Thomas Gleixner wrote: > > send_sigqueue is called from posix_timer_fn() and acquires > tasklist_lock, which makes no sense to me. > > send_sigqueue()s (l)onl(e)y user is the posix_timer function > (posix_timer_fn(), calling posix_timer_event()). > > Each posix timer blocks the task from vanishing away by > get_task_struct(), which is protected by the held tasklist_lock. > > The task can neither go away nor the signal handler can change until > put_task_struct() is called inside release_posix_timer(), which removes > any chance to do an invalid access to either task or sighand because the > relevant timer is deleted before the call to put_task_struct(). Also > this call is protected by tasklist_lock().
Yes, the task_struct can't go away, but if process exited this task_struct is just chunk of garbage. I think the intent was to protect against this case. However, I agree with you, locking the tasklist_lock can't help, and the code is wrong. posix_timer_event() first checks that the thread (SIGEV_THREAD_ID case) does not have PF_EXITING flag, then it calls send_sigqueue() which locks task list. But if the thread exits in between the kernel will oops. posix_timer_event() runs under k_itimer.it_lock, but this does not help if that thread was not the only one in thread group, in this case we don't call exit_itimers(). The comment is wrong too. ->sighand can't change, we are clearing posix timer on exec, and tasklist can't prevent ->sighand from going away.. Ingo, Roland, George, am I wrong? Oleg. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
