Unverified Commit 0b7747a5 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Christian Brauner
Browse files

pidfs: cleanup the usage of do_notify_pidfd() 



If a single-threaded process exits do_notify_pidfd() will be called twice,
from exit_notify() and right after that from do_notify_parent().

1. Change exit_notify() to call do_notify_pidfd() if the exiting task is
   not ptraced and it is not a group leader.

2. Change do_notify_parent() to call do_notify_pidfd() unconditionally.

   If tsk is not ptraced, do_notify_parent() will only be called when it
   is a group-leader and thread_group_empty() is true.

This means that if tsk is ptraced, do_notify_pidfd() will be called from
do_notify_parent() even if tsk is a delay_group_leader(). But this case is
less common, and apart from the unnecessary __wake_up() is harmless.

Granted, this unnecessary __wake_up() can be avoided, but I don't want to
do it in this patch because it's just a consequence of another historical
oddity: we notify the tracer even if !thread_group_empty(), but do_wait()
from debugger can't work until all other threads exit. With or without this
patch we should either eliminate do_notify_parent() in this case, or change
do_wait(WEXITED) to untrace the ptraced delay_group_leader() at least when
ptrace_reparented().

Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Link: https://lore.kernel.org/r/20250323171955.GA834@redhat.com


Signed-off-by: default avatarChristian Brauner <brauner@kernel.org>
parent 2df0c02d

kernel/exit.c

+2 −6
Original line number Diff line number Diff line
@@ -756,12 +756,6 @@ static void exit_notify(struct task_struct *tsk, int group_dead) 
		kill_orphaned_pgrp(tsk->group_leader, NULL);



	tsk->exit_state = EXIT_ZOMBIE;

	/*

	 * Ignore thread-group leaders that exited before all

	 * subthreads did.

	 */

	if (!delay_group_leader(tsk))

		do_notify_pidfd(tsk);



	if (unlikely(tsk->ptrace)) {

		int sig = thread_group_leader(tsk) &&
@@ -774,6 +768,8 @@ static void exit_notify(struct task_struct *tsk, int group_dead) 
			do_notify_parent(tsk, tsk->exit_signal);

	} else {

		autoreap = true;

		/* untraced sub-thread */

		do_notify_pidfd(tsk);

	}



	if (autoreap) {

kernel/signal.c

+3 −5
Original line number Diff line number Diff line
@@ -2179,10 +2179,8 @@ bool do_notify_parent(struct task_struct *tsk, int sig) 


	WARN_ON_ONCE(!tsk->ptrace &&

	       (tsk->group_leader != tsk || !thread_group_empty(tsk)));

	/*

	 * Notify for thread-group leaders without subthreads.

	 */

	if (thread_group_empty(tsk))



	/* ptraced, or group-leader without sub-threads */

	do_notify_pidfd(tsk);



	if (sig != SIGCHLD) {