On 02/06, Tycho Andersen wrote: > > From: Tycho Andersen <tandersen@xxxxxxxxxxx> > > We can get EBADF from __pidfd_fget() if a task is currently exiting, which > might be confusing. agreed, because EBADF looks as if the "fd" argument was wrong, > Let's check PF_EXITING, and just report ESRCH if so. agreed, we can pretend that the task has already exited, But: > --- a/kernel/pid.c > +++ b/kernel/pid.c > @@ -688,7 +688,7 @@ static int pidfd_getfd(struct pid *pid, int fd) > int ret; > > task = get_pid_task(pid, PIDTYPE_PID); > - if (!task) > + if (!task || task->flags & PF_EXITING) > return -ESRCH; This looks racy. Suppose that pidfd_getfd() races with the exiting task. It is possible that this task sets PF_EXITING and does exit_files() after the "task->flags & PF_EXITING" check above and before pidfd_getfd() does __pidfd_fget(), in this case pidfd_getfd() still returns the same EBADF we want to avoid. Perhaps we can change pidfd_getfd() to do if (IS_ERR(file)) return (task->flags & PF_EXITING) ? -ESRCH : PTR_ERR(file); instead? This needs a comment to explain the PF_EXITING check. And perhaps another comment to explain that we can't miss PF_EXITING if the target task has already passed exit_files, both exit_files() and fget_task() take the same task_lock(task). What do you think? Oleg.
