[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>

4 files changed, 12 insertions, 14 deletions

diff --git a/include/linux/pid.h b/include/linux/pid.h
index 099e70ecf7c7..5b9082cc600f 100644
--- a/include/linux/pid.h
+++ b/include/linux/pid.h
@@ -4,7 +4,6 @@
 enum pid_type
 {
         PIDTYPE_PID,
-        PIDTYPE_TGID,
         PIDTYPE_PGID,
         PIDTYPE_SID,
         PIDTYPE_MAX
diff --git a/include/linux/sched.h b/include/linux/sched.h
index a913fca9e70d..99855f694ebd 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -752,6 +752,7 @@ struct task_struct {
 
         /* PID/PID hash table linkage. */
         struct pid pids[PIDTYPE_MAX];
+        struct list_head thread_group;
 
         struct completion *vfork_done;          /* for vfork() */
         int __user *set_child_tid;              /* CLONE_CHILD_SETTID */
@@ -1192,13 +1193,17 @@ extern void wait_task_inactive(task_t * p);
 #define while_each_thread(g, t) \
         while ((t = next_thread(t)) != g)
 
-extern task_t * FASTCALL(next_thread(const task_t *p));
-
 #define thread_group_leader(p)  (p->pid == p->tgid)
 
+static inline task_t *next_thread(task_t *p)
+{
+        return list_entry(rcu_dereference(p->thread_group.next),
+                                task_t, thread_group);
+}
+
 static inline int thread_group_empty(task_t *p)
 {
-        return list_empty(&p->pids[PIDTYPE_TGID].pid_list);
+        return list_empty(&p->thread_group);
 }
 
 #define delay_group_leader(p) \
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++;
         }