linux-kernel - Re: [PATCH] livepatch: Enhance livepatch to support remove patch module dynamically

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Message-ID: <alpine.LNX.2.00.1504011612460.843@pobox.suse.cz>
Date:	Wed, 1 Apr 2015 16:13:31 +0200 (CEST)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Minfei Huang <mnfhuang@...il.com>
cc:	jpoimboe@...hat.com, sjenning@...hat.com, vojtech@...e.cz,
	live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] livepatch: Enhance livepatch to support remove patch
 module dynamically

On Wed, 1 Apr 2015, Minfei Huang wrote:

> > > diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> > > index 3f9f1d6..0266950 100644
> > > --- a/kernel/livepatch/core.c
> > > +++ b/kernel/livepatch/core.c
> > > @@ -502,6 +502,17 @@ static int __klp_disable_patch(struct klp_patch *patch)
> > >       return 0;
> > >  }
> > >
> > > +static int __klp_disable_patch_nolock(struct klp_patch *patch)
> > > +{
> > > +     int ret = 0;
> > > +
> > > +     ret = __klp_disable_patch(patch);
> > > +     if (ret)
> > > +             return ret;
> > > +     module_put(patch->mod);
> > > +     return ret;
> > > +}
> > > +
> >
> > Your patch doesn't solve the problem at all.
> >
> > There is no guarantee that once __klp_disable_patch() returns noone is
> > using the old code any more.
> >
> 
> Yes, thanks.
> 
> The __klp_disable_patch only guarantees that we will never call the
> function in patch module. For now, patch module can never be removed
> from the kernel once it was loaded. It may be inconvenience if we want
> re-load a new patch module replace the old patch module.

Patch stacking is possible though.

-- 
Jiri Kosina
SUSE Labs
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