigned long clone_flags,
          * We dont wake it up yet.
          */
         p->group_leader = p;
+        INIT_LIST_HEAD(&p->thread_group);
         INIT_LIST_HEAD(&p->ptrace_children);
         INIT_LIST_HEAD(&p->ptrace_list);
 
@@ -1165,7 +1166,9 @@ static task_t *copy_process(unsigned long clone_flags,
                         retval = -EAGAIN;
                         goto bad_fork_cleanup_namespace;
                 }
+
                 p->group_leader = current->group_leader;
+                list_add_tail_rcu(&p->thread_group, &p->group_leader->thread_group);
 
                 if (current->signal->group_stop_count > 0) {
                         /*
@@ -1213,7 +1216,6 @@ static task_t *copy_process(unsigned long clone_flags,
                         list_add_tail(&p->tasks, &init_task.tasks);
                         __get_cpu_var(process_counts)++;
                 }
-                attach_pid(p, PIDTYPE_TGID, p->tgid);
                 attach_pid(p, PIDTYPE_PID, p->pid);
                 nr_threads++;
         }