Messages in this thread | | | Date | Wed, 18 Jan 2023 12:06:49 +0100 | From | Petr Mladek <> | Subject | Re: [PATCH] sched: print parent comm in sched_show_task() |
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On Tue 2023-01-17 08:33:56, 张元瀚 Tio Zhang wrote: > Hi Chen, > Thanks for your reply! I implement this according to Petr's suggestion here: > > > A solution would be to move the parent value to another line. > > It would even better solve the situation when the task > > is not alive and we could not get information about the parent: > > > > if (pid_alive(p)) { > > struct parent = rcu_dereference(p->real_parent); > > > > pr_info("parent:%-15.15s ppid:%-6d\n", > > parent->comm, task_pid_nr(parent)); > > } > > It seems do break the original format, but I guess printing 0 as ppid when the task is not alive > would also confuse people sometimes.
Well, a task with pid 0 does not exist so it is not that bad. But I agree that we could do better.
> For example, when people (and also most system monitor software) see ppid, they read the value in /proc/PID/status. According to task_tgid_nr_ns(), when the task is in a container with its parent outside the > namespace, we will also see that ppid is 0 inside the container. And in our sched_show_task() here, we are calling task_pid_nr(), so the inconsistency maybe would confuse people under this scenario. > > So maybe this new line style would be a better choice? Or we just keep the original format and > move the parent's info (and should we print the parent's pid again here) to a new line.
What about printing something like:
pr_info("parent:unknown\n");
or
pr_info("parent:unknown ppid:<NULL>;
or
pr_info("parent:???\n");
or
pr_info("parent:unknown (task is exiting)\n");
I slightly prefer the 2nd variant. The <NULL> string makes it rather clear that the information is not accessible. And pid_alive() actually does:
return p->thread_pid != NULL;
Best Regards, Petr
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