Re: [PATCH v3 2/2] liveupdate: initialize incoming FLB state before finish

[Pratyush Yadav <pratyush@kernel.org>]

On Thu, Apr 02 2026, Andrew Morton wrote:

> On Thu, 02 Apr 2026 13:28:33 +0000 Pratyush Yadav <pratyush@kernel.org> wrote:
>
>> The state of an incoming FLB object is initialized when it is first
>> used. The initialization is done via luo_flb_retrieve_one(), which looks
>> at all the incoming FLBs, matches the FLB to its serialized entry, and
>> initializes the incoming data and count.
>> 
>> luo_flb_file_finish_one() is called when finish is called for a file
>> registered with this FLB. If no file handler has used the FLB by this
>> point, the count stays un-initialized at 0. luo_flb_file_finish_one()
>> then decrements this un-initialized count, leading to an underflow. This
>> results in the FLB finish never being called since the count has
>> underflowed to a very large value.
>> 
>> Fix this by making sure the FLB is retrieved before using its count.
>
> I like that the above tells people what the actual bug is!
>
> I still have both Leo's patches in mm.git, in wait-and-see mode.  What
> to do here?  Should I upstream [1/2] and drop [2/2]?  Drop both and
> revisit after -rc1?

These are independent fixes, so I would suggest keeping 1/2 regardless
of what we do with 2/2. For 2/2, I would suggest replacing it with the
version I sent in <2vxzmrzlfq4e.fsf@kernel.org>.

Mike/Pasha/Leo, if you could review my version then that would be great.

Also Leo, please help with testing. I don't have a setup ready for
testing this corner case. I can set something up mid next week, but it
would be great if you can test this before that.

>
> Also, did we consider cc:stable for these two?  Perhaps add the
> cc:stable if we decide to attend to this after -rc1?

FLB landed in v7.0-rc1 so no need for cc:stable for patch 2/2. For patch
1/2, I think cc:stable does make sense, but it only landed in v6.19 so
not super important given it is not LTS.

-- 
Regards,
Pratyush Yadav