From: Pavel Machek <pavel@ucw.cz>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Daniel Colascione <dancol@google.com>,
linux-kernel@vger.kernel.org, rppt@linux.ibm.com,
timmurray@google.com, joelaf@google.com, surenb@google.com,
Jonathan Corbet <corbet@lwn.net>,
Andrew Morton <akpm@linux-foundation.org>,
Roman Gushchin <guro@fb.com>,
Mike Rapoport <rppt@linux.vnet.ibm.com>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
"Dennis Zhou (Facebook)" <dennisszhou@gmail.com>,
Prashant Dhamdhere <pdhamdhe@redhat.com>,
"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>
Subject: Re: [PATCH v2] Document /proc/pid PID reuse behavior
Date: Tue, 20 Nov 2018 10:18:29 +0100 [thread overview]
Message-ID: <20181120091829.GD16916@amd> (raw)
In-Reply-To: <1c5caa66-3c61-cb57-754a-f099200c73b2@suse.cz>
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On Tue 2018-11-20 10:05:21, Vlastimil Babka wrote:
> On 11/19/18 11:54 AM, Pavel Machek wrote:
> > On Mon 2018-11-05 13:22:05, Daniel Colascione wrote:
> >> State explicitly that holding a /proc/pid file descriptor open does
> >> not reserve the PID. Also note that in the event of PID reuse, these
> >> open file descriptors refer to the old, now-dead process, and not the
> >> new one that happens to be named the same numeric PID.
> >>
> >> Signed-off-by: Daniel Colascione <dancol@google.com>
> >> ---
> >> Documentation/filesystems/proc.txt | 7 +++++++
> >> 1 file changed, 7 insertions(+)
> >>
> >> Moved paragraphed to start of /proc/pid section; added signed-off-by.
> >>
> >> 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
> >> +contained files or subdirectories does not prevent <pid> being reused
> >> +for some other process in the event that <pid> exits. Operations on
> >
> > "does not" -> "may not"?
> >
> > We want to leave this unspecified, so that we can change it in future.
>
> Why can't the documentation describe the current implementation, and
> change in the future if the implementation changes? I doubt somebody
Documentation should describe "contract" between kernel and userspace.
> would ever rely on the pid being reused while having the descriptor
> open. How would that make sense?
I agree this is corner space, but users might be surprised that
keeping FDs of /proc/pid/X would lead to PID space exhaustion, for
example.
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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next prev parent reply other threads:[~2018-11-20 9:18 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-31 15:06 [PATCH] Document /proc/pid PID reuse behavior Daniel Colascione
2018-11-01 7:08 ` Mike Rapoport
2018-11-05 13:22 ` [PATCH v2] " Daniel Colascione
2018-11-06 6:01 ` Mike Rapoport
2018-11-07 17:16 ` Matthew Wilcox
2018-11-07 18:21 ` Daniel Colascione
2018-11-06 13:05 ` Michal Hocko
2018-11-07 15:48 ` Daniel Colascione
2018-11-07 16:00 ` Michal Hocko
2018-11-07 16:10 ` Daniel Colascione
2018-11-07 16:19 ` Michal Hocko
2018-11-19 11:16 ` Aleksa Sarai
2018-11-07 17:04 ` Martin Steigerwald
2018-11-08 12:02 ` David Laight
2018-11-08 12:27 ` Matthew Wilcox
2018-11-08 13:42 ` David Laight
2018-11-08 14:07 ` Matthew Wilcox
2018-11-08 14:14 ` David Laight
2018-11-08 13:25 ` Michal Hocko
2018-11-19 10:54 ` Pavel Machek
2018-11-19 16:24 ` Daniel Colascione
2018-11-20 8:50 ` Pavel Machek
2018-11-20 9:05 ` Vlastimil Babka
2018-11-20 9:18 ` Pavel Machek [this message]
2018-11-20 17:39 ` Matthew Wilcox
2018-11-20 17:48 ` Daniel Colascione
2018-11-20 17:59 ` Matthew Wilcox
2018-11-20 16:37 ` Joel Fernandes
2018-11-20 16:49 ` Jonathan Corbet
2018-11-20 16:57 ` Pavel Machek
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