Re: [PATCH] module interface improvement for kprobes

From: Chuck Ebbert
Date: Fri Aug 04 2006 - 19:01:20 EST


In-Reply-To: <1154721061.15967.31.camel@xxxxxxxxxxxxxxxxxxxxx>

On Fri, 04 Aug 2006 14:51:01 -0500, David Smith wrote:

> > > I've added a new function, module_get_byname(), that looks up a module
> > > by name and returns the module reference. Note that module_get_byname()
> > > also increments the module reference count. It does this so that the
> > > module won't be unloaded between the time that module_get_byname() is
> > > called and register_kprobe() is called.

Your patch is word-wrapped.

Also:

> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -291,7 +291,27 @@ static struct module *find_module(const
> }
> return NULL;
> }
> +
> +int module_get_byname(const char *mod_name, struct module **mod)
> +{
> + *mod = NULL;
>
> + /* We must hold module_mutex before calling find_module(). */
> + if (mutex_lock_interruptible(&module_mutex) != 0)
> + return -EINTR;
> +
> + *mod = find_module(mod_name);
> + mutex_unlock(&module_mutex);
> + if (*mod) {
> + if (!strong_try_module_get(*mod)) {

What keeps the module from going away between the mutex_unlock() and
strong_try_module_get()? It needs to be something like this:

*mod = find_module(mod_name);
if (*mod)
ret = strong_try_module_get(*mod);
mutex_unlock(&module_mutex);
if (!ret) {
*mod = NULL;
return -EINVAL;
}

> + *mod = NULL;
> + return -EINVAL;
> + }
> + }
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(module_get_byname);
> +
> #ifdef CONFIG_SMP
> /* Number of blocks used and allocated. */
> static unsigned int pcpu_num_used, pcpu_num_allocated;

--
Chuck

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