RE: [PATCH] Add /proc/pid_generation

[David Laight <David.Laight@ACULAB.COM>]

From: Kevin Easton
> Sent: 22 November 2018 11:20
> 
> On Wed, Nov 21, 2018 at 12:14:44PM -0800, Daniel Colascione wrote:
> > This change adds a per-pid-namespace 64-bit generation number,
> > incremented on PID rollover, and exposes it via a new proc file
> > /proc/pid_generation. By examining this file before and after /proc
> > enumeration, user code can detect the potential reuse of a PID and
> > restart the task enumeration process, repeating until it gets a
> > coherent snapshot.
> 
> I see downthread this patch has been withdrawn, but nonetheless I'm
> still curious - does this actually solve the problem?
> 
> It seems to me that a PID could be reused within a scan even if the
> generation number remains the same at the beginning and end of a scan:

Why not allocate a 48bit generation number to each 16bit pid?
Then you have a 64bit 'extended-pid' that can be assumed to never be reused.
Provided enough interfaces are enhanced to support 'extended-pid' values
you'll never get reused values.

	David

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