Re: bug#28544: 26.0.50; emacs will consume 100% cpu after gdb debugee exits

[sk6875@gmail.com]

On Friday, September 22, 2017 at 3:18:10 AM UTC+9, Sung Ho Kim wrote:
> First time using the bug report system, so apologies in advance if the
> report feels muddled.
> 
> The procedure I had used is as follows:
> 1) open emacs [-Q] [-nw]
>    N.B. the option flags -Q -nw do not make any difference in the
>    behavior described.
> 2) run gdb using M-x gdb ( I have tested gdb 7.12 and 8.0, 8.0.1 and
>    even earlier versions but gdb version do not seem to make any difference)
> 3) open any executable binary for debugging.
> 4) continue, step, next or run until binary in step (3) finishes
>    execution and exits (whether it exits normally or abnormally does not
>    make a difference)
> 5) open top and watch emacs cpu usage.
> 
> What I have noticed with a little bit of debugging and looking at the
> emacs source code is that in process.c in about line 5660 (thankfully
> process.c receives very little changes recently so the line number
> should be approximately accurate) you see the following code:
> -------------------------------------------------------------------
> 	      /* If we can detect process termination, don't consider the
> 		 process gone just because its pipe is closed.  */
> 	      else if (nread == 0 && !NETCONN_P (proc) && !SERIALCONN_P (proc)
> 		       && !PIPECONN_P (proc))
> -------------------------------------------------------------------
> This if clause becomes true when the debugee exits in Mac OS Sierra
> (10.12.6, BuildVersion 16G29, Darwin Kernel Version 16.7.0) and since
> nothing is done about the read file descriptor (proc's infd, outfd,
> channel) this results in an infinite loop where thread_select keeps
> returning nfds = 1 but the subsequent read operation will not return an
> error (i.e. nread will never be < 0) and nread will always be 0.  I feel
> this infinite loop is the cause of the 100% cpu usage behavior.
> 
> To test this theory, I added the same code used in the
> (nread == -1 && errno == EIO) condition to the
> (nread == 0 && !NETCONN_P (proc) && !SERIALCONN_P (proc) && !PIPECONN_P(proc))
> condition to remove the target file descriptor when this condition is
> encountered as such:
> 
> 	      else if (nread == 0 && !NETCONN_P (proc) && !SERIALCONN_P (proc)
> 		       && !PIPECONN_P (proc))
> #ifdef DARWIN_OS
> 		{
> 		  struct Lisp_Process *p = XPROCESS (proc);
> 
> 		  /* Clear the descriptor now, so we only raise the
> 		     signal once.  */
> 		  delete_read_fd (channel);
> 
> 		  if (p->pid == -2)
> 		    {
> 		      /* If the EIO occurs on a pty, the SIGCHLD handler's
> 			 waitpid call will not find the process object to
> 			 delete.  Do it here.  */
> 		      p->tick = ++process_tick;
> 		      pset_status (p, Qfailed);
> 		    }
> 		}
> #else
>                 ;
> #endif /* DARWIN_OS */
> 
> after rebuilding with the aforementioned change, the 100% cpu usage
> disappears.  I have refrained from offering a patch because I am not
> fully knowledgeable with the code and its possible side effects.
> 
> Thank you for your patience and your great work developing this great OS.
> 
> 
> In GNU Emacs 26.0.50 (build 2, x86_64-apple-darwin16.7.0)
>  of 2017-09-20 built on dana.local
> Repository revision: bc511a64f6da9ab51acc7c8865e80c4a4cb655c2
> Recent messages:
> applying putty GNU screen fixes.
> Reusing Dired buffers is now ON
> Turning on magit-auto-revert-mode...done
> ad-handle-definition: ‘compilation-start’ got redefined
> For information about GNU Emacs and the GNU system, type C-h C-a.
> 
> Configured using:
>  'configure --prefix=/opt/local/emacs-git --without-makeinfo
