From: Daniel Colascione <dancol@google.com>
To: linux-kernel@vger.kernel.org
Cc: timmurray@google.com, joelaf@google.com, surenb@google.com,
Daniel Colascione <dancol@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>,
Vlastimil Babka <vbabka@suse.cz>,
"Dennis Zhou (Facebook)" <dennisszhou@gmail.com>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Prashant Dhamdhere <pdhamdhe@redhat.com>,
"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>
Subject: [PATCH] Document /proc/pid PID reuse behavior
Date: Wed, 31 Oct 2018 15:06:22 +0000 [thread overview]
Message-ID: <20181031150625.147369-1-dancol@google.com> (raw)
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.
---
Documentation/filesystems/proc.txt | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index 12a5e6e693b6..567f66a8a23c 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -214,6 +214,14 @@ asynchronous manner and the value may not be very precise. To see a precise
snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table.
It's slow but very precise.
+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
+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.
+
Table 1-2: Contents of the status files (as of 4.8)
..............................................................................
Field Content
--
2.19.1.568.g152ad8e336-goog
next reply other threads:[~2018-10-31 15:06 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-31 15:06 Daniel Colascione [this message]
2018-11-01 7:08 ` [PATCH] Document /proc/pid PID reuse behavior 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
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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