Re: [PATCH v2] Document /proc/pid PID reuse behavior

Matthew Wilcox
2018-11-07T17:16:47Z

On Tue, Nov 06, 2018 at 08:01:13AM +0200, Mike Rapoport wrote:
> > diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
> > index 12a5e6e693b6..0b14460f721d 100644
> > --- a/Documentation/filesystems/proc.txt
> > +++ b/Documentation/filesystems/proc.txt
> > @@ -125,6 +125,13 @@ process running on the system, which is named after the process ID (PID).
> > The link self points to the process reading the file system. Each process
> > subdirectory has the entries listed in Table 1-1.
> >
> > +Note that an open a file descriptor to /proc/<pid> or to any of its

"open file descriptor" (the "a" is unnecessary)

> > +contained files or subdirectories does not prevent <pid> being reused
> > +for some other process in the event that <pid> exits. Operations on
> > +open /proc/<pid> file descriptors corresponding to dead processes
> > +never act on any new process that the kernel may, through chance, have
> > +also assigned the process ID <pid>. Instead, operations on these FDs
> > +usually fail with ESRCH.

The paragraph is a bit wordy. More pithy:

An open file descriptor for /proc/<pid> (or any of the files or
subdirectories in it) does not prevent <pid> from being reused after
the process exits. Operations on a file descriptor referring to a dead
process usually return ESRCH. They do not act on any new process which
has been assigned the same <pid>.