On Tue, Oct 15, 2019 at 04:43:57PM +0200, Oleg Nesterov wrote:
On 10/15, Christian Brauner wrote:
+static inline bool task_alive(struct pid *pid) +{
- bool alive = true;
- rcu_read_lock();
- if (!pid_task(pid, PIDTYPE_PID))
alive = false;- rcu_read_unlock();
- return alive;
+}
Well, the usage of rcu_read_lock/unlock looks confusing to me...
I mean, this helper does not need rcu lock at all. Except rcu_dereference_check() will complain.
Yep, I think we have another codepath were the rcu locks might be purely cosmetic so I thought it's not a big deal (see below).
static inline bool task_alive(struct pid *pid) { bool alive;
/* shut up rcu_dereference_check() */ rcu_lock_acquire(&rcu_lock_map); alive = !!pid_task(pid, PIDTYPE_PID)); rcu_lock_release(&rcu_lock_map); return alive;}
looks more clear imo.
But in fact I'd suggest to simply use !hlist_empty(&pid->tasks[PIDTYPE_PID]) in pidfd_show_fdinfo() and do not add a new helper.
Sounds good to me. But can't we then just do something similar just with !hlist_empty(&pid->tasks[PIDTYPE_TGID])
in v5.4-rc3:kernel/pid.c:pidfd_open():514-517 ?
or would this be problematic because of de_thread()?
Thanks! Christian