re: kern/50430: syscall_disestablish() can remove active syscalls

[Paul Goyette <paul%vps1.whooppee.com@localhost>]

On Sun, 15 Nov 2015, Christos Zoulas wrote:

> Sure, that sounds prudent. ...

Also realize that disabling autounload won't prevent manual unloading
of modules via modunload(8).


>                      ... It is difficult to fix properly. One way to do
> this would be to mark all lwps that have used compat syscalls with a bit
> depending on the module they have used, and refuse to unload the module
> until the lwp is gone.
>
> - when load a module that has compat syscalls, assign to it a bit.
> - mark a flags field of all syscalls that were loaded with that module
>  with that bit.
> - or the lwp flags with the syscall flags on each syscall.
> - when it is time to unload check that no lwp has that bit in the flags
>  set.
> - instead of keeping l_sysent, keep l_sysmodflags or something.

It's not only "compat" modules that need to worry about this.  It is
potentially any unloadable module that uses syscall_establish().  (We
could skip allocating/setting the flag for built-in modules, but I
don't think that syscall_establish() is aware of this.)


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