[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>

diff --git a/include/linux/pid.h b/include/linux/pid.h
index 099e70e..5b9082c 100644 (file)
--- 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 a913fca..99855f6 100644 (file)
--- 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 aea23e7..22399ca 100644 (file)
--- 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 12cdd9f..bc551ef 100644 (file)
--- 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++;
        }