pidfd: change do_notify_pidfd() to use __wake_up(poll_to_key(EPOLLIN))

rather than wake_up_all(). This way do_notify_pidfd() won't wakeup the
POLLHUP-only waiters which wait for pid_task() == NULL.

TODO:
    - as Christian pointed out, this asks for the new wake_up_all_poll()
      helper, it can already have other users.

    - we can probably discriminate the PIDFD_THREAD and non-PIDFD_THREAD
      waiters, but this needs more work. See
      https://lore.kernel.org/all/20240205140848.GA15853@redhat.com/

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Link: https://lore.kernel.org/r/20240205141348.GA16539@redhat.com
Reviewed-by: Tycho Andersen <tandersen@netflix.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/kernel/signal.c b/kernel/signal.c
index 9b40109f0c56482d879947bdb0a194b55538e438..c3fac06937e2800d52fb957e4a263828788aaf2d 100644 (file)
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2021,11 +2021,12 @@ ret:
 
 void do_notify_pidfd(struct task_struct *task)
 {
-       struct pid *pid;
+       struct pid *pid = task_pid(task);
 
        WARN_ON(task->exit_state == 0);
-       pid = task_pid(task);
-       wake_up_all(&pid->wait_pidfd);
+
+       __wake_up(&pid->wait_pidfd, TASK_NORMAL, 0,
+                       poll_to_key(EPOLLIN | EPOLLRDNORM));
 }
 
 /*