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[PATCH] pid: Implement transfer_pid and use it to simplify de_thread

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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>
This commit is contained in:
Eric W. Biederman
2006-09-27 01:51:06 -07:00
committed by Linus Torvalds
parent 35fa2048ab
commit c18258c6f0
3 changed files with 15 additions and 7 deletions
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11
fs/exec.c
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@ -696,23 +696,20 @@ static int de_thread(struct task_struct *tsk)
*/
/* 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, &current->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);