bug#69529: 29.2; Segfault killing base buffer when the indirect buffer rejects kill-buffer

bug#69529: 29.2; Segfault killing base buffer when the indirect buffer rejects kill-buffer

[brubar.cs]

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Emacs segfaults when evaluating the attached elisp file like this:

   emacs -Q -l kill-buffer-segfault.el

It happens to me, both with GNU Emacs 30.0.50 and 29.2.

Let me know if you need me to collect more information locally.

Thanks,

Bruno


[-- Attachment #2: kill-buffer-segfault.el --]
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(defun my-reject-kill-buffer ()
  (message "Do not kill %s" (current-buffer))
  nil)

(defun my-trigger-bug ()
  (let* ((base-buffer (generate-new-buffer "base"))
	 (indirect-buffer (make-indirect-buffer base-buffer
						(generate-new-buffer-name "indirect"))))

    ;; base-buffer: no restriction on killing that buffer.
    (with-current-buffer base-buffer
      (insert "base buffer content")
      (setq-local kill-buffer-query-functions nil))

    ;; indirect-buffer: reject any kill-buffer requests
    (with-current-buffer indirect-buffer
      (insert "indirect buffer content")
      (setq-local kill-buffer-query-functions
		              (list 'my-reject-kill-buffer)))

    ;; Killing base-buffer
    (with-current-buffer base-buffer
      (kill-buffer))

    ;; This raises the segfault (emacs 29, emacs 30.0.50).
    (switch-to-buffer indirect-buffer)))

(my-trigger-bug)

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In GNU Emacs 29.2 (build 1, x86_64-pc-linux-gnu, cairo version 1.18.0)
 of 2024-03-02 built on localhost
Windowing system distributor 'The X.Org Foundation', version 11.0.12101011
System Description: Gentoo Linux

Configured using:
 'configure --prefix=/usr --build=x86_64-pc-linux-gnu
 --host=x86_64-pc-linux-gnu --mandir=/usr/share/man
 --infodir=/usr/share/info --datadir=/usr/share --sysconfdir=/etc
 --localstatedir=/var/lib --datarootdir=/usr/share
 --disable-silent-rules --docdir=/usr/share/doc/emacs-29.2-r1
 --htmldir=/usr/share/doc/emacs-29.2-r1/html --libdir=/usr/lib64
 --program-suffix=-emacs-29 --includedir=/usr/include/emacs-29
 --infodir=/usr/share/info/emacs-29 --localstatedir=/var
 --enable-locallisppath=/etc/emacs:/usr/share/emacs/site-lisp
 --without-compress-install --without-hesiod --without-pop
 --with-file-notification=inotify --with-pdumper --enable-acl
 --with-dbus --without-modules --without-gameuser --with-libgmp
 --with-gpm --with-native-compilation=aot --without-json
 --without-kerberos --without-kerberos5 --with-lcms2 --with-xml2
 --without-mailutils --without-selinux --without-sqlite3 --with-gnutls
 --without-libsystemd --with-threads --without-tree-sitter
 --without-wide-int --with-sound=no --with-zlib --with-x --without-pgtk
 --without-ns --without-gconf --without-gsettings
 --without-toolkit-scroll-bars --with-xpm --with-xft --with-cairo
 --without-harfbuzz --without-libotf --without-m17n-flt
 --with-x-toolkit=no --without-gif --with-jpeg --with-png --with-rsvg
 --with-tiff --without-webp --with-imagemagick --with-dumping=pdumper
 'CFLAGS=-march=native -O2 -pipe' 'LDFLAGS=-Wl,-O1 -Wl,--as-needed''

Configured features:
ACL CAIRO DBUS FREETYPE GLIB GMP GNUTLS GPM IMAGEMAGICK JPEG LCMS2
LIBXML2 NATIVE_COMP NOTIFY INOTIFY OLDXMENU PDUMPER PNG RSVG SECCOMP
THREADS TIFF X11 XDBE XIM XINPUT2 XPM ZLIB

Important settings:
  value of $LC_CTYPE: en_US.UTF-8
  value of $LANG: C.UTF8
  locale-coding-system: utf-8-unix

