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syscalls: ‘processes’ really omits kernel threads.

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Fixes a bug whereby ‘processes’ would include kernel threads, thereby
leading the ‘stop’ method of ‘user-processes’ to wait indefinitely for a
kernel thread.  Code taken from the Shepherd.

Fixes <https://issues.guix.gnu.org/68800>.

* guix/build/syscalls.scm (kernel?): Remove.
(linux-process-flags, linux-kernel-thread?, pseudo-process?): New
procedures.
(PF_KTHREAD): New variable.
(processes): Use ‘pseudo-process?’ instead of ‘kernel?’.

Reported-by: Tomas Volf <~@wolfsden.cz>
Change-Id: I8c439cdaf868a8f899de7fe500ce8bf10e5fc290
This commit is contained in:
Ludovic Courtès 2024-02-20 10:46:42 +01:00
parent 5d81aa8613
commit 34c79c6ae8
No known key found for this signature in database
GPG key ID: 090B11993D9AEBB5
1 changed files with 39 additions and 16 deletions
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55
guix/build/syscalls.scm
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@ -1,5 +1,5 @@
;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2014-2023 Ludovic Courtès <ludo@gnu.org>
;;; Copyright © 2014-2024 Ludovic Courtès <ludo@gnu.org>
;;; Copyright © 2015 David Thompson <davet@gnu.org>
;;; Copyright © 2015 Mark H Weaver <mhw@netris.org>
;;; Copyright © 2017 Mathieu Othacehe <m.othacehe@gmail.com>
@ -765,27 +765,50 @@ (define-as-needed load-linux-module
(list (strerror err))
(list err)))))))
(define (kernel? pid)
"Return #t if PID designates a \"kernel thread\" rather than a normal
user-land process."
(let ((stat (call-with-input-file (format #f "/proc/~a/stat" pid)
(compose string-tokenize read-string))))
;; See proc.txt in Linux's documentation for the list of fields.
(match stat
((pid tcomm state ppid pgrp sid tty_nr tty_pgrp flags min_flt
cmin_flt maj_flt cmaj_flt utime stime cutime cstime
priority nice num_thread it_real_value start_time
vsize rss rsslim
(= string->number start_code) (= string->number end_code) _ ...)
;; Got this obscure trick from sysvinit's 'killall5' program.
(and (zero? start_code) (zero? end_code))))))
(define (linux-process-flags pid) ;copied from the Shepherd
"Return the process flags of @var{pid} (or'd @code{PF_} constants), assuming
the Linux /proc file system is mounted; raise a @code{system-error} exception
otherwise."
(call-with-input-file (string-append "/proc/" (number->string pid)
"/stat")
(lambda (port)
(define line
(read-string port))
;; Parse like systemd's 'is_kernel_thread' function.
(let ((offset (string-index line #\)))) ;offset past 'tcomm' field
(match (and offset
(string-tokenize (string-drop line (+ offset 1))))
((state ppid pgrp sid tty-nr tty-pgrp flags . _)
(or (string->number flags) 0))
(_
0))))))
;; Per-process flag defined in <linux/sched.h>.
(define PF_KTHREAD #x00200000) ;I am a kernel thread
(define (linux-kernel-thread? pid)
"Return true if @var{pid} is a Linux kernel thread."
(= PF_KTHREAD (logand (linux-process-flags pid) PF_KTHREAD)))
(define pseudo-process?
(if (string-contains %host-type "linux")
(lambda (pid)
"Return true if @var{pid} denotes a \"pseudo-process\" such as a Linux
kernel thread rather than a \"regular\" process. A pseudo-process is one that
may never terminate, even after sending it SIGKILL---e.g., kthreadd on Linux."
(catch 'system-error
(lambda ()
(linux-kernel-thread? pid))
(const #f)))
(const #f)))
(define (processes)
"Return the list of live processes."
(sort (filter-map (lambda (file)
(let ((pid (string->number file)))
(and pid
(not (kernel? pid))
(not (pseudo-process? pid))
pid)))
(scandir "/proc"))
<))