linux-kernel - Re: [PATCH] livepatch: add module locking around kallsyms calls

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Message-ID: <20150602100606.GA17412@dhcp-128-1.nay.redhat.com>
Date:	Tue, 2 Jun 2015 18:06:06 +0800
From:	Minfei Huang <mhuang@...hat.com>
To:	Miroslav Benes <mbenes@...e.cz>
Cc:	Minfei Huang <mnfhuang@...il.com>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	"sjenning@...hat.com" <sjenning@...hat.com>,
	Jiri Kosina <jkosina@...e.cz>,
	Vojtěch Pavlík <vojtech@...e.cz>,
	"live-patching@...r.kernel.org" <live-patching@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	pmladek@...e.cz
Subject: Re: [PATCH] livepatch: add module locking around kallsyms calls

On 06/02/15 at 11:15am, Miroslav Benes wrote:
> On Tue, 2 Jun 2015, Minfei Huang wrote:
> > > -       if (kallsyms_on_each_symbol(klp_verify_callback, &args))
> > > -               return 0;
> > > +       mutex_lock(&module_mutex);
> > > +       ret = kallsyms_on_each_symbol(klp_verify_callback, &args);
> > > +       mutex_unlock(&module_mutex);
> > >
> > 
> > Hi.
> > In livepatch code path, returning value 0 may represent the right, but
> > sometime represent wrong, like the above function.
> > 
> > Is it possible that we can wrap such function and return the unified
> > value? Thus we can not confuse the returning value any more.
> 
> Hi,
> 
> I must admit I do not understand. Both klp_find_object_symbol and 
> klp_verify_vmlinux_symbol return 0 on success or -EINVAL. It is true that 
> kallsyms_on_each_symbol and module_kallsyms_on_each symbol are different. 
> That is why our kallsyms callbacks are different. See the implementation 
> of those. But that is the API. Is this what you are worried about?
> 

Sorry to confuse you about the unclear description.

Yes. kallsyms_on_each_symbol return 0 to imply the failure. I know we
should comply the API which we call from the other module, but it may be
better to wrap the API as a function, if the return value conflicts with
current rule.

Otherwise it may confuse someone that the error message will be printed,
although the return value is 0, like kallsyms_on_each_symbol.

But I do not insist my view.

Thanks
Minfei

> > Otherwise annotation is appreciate.
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