linux-kernel - Re: Process id recycling and status of tasks

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Date:	Mon, 26 Oct 2009 09:41:45 +0100
From:	Clemens Ladisch <clemens@...isch.de>
To:	"Leonidas ." <leonidas137@...il.com>
CC:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Process id recycling and status of tasks

Leonidas . wrote:
> On Fri, Oct 23, 2009 at 1:43 PM, Clemens Ladisch <clemens@...isch.de> wrote:
> > Get a reference to the task's pid (...), then later check whether
> > pid_task() works.
> 
> Was going through pid.c, what is the fundamental difference between pid_task()
> and get_pid_task()?

As I said, the functions with "get" in their name increase the reference
count.  In other words, get_pid_task(p) is implemented as
get_task(pid_task(p)), so, if it succeeded, you would then own a
reference to the task.

> 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?

You'd have a standard task_struct, so you'd just use put_task().  And if
you don't actually want a reference to the task (because you only want
to check whether the task still exists), just use pid_task() instead.

HTH
Clemens
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