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Message-ID: <CAKOZuet9KGHc9dAyC=-cMZNt39s2m9=YEu3R1-7ExWzaNzLzjA@mail.gmail.com>
Date: Wed, 7 Nov 2018 10:21:59 -0800
From: Daniel Colascione <dancol@...gle.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: Mike Rapoport <rppt@...ux.ibm.com>,
linux-kernel <linux-kernel@...r.kernel.org>,
Tim Murray <timmurray@...gle.com>,
Joel Fernandes <joelaf@...gle.com>,
Suren Baghdasaryan <surenb@...gle.com>,
Jonathan Corbet <corbet@....net>,
Andrew Morton <akpm@...ux-foundation.org>,
Roman Gushchin <guro@...com>, Vlastimil Babka <vbabka@...e.cz>,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
"Dennis Zhou (Facebook)" <dennisszhou@...il.com>,
Prashant Dhamdhere <pdhamdhe@...hat.com>,
"open list:DOCUMENTATION" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH v2] Document /proc/pid PID reuse behavior
On Wed, Nov 7, 2018 at 9:16 AM, Matthew Wilcox <willy@...radead.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?
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