Major mode: Fundamental

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  show-paren-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  blink-cursor-mode: t
  buffer-read-only: t
  line-number-mode: t
  indent-tabs-mode: t
  transient-mark-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message mailcap yank-media puny dired
dired-loaddefs rfc822 mml mml-sec password-cache epa derived epg rfc6068
epg-config gnus-util text-property-search time-date mm-decode mm-bodies
mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail
rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils comp comp-cstr
subr-x rx cl-seq cl-macs gv cl-extra help-mode bytecomp byte-compile
warnings icons cl-loaddefs cl-lib site-gentoo rmc iso-transl tooltip
cconv eldoc paren electric uniquify ediff-hook vc-hooks lisp-float-type
elisp-mode mwheel term/x-win x-win term/common-win x-dnd tool-bar dnd
fontset image regexp-opt fringe tabulated-list replace newcomment
text-mode lisp-mode prog-mode register page tab-bar menu-bar rfn-eshadow
isearch easymenu timer select scroll-bar mouse jit-lock font-lock syntax
font-core term/tty-colors frame minibuffer nadvice seq simple cl-generic
indonesian philippine cham georgian utf-8-lang misc-lang vietnamese
tibetan thai tai-viet lao korean japanese eucjp-ms cp51932 hebrew greek
romanian slovak czech european ethiopic indian cyrillic chinese
composite emoji-zwj charscript charprop case-table epa-hook
jka-cmpr-hook help abbrev obarray oclosure cl-preloaded button loaddefs
theme-loaddefs faces cus-face macroexp files window text-properties
overlay sha1 md5 base64 format env code-pages mule custom widget keymap
hashtable-print-readable backquote threads dbusbind inotify lcms2
dynamic-setting font-render-setting cairo xinput2 x multi-tty
make-network-process native-compile emacs)

Memory information:
((conses 16 78936 6614)
 (symbols 48 7120 0)
 (strings 32 19234 2559)
 (string-bytes 1 580076)
 (vectors 16 15692)
 (vector-slots 8 321239 17561)
 (floats 8 34 120)
 (intervals 56 443 2)
 (buffers 976 12))

bug#69529: 29.2; Segfault killing base buffer when the indirect buffer rejects kill-buffer

[Eli Zaretskii]

> From: brubar.cs@gmail.com
> Date: Sun, 03 Mar 2024 18:37:53 +0100
> 
> Emacs segfaults when evaluating the attached elisp file like this:
> 
>    emacs -Q -l kill-buffer-segfault.el
> 
> It happens to me, both with GNU Emacs 30.0.50 and 29.2.

Stefan and Martin, is the below the right way of avoiding this?

diff --git a/src/buffer.c b/src/buffer.c
index 126f3eb..bccf65f 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -1971,8 +1971,14 @@ DEFUN ("kill-buffer", Fkill_buffer, Skill_buffer, 0, 1, "bKill buffer: ",
       Lisp_Object tail, other;
 
       FOR_EACH_LIVE_BUFFER (tail, other)
-	if (XBUFFER (other)->base_buffer == b)
-	  Fkill_buffer (other);
+	{
+	  if (XBUFFER (other)->base_buffer == b)
+	    {
+	      Fkill_buffer (other);
+	      if (BUFFER_LIVE_P (XBUFFER (other)))
+		error ("Attempt to kill buffer whose indirect buffer cannot be killed");
+	    }
+	}
 
       /* Exit if we now have killed the base buffer (Bug#11665).  */
       if (!BUFFER_LIVE_P (b))

bug#69529: 29.2; Segfault killing base buffer when the indirect buffer rejects kill-buffer

[Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors]

> Stefan and Martin, is the below the right way of avoiding this?

I don't know if it's The Right Way (I mean: who the hell does this
indirect buffer think he is, to resist killing?), but it looks fine
to me.


        Stefan

bug#69529: 29.2; Segfault killing base buffer when the indirect buffer rejects kill-buffer

[martin rudalics via Bug reports for GNU Emacs, the Swiss army knife of text editors]

> Stefan and Martin, is the below the right way of avoiding this?

I see no better way.

martin

bug#69529: 29.2; Segfault killing base buffer when the indirect buffer rejects kill-buffer

[Eli Zaretskii]

> Date: Mon, 4 Mar 2024 09:04:30 +0100
> Cc: 69529@debbugs.gnu.org
> From: martin rudalics <rudalics@gmx.at>
> 
> > Stefan and Martin, is the below the right way of avoiding this?
> 
> I see no better way.

Thanks, Stefan and Martin.  I installed the change on the master
branch, and I'm therefore closing this bug.