GNU bug report logs - #66151
29.1.50; daemon crashing after X forwarding disconnects

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From: George P <georgepanagopo <at> gmail.com>
To: 66151 <at> debbugs.gnu.org
Cc: "luangruo <at> yahoo.com" <luangruo <at> yahoo.com>, "eliz <at> gnu.org" <eliz <at> gnu.org>, "bschwehn <at> gmail.com" <bschwehn <at> gmail.com>
Subject: bug#66151: 29.1.50; daemon crashing after X forwarding disconnects
Date: Tue, 9 Apr 2024 20:36:33 +0000

Hi,

I am able to reproduce this bug without launching a new emacsclient.
Steps to reproduce:

- Start emacs daemon.
- Connect using emacsclient -c.
- Connect remotely to the daemon and run another emacsclient -c using X forwarding.
- Crash the X forwarding connection created in the previous step.
- Go back to the emacsclient running locally on the daemon and run
(set-fontset-font t '(#xe000 . #xf8ff) "Symbols Nerd Font Mono")

The reason why Ben was seeing a crash with a new emacsclient is because he is using Doom (an Emacs framework) that attached a function to server-after-make-hook that called set-fontset-font in the above way. As Eli said, there is really no good reason to run such a hook after the first frame, and this behavior has been fixed in Doom. (To Ben: try upgrading Doom and see if it fixes your issue, if not let me know!)

Surprisingly, the segfault still happens even if I explicitly call delete-frame on the dead frame before calling set-fontset-font. Also, I am unable to reproduce this bug without Doom (i.e. launching the daemon with -Q).

I am confused as to why emacs doesn't automatically clean up frames that have been disconnected like this. If emacs survives a crash of the X server, it should be able to identify that the display is dead (e.g. by checking the validity of output_data.x) and remove it from the (frame-list), preventing any subsequent commands from acting on these frames. It has to do something more than what delete-frame does, as that does not fix the issue (even though it removes the frame from the (frame-list)).

Note: using GTK is very different, as emacs crashes *without* having to run set-fontset-font (i.e. emacs crashes when the X forwarding connection crashes). With lucid, emacs continues to run fine with the exception of this bug for me.

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