Re: [PATCH] add hook to read_from_oldmem() to check for non-ram pages

Andrew Morton
2011-05-06T19:30:27Z

On Fri, 6 May 2011 12:55:46 +0200
Olaf Hering <olaf@aepfle.de> wrote:

> Should the called code increase/decrease the modules refcount instead?
> I remember there was some MODULE_INC/MODULE_DEC macro (cant remember the
> exact name) at some point. What needs to be done inside the module to
> prevent an unload while its still in use? Is it __module_get/module_put
> for each call of fn()?

A try_module_get(THIS_MODULE) in the register function will do the trick.
However it's unneeded. Documentation/DocBook/kernel-hacking.tmpl tells us

try_module_get() module_put()

These manipulate the module usage count, to protect against
removal (a module also can't be removed if another module uses one
of its exported symbols: see below). Before calling into module
code, you should call <function>try_module_get()</function> on
that module: if it fails, then the module is being removed and you
should act as if it wasn't there. Otherwise, you can safely enter
the module, and call <function>module_put()</function> when you're
finished.

So as your module will have a reference to vmcore.c's register and unregister
functions, nothing needs to be done: the presence of the client module alone
will pin the vmcore.c module.

However it's all moot, because the fs/proc/vmcore.c code cannot
presently be built as a module and it's rather unlikely that it ever
will be.