lkml.org 
[lkml]   [2020]   [Jul]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Date
Subject[PATCH v3 13/16] exit: Factor thread_group_exited out of pidfd_poll
Create an independent helper thread_group_exited report return 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 missing 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.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
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
+ * 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
\
 
 \ /
  Last update: 2020-07-02 18:49    [W:0.237 / U:2.308 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site