Re: [PATCH 1/3] pidfd_poll: report POLLHUP when pid_task() == NULL

[Christian Brauner <brauner@kernel.org>]

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> TODO: change do_notify_pidfd() to use the keyed wakeups.

How does the following appended patch look?

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From d8ef35f3f151a758cb2503a51dfaf7263480cfbd Mon Sep 17 00:00:00 2001
From: Christian Brauner <brauner@kernel.org>
Date: Fri, 2 Feb 2024 15:18:16 +0100
Subject: [PATCH] pidfd: convert to wake_up_poll()

* Rename do_notify_pidfd() pidfd_wake_up_poll()
* Pass in a poll mask to enable epoll to avoid spurious wakeups
* Use poll_table typedef
* Warn if caller doesn't pass in appropriate poll mask

Suggested-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
---
 include/linux/pid.h |  2 +-
 kernel/exit.c       |  2 +-
 kernel/fork.c       |  4 ++--
 kernel/signal.c     | 10 ++++------
 4 files changed, 8 insertions(+), 10 deletions(-)

diff --git a/include/linux/pid.h b/include/linux/pid.h
index 8124d57752b9..a3666b2ae877 100644
--- a/include/linux/pid.h
+++ b/include/linux/pid.h
@@ -74,7 +74,7 @@ struct pid *pidfd_pid(const struct file *file);
 struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags);
 struct task_struct *pidfd_get_task(int pidfd, unsigned int *flags);
 int pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret);
-void do_notify_pidfd(struct task_struct *task);
+void pidfd_wake_up_poll(struct task_struct *task, __poll_t mask);
 
 static inline struct pid *get_pid(struct pid *pid)
 {
diff --git a/kernel/exit.c b/kernel/exit.c
index c038d10dfb38..b4b39709b046 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -744,7 +744,7 @@ static void exit_notify(struct task_struct *tsk, int group_dead)
 	 * PIDFD_THREAD waiters.
 	 */
 	if (!thread_group_empty(tsk))
-		do_notify_pidfd(tsk);
+		pidfd_wake_up_poll(tsk, EPOLLIN | EPOLLRDNORM | EPOLLHUP);
 
 	if (unlikely(tsk->ptrace)) {
 		int sig = thread_group_leader(tsk) &&
diff --git a/kernel/fork.c b/kernel/fork.c
index aa08193d124f..7b882e66448b 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2074,14 +2074,14 @@ static void pidfd_show_fdinfo(struct seq_file *m, struct file *f)
 /*
  * Poll support for process exit notification.
  */
-static __poll_t pidfd_poll(struct file *file, struct poll_table_struct *pts)
+static __poll_t pidfd_poll(struct file *file, poll_table *wait)
 {
 	struct pid *pid = file->private_data;
 	bool thread = file->f_flags & PIDFD_THREAD;
 	struct task_struct *task;
 	__poll_t poll_flags = 0;
 
-	poll_wait(file, &pid->wait_pidfd, pts);
+	poll_wait(file, &pid->wait_pidfd, wait);
 	/*
 	 * Depending on PIDFD_THREAD, inform pollers when the thread
 	 * or the whole thread-group exits.
diff --git a/kernel/signal.c b/kernel/signal.c
index 9b40109f0c56..ef330a7f1b51 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2019,13 +2019,11 @@ int send_sigqueue(struct sigqueue *q, struct pid *pid, enum pid_type type)
 	return ret;
 }
 
-void do_notify_pidfd(struct task_struct *task)
+void pidfd_wake_up_poll(struct task_struct *task, __poll_t mask)
 {
-	struct pid *pid;
-
 	WARN_ON(task->exit_state == 0);
-	pid = task_pid(task);
-	wake_up_all(&pid->wait_pidfd);
+	WARN_ON(mask == 0);
+	wake_up_poll(&task_pid(task)->wait_pidfd, mask);
 }
 
 /*
@@ -2055,7 +2053,7 @@ bool do_notify_parent(struct task_struct *tsk, int sig)
 	 * non-PIDFD_THREAD waiters.
 	 */
 	if (thread_group_empty(tsk))
-		do_notify_pidfd(tsk);
+		pidfd_wake_up_poll(tsk, EPOLLIN | EPOLLRDNORM);
 
 	if (sig != SIGCHLD) {
 		/*
-- 
2.43.0