[PATCH] pid: Implement transfer_pid and use it to simplify de_thread
In de_thread we move pids from one process to another, a rather ugly case.
The function transfer_pid makes it clear what we are doing, and makes the
action atomic. This is useful we ever want to atomically traverse the
process group and session lists, in a rcu safe manner.
Even if the atomic properties this change should be a win as transfer_pid
should be less code to execute than executing both attach_pid and
detach_pid, and this should make de_thread slightly smaller as only a
single function call needs to be emitted. The only downside is that the
code might be slower to execute as the odds are against transfer_pid being
in cache.
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/fs/exec.c b/fs/exec.c
index 54135df..b7aa3d6 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -696,23 +696,20 @@
*/
/* Become a process group leader with the old leader's pid.
- * Note: The old leader also uses thispid until release_task
+ * The old leader becomes a thread of the this thread group.
+ * Note: The old leader also uses this pid until release_task
* is called. Odd but simple and correct.
*/
detach_pid(current, PIDTYPE_PID);
current->pid = leader->pid;
attach_pid(current, PIDTYPE_PID, current->pid);
- attach_pid(current, PIDTYPE_PGID, current->signal->pgrp);
- attach_pid(current, PIDTYPE_SID, current->signal->session);
+ transfer_pid(leader, current, PIDTYPE_PGID);
+ transfer_pid(leader, current, PIDTYPE_SID);
list_replace_rcu(&leader->tasks, ¤t->tasks);
current->group_leader = current;
leader->group_leader = current;
- /* Reduce leader to a thread */
- detach_pid(leader, PIDTYPE_PGID);
- detach_pid(leader, PIDTYPE_SID);
-
current->exit_signal = SIGCHLD;
BUG_ON(leader->exit_state != EXIT_ZOMBIE);