On Thu, Jul 02, 2020 at 11:41:37AM -0500, Eric W. Biederman wrote: > Create an independent helper thread_group_exited report return true
s/report return/which reports/ > 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 missing READ_ONCE on > the read of task->exit_state. I would prefer to have this comment dropped as this read_once() is not missing as you can see from the comments elsewhere in this thread. > > 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. > > Signed-off-by: "Eric W. Biederman" <[email protected]> > --- Minus the typos above and below, this looks good and passes the pidfd and process test-suite. Acked-by: Christian Brauner <[email protected]> Thanks! Christian > include/linux/sched/signal.h | 2 ++ > kernel/exit.c | 24 ++++++++++++++++++++++++ > kernel/fork.c | 6 +----- > 3 files changed, 27 insertions(+), 5 deletions(-) > > diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h > index 0ee5e696c5d8..1bad18a1d8ba 100644 > --- a/include/linux/sched/signal.h > +++ b/include/linux/sched/signal.h > @@ -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); > > diff --git a/kernel/exit.c b/kernel/exit.c > index d3294b611df1..a7f112feb0f6 100644 > --- a/kernel/exit.c > +++ b/kernel/exit.c > @@ -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 thread group is has exited (all threads are zombies, dead s/is has exited/has exited/ > + * 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(); > diff --git a/kernel/fork.c b/kernel/fork.c > index 142b23645d82..bf215af7a904 100644 > --- a/kernel/fork.c > +++ b/kernel/fork.c > @@ -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; > } > -- > 2.25.0 >
