kernel/fork.c:copy_process(): don't add the uninitialized child to thread/task/pid lists
copy_process() adds the new child to thread_group/init_task.tasks list and
then does attach_pid(child, PIDTYPE_PID). This means that the lockless
next_thread() or next_task() can see this thread with the wrong pid. Say,
"ls /proc/pid/task" can list the same inode twice.
We could move attach_pid(child, PIDTYPE_PID) up, but in this case
find_task_by_vpid() can find the new thread before it was fully
initialized.
And this is already true for PIDTYPE_PGID/PIDTYPE_SID, With this patch
copy_process() initializes child->pids[*].pid first, then calls
attach_pid() to insert the task into the pid->tasks list.
attach_pid() no longer need the "struct pid*" argument, it is always
called after pid_link->pid was already set.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Sergey Dyasly <dserrg@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/kernel/pid.c b/kernel/pid.c
index 0db3e79..61980ce 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -373,14 +373,10 @@
/*
* attach_pid() must be called with the tasklist_lock write-held.
*/
-void attach_pid(struct task_struct *task, enum pid_type type,
- struct pid *pid)
+void attach_pid(struct task_struct *task, enum pid_type type)
{
- struct pid_link *link;
-
- link = &task->pids[type];
- link->pid = pid;
- hlist_add_head_rcu(&link->node, &pid->tasks[type]);
+ struct pid_link *link = &task->pids[type];
+ hlist_add_head_rcu(&link->node, &link->pid->tasks[type]);
}
static void __change_pid(struct task_struct *task, enum pid_type type,
@@ -412,7 +408,7 @@
struct pid *pid)
{
__change_pid(task, type, pid);
- attach_pid(task, type, pid);
+ attach_pid(task, type);
}
/* transfer_pid is an optimization of attach_pid(new), detach_pid(old) */