Re: [PATCH v3] livepatch: Don't block removal of patches that are safe to unload

From: Petr Mladek
Date: Wed Mar 16 2022 - 11:01:11 EST


On Wed 2022-03-16 15:48:25, Miroslav Benes wrote:
> On Sat, 12 Mar 2022, Chengming Zhou wrote:
>
> > module_put() is not called for a patch with "forced" flag. It should
> > block the removal of the livepatch module when the code might still
> > be in use after forced transition.
> >
> > klp_force_transition() currently sets "forced" flag for all patches on
> > the list.
> >
> > In fact, any patch can be safely unloaded when it passed through
> > the consistency model in KLP_UNPATCHED transition.
> >
> > By other words, the "forced" flag must be set only for livepatches
>
> s/By/In/
>
> > that are being removed. In particular, set the "forced" flag:
> >
> > + only for klp_transition_patch when the transition to KLP_UNPATCHED
> > state was forced.
> >
> > + all replaced patches when the transition to KLP_PATCHED state was
> > forced and the patch was replacing the existing patches.
> >
> > index 5683ac0d2566..7f25a5ae89f6 100644
> > --- a/kernel/livepatch/transition.c
> > +++ b/kernel/livepatch/transition.c
> > @@ -641,6 +641,18 @@ void klp_force_transition(void)
> > for_each_possible_cpu(cpu)
> > klp_update_patch_state(idle_task(cpu));
> >
> > - klp_for_each_patch(patch)
> > - patch->forced = true;
> > + /*
> > + * Only need to set forced flag for the transition patch
> > + * when force transition to KLP_UNPATCHED state, but
> > + * have to set forced flag for all replaced patches
> > + * when force atomic replace transition.
> > + */
>
> How about something like
>
> /*
> * Set forced flag for patches being removed, which is the transition
> * patch in KLP_UNPATCHED state or all replaced patches when forcing
> * the atomic replace transition.
> */

Or just the first sentence:

/* Set forced flag for patches being removed */

The rest is visible from the code.

Either version works for me. If we agree on it then I update
the text when pushing the patch.

Best Regards,
Petr