Commit 38fd525a authored by Eric W. Biederman's avatar Eric W. Biederman
Browse files

exit: Factor thread_group_exited out of pidfd_poll 

Create an independent helper thread_group_exited which returns true
when all threads have passed exit_notify in do_exit.  AKA all of the
threads are at least zombies and might be dead or completely gone.

Create this helper by taking the logic out of pidfd_poll where it is
already tested, and adding a READ_ONCE on the read of
task->exit_state.

I will be changing the user mode driver code to use this same logic
to know when a user mode driver needs to be restarted.

Place the new helper thread_group_exited in kernel/exit.c and
EXPORT it so it can be used by modules.

Link: https://lkml.kernel.org/r/20200702164140.4468-13-ebiederm@xmission.com


Acked-by: default avatarChristian Brauner <christian.brauner@ubuntu.com>
Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
Tested-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
parent 1c340ead

include/linux/sched/signal.h

+2 −0
Original line number Diff line number Diff line
@@ -674,6 +674,8 @@ static inline int thread_group_empty(struct task_struct *p) 
#define delay_group_leader(p) \

		(thread_group_leader(p) && !thread_group_empty(p))



extern bool thread_group_exited(struct pid *pid);



extern struct sighand_struct *__lock_task_sighand(struct task_struct *task,

							unsigned long *flags);

kernel/exit.c

+24 −0
Original line number Diff line number Diff line
@@ -1713,6 +1713,30 @@ Efault: 
}

#endif



/**

 * thread_group_exited - check that a thread group has exited

 * @pid: tgid of thread group to be checked.

 *

 * Test if the thread group represented by tgid has exited (all

 * threads are zombies, dead or completely gone).

 *

 * Return: true if the thread group has exited. false otherwise.

 */

bool thread_group_exited(struct pid *pid)

{

	struct task_struct *task;

	bool exited;



	rcu_read_lock();

	task = pid_task(pid, PIDTYPE_PID);

	exited = !task ||

		(READ_ONCE(task->exit_state) && thread_group_empty(task));

	rcu_read_unlock();



	return exited;

}

EXPORT_SYMBOL(thread_group_exited);



__weak void abort(void)

{

	BUG();

kernel/fork.c

+1 −5
Original line number Diff line number Diff line
@@ -1787,22 +1787,18 @@ static void pidfd_show_fdinfo(struct seq_file *m, struct file *f) 
 */

static __poll_t pidfd_poll(struct file *file, struct poll_table_struct *pts)

{

	struct task_struct *task;

	struct pid *pid = file->private_data;

	__poll_t poll_flags = 0;



	poll_wait(file, &pid->wait_pidfd, pts);



	rcu_read_lock();

	task = pid_task(pid, PIDTYPE_PID);

	/*

	 * Inform pollers only when the whole thread group exits.

	 * If the thread group leader exits before all other threads in the

	 * group, then poll(2) should block, similar to the wait(2) family.

	 */

	if (!task || (task->exit_state && thread_group_empty(task)))

	if (thread_group_exited(pid))

		poll_flags = EPOLLIN | EPOLLRDNORM;

	rcu_read_unlock();



	return poll_flags;

}

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