bug#29275: dynamic-link hangs on error

bug#29275: dynamic-link hangs on error

[noxdafox]

Greetings,

I am trying to call some C function which seems not to be included in 
Guile library (fnmatch).

If dynamic-link is given wrong library objects, it will hang forcing the 
user to kill the VM as it becomes unresponsive.

I could find at least 2 ways to reproduce it:

1. Calling dynamic-link on a wrong object

2. Calling dynamic-link subsequently on 2 non existing objects

Here's an example:

GNU Guile 2.2.2
Copyright (C) 1995-2017 Free Software Foundation, Inc.

Guile comes with ABSOLUTELY NO WARRANTY; for details type `,show w'.
This program is free software, and you are welcome to redistribute it
under certain conditions; type `,show c' for details.

Enter `,help' for help.
scheme@(guile-user)> (use-modules (system foreign))
scheme@(guile-user)> (define libc-obj (dynamic-link "nonexisting"))
ERROR: In procedure dynamic-link:
ERROR: In procedure dynamic-link: file: "nonexisting", message: "file 
not found"

Entering a new prompt.  Type `,bt' for a backtrace or `,q' to continue.
scheme@(guile-user) [1]> (define libc-obj (dynamic-link "nonexisting"))

^^^ here the VM becomes unresponsive.

bug#29275: dynamic-link hangs on error

[Ludovic Courtès]

Hello,

noxdafox <noxdafox@gmail.com> skribis:

> GNU Guile 2.2.2
> Copyright (C) 1995-2017 Free Software Foundation, Inc.
>
> Guile comes with ABSOLUTELY NO WARRANTY; for details type `,show w'.
> This program is free software, and you are welcome to redistribute it
> under certain conditions; type `,show c' for details.
>
> Enter `,help' for help.
> scheme@(guile-user)> (use-modules (system foreign))
> scheme@(guile-user)> (define libc-obj (dynamic-link "nonexisting"))
> ERROR: In procedure dynamic-link:
> ERROR: In procedure dynamic-link: file: "nonexisting", message: "file
> not found"
>
> Entering a new prompt.  Type `,bt' for a backtrace or `,q' to continue.
> scheme@(guile-user) [1]> (define libc-obj (dynamic-link "nonexisting"))
>
> ^^^ here the VM becomes unresponsive.

This is because libguile synchronizes uses of ‘dynamic-link’ with a
non-recursive mutex.  Here, the “inner” ‘dynamic-link’ call occurs while
the mutex is already held by the calling thread, which is why it just
hangs.

Fixed in commit 48d42553ef5a9c2240bc2296d1b38dbfd5fca1ac, which will be
in the next 2.2 release.

Thanks,
Ludo’.