Hi,
On 2022/3/2 5:55 下午, Miroslav Benes wrote:
> 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.
Good point, I should check if it's an atomic replace livepatch in the else
branch, in which case we have to set all existing patches to forced.
Thanks.
>
> Miroslav
