Hi,
On Tue, 1 Mar 2022, Chengming Zhou wrote:
> module_put() is currently never called for a patch with forced flag, to block
> the removal of that patch module that might still be in use after a forced
> transition.
>
> But klp_force_transition() will flag all patches on the list to be forced, since
> commit d67a53720966 ("livepatch: Remove ordering (stacking) of the livepatches")
> has removed stack ordering of the livepatches, it will cause all other patches can't
> be unloaded after disabled even if they have completed the KLP_UNPATCHED transition.
>
> In fact, we don't need to flag a patch to forced if it's a KLP_PATCHED forced
> transition. It can still be unloaded only if it has passed through the consistency
> model in KLP_UNPATCHED transition.
>
> So this patch only set forced flag and block the removal of a KLP_UNPATCHED forced
> transition livepatch.
>
> Signed-off-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
> ---
> kernel/livepatch/transition.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
> index 5683ac0d2566..8b296ad9e407 100644
> --- a/kernel/livepatch/transition.c
> +++ b/kernel/livepatch/transition.c
> @@ -641,6 +641,6 @@ 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;
> + if (klp_target_state == KLP_UNPATCHED)
> + klp_transition_patch->forced = true;
I do not think this would interact nicely with the atomic replace feature.
If you force the transition of a patch with ->replace set to true, no
existing patch would get ->forced set with this change, which means all
patches will be removed at the end of klp_try_complete_transition(). And
that is something we want to prevent.
Miroslav
