lkml.org 
[lkml]   [2009]   [Oct]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: Process id recycling and status of tasks
From
On Fri, Oct 23, 2009 at 1:43 PM, Clemens Ladisch <clemens@ladisch.de> wrote:
> Leonidas . wrote:
>> 1. What would be an ideal way to check if a task is alive or dead from
>> kernel space?
>
> Get a reference to the task's pid (call get_task_pid(), or get_pid() on
> the return value of task_pid()), then later check whether pid_task()
> works.
>
> (pid_alive() is not what you want because this would require that you
> hold a reference to the task_struct.)
>
>> even though a certain pid might exist, it might have got recycled by
>> the time I check again, right?
>
> The functions above do not work with PID numbers but with struct pid
> which is a reference-counted object.  (The functions with "get" in their
> name increase the reference count, so don't forget to put_pid() when you
> no longer need it.)  See also the big comment in include/linux/pid.h.
>
>
> HTH
> Clemens
>


Yes, the comment in pid.h says it.

Was going through pid.c, what is the fundamental difference between pid_task()
and get_pid_task()? Is it correct to say that, get_pid_task() will
check whether the
task struct is stale or not and return accordingly and pid_task() will
blindly return
task_struct which might be stale?

Now my understanding is get_pid_task() should be followed by put_pid_task()
so the reference counting work as expected, but put_pid_task() is not an
exported symbol? Am I missing here something?

The obvious question which follows from above is what would be the correct
way to determine whether a process is alive or not using pid_alive()? Using
pid_task() does not seem correct and seemingly correct way looks unfeasible.


-Leo.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2009-10-24 20:09    [W:0.060 / U:0.120 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site