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exit: Factor thread_group_exited out of pidfd_poll

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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: Christian Brauner <christian.brauner@ubuntu.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Tested-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
This commit is contained in:
Eric W. Biederman 2020-07-01 07:30:06 -05:00
parent 1c340ead18
commit 38fd525a4c
3 changed files with 27 additions and 5 deletions
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2
include/linux/sched/signal.h
View File

@ -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);

24
kernel/exit.c
View File

@ -1713,6 +1713,30 @@ COMPAT_SYSCALL_DEFINE5(waitid,
}
#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();

6
kernel/fork.c
View File

@ -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;
}