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authorEric W. Biederman <ebiederm@xmission.com>2006-09-27 01:51:06 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2006-09-27 08:26:19 -0700
commitc18258c6f0848f97e85287f6271c511a092bb784 (patch)
tree16c057a171b7623895ee208459392c1104193b84
parent35fa2048ab13d1be846be612e395c15c200bd51c (diff)
[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>
-rw-r--r--fs/exec.c11
-rw-r--r--include/linux/pid.h2
-rw-r--r--kernel/pid.c9
3 files changed, 15 insertions, 7 deletions
diff --git a/fs/exec.c b/fs/exec.c
index 54135df2a96..b7aa3d6422d 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -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);
diff --git a/include/linux/pid.h b/include/linux/pid.h
index 29960b03bef..93da7e2d9f3 100644
--- a/include/linux/pid.h
+++ b/include/linux/pid.h
@@ -76,6 +76,8 @@ extern int FASTCALL(attach_pid(struct task_struct *task,
enum pid_type type, int nr));
extern void FASTCALL(detach_pid(struct task_struct *task, enum pid_type));
+extern void FASTCALL(transfer_pid(struct task_struct *old,
+ struct task_struct *new, enum pid_type));
/*
* look up a PID in the hash table. Must be called with the tasklist_lock
diff --git a/kernel/pid.c b/kernel/pid.c
index 93e212f2067..6db82b68e2f 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -252,6 +252,15 @@ void fastcall detach_pid(struct task_struct *task, enum pid_type type)
free_pid(pid);
}
+/* transfer_pid is an optimization of attach_pid(new), detach_pid(old) */
+void fastcall 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);
+ old->pids[type].pid = NULL;
+}
+
struct task_struct * fastcall pid_task(struct pid *pid, enum pid_type type)
{
struct task_struct *result = NULL;