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

Daniel Colascione
2018-11-07T18:22:04Z

On Wed, Nov 7, 2018 at 9:16 AM, Matthew Wilcox <willy@infradead.org> wrote:
> 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)

Thanks for spotting that. I had to re-read that sentence three times
or so before even seeing that extra "a".

>> > +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>.

I'll send a new patch version --- unless we can just tweak the patch
when we merge it into the tree?