>  --without-ns --without-pop --without-mailutils'
> 
> Configured features:
> DBUS NOTIFY ACL GNUTLS LIBXML2 ZLIB
> 
> Important settings:
>   value of $LC_ALL: en_US.UTF-8
>   locale-coding-system: utf-8-unix
> 
> Major mode: Fundamental
> 
> Minor modes in effect:
>   diff-auto-refine-mode: t
>   magit-auto-revert-mode: t
>   global-git-commit-mode: t
>   async-bytecomp-package-mode: t
>   shell-dirtrack-mode: t
>   bury-successful-compilation: t
>   global-auto-complete-mode: t
>   cl-old-struct-compat-mode: t
>   tooltip-mode: t
>   global-eldoc-mode: t
>   electric-indent-mode: t
>   menu-bar-mode: t
>   file-name-shadow-mode: t
>   global-font-lock-mode: t
>   auto-composition-mode: t
>   auto-encryption-mode: t
>   auto-compression-mode: t
>   buffer-read-only: t
>   line-number-mode: t
>   transient-mark-mode: t
> 
> Load-path shadows:
> ~/.emacs.d/lisp/expand-region-core hides /Users/sk68/.emacs.d/elpa/expand-region-0.11.0/expand-region-core
> ~/.emacs.d/lisp/linum hides /opt/local/emacs-git/share/emacs/26.0.50/lisp/linum
> 
> Features:
> (shadow sort mail-extr emacsbug sendmail term/xterm xterm flymake
> flymake-proc compile flymake-ui display-line-numbers elec-pair
> magit-obsolete magit-blame magit-stash magit-bisect magit-remote
> magit-commit magit-sequence magit-notes magit-worktree magit-branch
> magit-files magit-refs magit-status magit magit-repos magit-apply
> magit-wip magit-log magit-diff smerge-mode diff-mode magit-core
> magit-autorevert autorevert filenotify magit-process magit-margin
> magit-mode magit-git magit-section magit-popup git-commit magit-utils
> crm log-edit message subr-x puny rfc822 mml mml-sec epa epg gnus-util
> rmail rmail-loaddefs time-date mm-decode mm-bodies mm-encode mail-parse
> rfc2231 rfc2047 rfc2045 mm-util ietf-drums mail-prsvr mailabbrev
> mail-utils gmm-utils mailheader pcvs-util add-log with-editor cl-extra
> async-bytecomp async shell pcomplete comint ansi-color ring server dash
> help-mode dired+ image-dired image-mode format-spec image-file image
> dired-x dired-aux dired dired-loaddefs cl findheader
> compilation-window-helper bury-successful-compilation advice
> auto-complete-config auto-complete popup ztree ztree-diff
> ztree-diff-model ztree-dir easy-mmode ztree-view edmacro kmacro
> ztree-util jison-mode bison-mode derived cc-mode cc-fonts cc-guess
> cc-menus cc-cmds cc-styles cc-align cc-engine cc-vars cc-defs regexp-opt
> finder-inf info tool-bar package easymenu epg-config url-handlers
> url-parse auth-source cl-seq eieio eieio-core cl-macs eieio-loaddefs
> password-cache url-vars seq byte-opt gv bytecomp byte-compile cconv
> cl-loaddefs cl-lib mule-util tooltip eldoc electric uniquify ediff-hook
> vc-hooks lisp-float-type tabulated-list replace newcomment text-mode
> elisp-mode lisp-mode prog-mode register page menu-bar rfn-eshadow
> isearch timer select mouse jit-lock font-lock syntax facemenu font-core
> term/tty-colors frame cl-generic 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 charscript charprop case-table epa-hook jka-cmpr-hook
> help simple abbrev obarray minibuffer cl-preloaded nadvice loaddefs
> button faces cus-face macroexp files text-properties overlay sha1 md5
> base64 format env code-pages mule custom widget hashtable-print-readable
> backquote dbusbind kqueue multi-tty make-network-process emacs)
> 
> Memory information:
> ((conses 16 267423 9498)
>  (symbols 48 33034 2)
>  (miscs 40 79 97)
>  (strings 32 73135 3249)
>  (string-bytes 1 2304657)
>  (vectors 16 29273)
>  (vector-slots 8 620415 7189)
>  (floats 8 124 327)
>  (intervals 56 240 0)
>  (buffers 992 12))

Any updates on this?