[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>

2 files changed, 4 insertions, 10 deletions

diff --git a/kernel/exit.c b/kernel/exit.c
index aea23e713cf4..22399caf7574 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -51,7 +51,6 @@ static void __unhash_process(struct task_struct *p)
 {
         nr_threads--;
         detach_pid(p, PIDTYPE_PID);
-        detach_pid(p, PIDTYPE_TGID);
         if (thread_group_leader(p)) {
                 detach_pid(p, PIDTYPE_PGID);
                 detach_pid(p, PIDTYPE_SID);
@@ -59,7 +58,7 @@ static void __unhash_process(struct task_struct *p)
                 list_del_init(&p->tasks);
                 __get_cpu_var(process_counts)--;
         }
-
+        list_del_rcu(&p->thread_group);
         remove_parent(p);
 }
 
@@ -964,13 +963,6 @@ asmlinkage long sys_exit(int error_code)
         do_exit((error_code&0xff)<<8);
 }
 
-task_t fastcall *next_thread(const task_t *p)
-{
-        return pid_task(p->pids[PIDTYPE_TGID].pid_list.next, PIDTYPE_TGID);
-}
-
-EXPORT_SYMBOL(next_thread);
-
 /*
  * Take down every thread in the group.  This is called by fatal signals
  * as well as by sys_exit_group (below).
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++;
         }