There are two issues:
[1] data may change while ext4 is writing it to zram.
[2] zram is written directly without checking the length after recompression,
which may cause zs_obj to be damaged.
This patch solves [2].
as you said:
> zram cannot ensure that, it's not zram's job. Nothing stops
> the buggy actor from modifiying the page at any random point,
It is not zram's job to ensure that data is not modified.
As long as there is re-compression, it must be confirmed again
whether the length has changed. This way we can avoid zram
panic caused by upper layer problems.
So I think this patch should not be discarded.
As for issues [1], i'm powerless.
