pids: Move the pgrp and session pid pointers from task_struct to signal_struct
To access these fields the code always has to go to group leader so
going to signal struct is no loss and is actually a fundamental simplification.
This saves a little bit of memory by only allocating the pid pointer array
once instead of once for every thread, and even better this removes a
few potential races caused by the fact that group_leader can be changed
by de_thread, while signal_struct can not.
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
diff --git a/kernel/pid.c b/kernel/pid.c
index d0de2b5..f8486d2 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -265,27 +265,35 @@ struct pid *find_vpid(int nr)
}
EXPORT_SYMBOL_GPL(find_vpid);
+static struct pid **task_pid_ptr(struct task_struct *task, enum pid_type type)
+{
+ return (type == PIDTYPE_PID) ?
+ &task->thread_pid :
+ (type == __PIDTYPE_TGID) ?
+ &task->signal->leader_pid :
+ &task->signal->pids[type];
+}
+
/*
* attach_pid() must be called with the tasklist_lock write-held.
*/
void attach_pid(struct task_struct *task, enum pid_type type)
{
- struct pid_link *link = &task->pids[type];
- hlist_add_head_rcu(&link->node, &link->pid->tasks[type]);
+ struct pid *pid = *task_pid_ptr(task, type);
+ hlist_add_head_rcu(&task->pid_links[type], &pid->tasks[type]);
}
static void __change_pid(struct task_struct *task, enum pid_type type,
struct pid *new)
{
- struct pid_link *link;
+ struct pid **pid_ptr = task_pid_ptr(task, type);
struct pid *pid;
int tmp;
- link = &task->pids[type];
- pid = link->pid;
+ pid = *pid_ptr;
- hlist_del_rcu(&link->node);
- link->pid = new;
+ hlist_del_rcu(&task->pid_links[type]);
+ *pid_ptr = new;
for (tmp = PIDTYPE_MAX; --tmp >= 0; )
if (!hlist_empty(&pid->tasks[tmp]))
@@ -310,8 +318,9 @@ void change_pid(struct task_struct *task, enum pid_type type,
void transfer_pid(struct task_struct *old, struct task_struct *new,
enum pid_type type)
{
- new->pids[type].pid = old->pids[type].pid;
- hlist_replace_rcu(&old->pids[type].node, &new->pids[type].node);
+ if (type == PIDTYPE_PID)
+ new->thread_pid = old->thread_pid;
+ hlist_replace_rcu(&old->pid_links[type], &new->pid_links[type]);
}
struct task_struct *pid_task(struct pid *pid, enum pid_type type)
@@ -322,7 +331,7 @@ struct task_struct *pid_task(struct pid *pid, enum pid_type type)
first = rcu_dereference_check(hlist_first_rcu(&pid->tasks[type]),
lockdep_tasklist_lock_is_held());
if (first)
- result = hlist_entry(first, struct task_struct, pids[(type)].node);
+ result = hlist_entry(first, struct task_struct, pid_links[(type)]);
}
return result;
}
@@ -360,9 +369,7 @@ struct pid *get_task_pid(struct task_struct *task, enum pid_type type)
{
struct pid *pid;
rcu_read_lock();
- if (type != PIDTYPE_PID)
- task = task->group_leader;
- pid = get_pid(rcu_dereference(task->pids[type].pid));
+ pid = get_pid(rcu_dereference(*task_pid_ptr(task, type)));
rcu_read_unlock();
return pid;
}
@@ -420,16 +427,8 @@ pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type,
rcu_read_lock();
if (!ns)
ns = task_active_pid_ns(current);
- if (likely(pid_alive(task))) {
- struct pid *pid;
- if (type == PIDTYPE_PID)
- pid = task_pid(task);
- else if (type == __PIDTYPE_TGID)
- pid = task_tgid(task);
- else
- pid = rcu_dereference(task->group_leader->pids[type].pid);
- nr = pid_nr_ns(pid, ns);
- }
+ if (likely(pid_alive(task)))
+ nr = pid_nr_ns(rcu_dereference(*task_pid_ptr(task, type)), ns);
rcu_read_unlock();
return nr;
