Re: [PATCH RFC 1/2] Add polling support to pidfd

On 04/11, Joel Fernandes (Google) wrote:

+static unsigned int proc_tgid_base_poll(struct file *file, struct poll_table_struct *pts) +{

• int poll_flags = 0;
• struct task_struct *task;
• struct pid *pid;
• task = get_proc_task(file->f_path.dentry->d_inode);
• WARN_ON_ONCE(task && !thread_group_leader(task));
• /*

• * tasklist_lock must be held because to avoid racing with
  

• * changes in exit_state and wake up. Basically to avoid:
  

• *
  

• * P0: read exit_state = 0
  

• * P1: write exit_state = EXIT_DEAD
  

• * P1: Do a wake up - wq is empty, so do nothing
  

• * P0: Queue for polling - wait forever.
  

• */
  

• read_lock(&tasklist_lock);
• if (!task)

• poll_flags = POLLIN | POLLRDNORM | POLLERR;
  

• else if (task->exit_state == EXIT_DEAD)

• poll_flags = POLLIN | POLLRDNORM;
  

• else if (task->exit_state == EXIT_ZOMBIE && thread_group_empty(task))

• poll_flags = POLLIN | POLLRDNORM;
  

• if (!poll_flags) {

• pid = proc_pid(file->f_path.dentry->d_inode);
  

• poll_wait(file, &pid->wait_pidfd, pts);
  

• }

can't understand...

Could you explain when it should return POLLIN? When the whole process exits?

Then all you need is

!task || task->exit_state && thread_group_empty(task)

Please do not use EXIT_DEAD/EXIT_ZOMBIE. And ->wait_pidfd should probably live in task->signal_struct.

Oleg.