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Date: Thu, 4 Feb 2016 17:47:57 +0100 (CET)
From: Miroslav Benes <mbenes@suse.cz>
To: Petr Mladek <pmladek@suse.com>
cc: Jessica Yu <jeyu@redhat.com>, Josh Poimboeuf <jpoimboe@redhat.com>,
        Seth Jennings <sjenning@redhat.com>, Jiri Kosina <jikos@kernel.org>,
        Vojtech Pavlik <vojtech@suse.com>,
        Rusty Russell <rusty@rustcorp.com.au>,
        Steven Rostedt <rostedt@goodmis.org>, Ingo Molnar <mingo@redhat.com>,
        live-patching@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 2/2] livepatch/module: remove livepatch module
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On Thu, 4 Feb 2016, Petr Mladek wrote:

> On Mon 2016-02-01 20:17:36, Jessica Yu wrote:
> >
> >  
> > -	if (patch->state == KLP_DISABLED)
> > -		goto disabled;
> > +			ret = klp_init_object_loaded(patch, obj);
> > +			if (ret) {
> > +				pr_warn("failed to initialize patch '%s' for module '%s' (%d)\n",
> > +					patch->mod->name, obj->mod->name, ret);
> > +				goto err;
> > +			}
> > +
> > +			if (patch->state == KLP_DISABLED)
> > +				break;
> >  
> > -	pr_notice("reverting patch '%s' on unloading module '%s'\n",
> > -		  pmod->name, mod->name);
> > +			pr_notice("applying patch '%s' to loading module '%s'\n",
> > +				  patch->mod->name, obj->mod->name);
> >  
> > -	klp_disable_object(obj);
> > +			ret = klp_enable_object(obj);
> > +			if (ret) {
> > +				pr_warn("failed to apply patch '%s' to module '%s' (%d)\n",
> > +					patch->mod->name, obj->mod->name, ret);
> > +				goto err;
> > +			}
> > +
> > +			break;
> > +		}
> > +	}
> > +
> > +	mutex_unlock(&klp_mutex);
> >  
> > -disabled:
> > -	klp_free_object_loaded(obj);
> > +	return 0;
> > +
> > +err:
> > +	/*
> > +	 * If a patch is unsuccessfully applied, return
> > +	 * error to the module loader.
> > +	 */
> > +	obj->mod = NULL;
> > +	pr_warn("patch '%s' is in an inconsistent state!\n", patch->mod->name);
> 
> This message is not correct. The module will not get loaded
> when the patch is not applied.

Yes, because we are in a better situation with this patch. We actually 
return an error and refuse to load the module. Message should take that 
into account.

> Instead, we need to revert all the operations that has already
> been done for this module. Note that the module stayed loaded
> before, so we did not need to release any memory or revert
> any ftrace call registration but we need to do so now!

Actually, I think the code is correct. If klp_init_object_loaded() there 
is no problem because we only write relocations there (which are written 
to the module being loaded) and resolve symbols via kallsyms. Nothing to 
revert there and it could be done again.

If klp_enable_object() fails, all the relevant error handling was already 
done there. See the call to klp_disable_object() if klp_enable_function() 
fails there.

Miroslav