On Wed, 7 Feb 2024 11:54:06 +0000 chengming.zhou@xxxxxxxxx wrote:
> From: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
>
> We may encounter duplicate entry in the zswap_store():
>
> 1. swap slot that freed to per-cpu swap cache, doesn't invalidate
> the zswap entry, then got reused. This has been fixed.
>
> 2. !exclusive load mode, swapin folio will leave its zswap entry
> on the tree, then swapout again. This has been removed.
>
> 3. one folio can be dirtied again after zswap_store(), so need to
> zswap_store() again. This should be handled correctly.
>
> So we must invalidate the old duplicate entry before insert the
> new one, which actually doesn't have to be done at the beginning
> of zswap_store(). And this is a normal situation, we shouldn't
> WARN_ON(1) in this case, so delete it. (The WARN_ON(1) seems want
> to detect swap entry UAF problem? But not very necessary here.)
>
> The good point is that we don't need to lock tree twice in the
> store success path.
>
> Note we still need to invalidate the old duplicate entry in the
> store failure path, otherwise the new data in swapfile could be
> overwrite by the old data in zswap pool when lru writeback.
>
> We have to do this even when !zswap_enabled since zswap can be
> disabled anytime. If the folio store success before, then got
> dirtied again but zswap disabled, we won't invalidate the old
> duplicate entry in the zswap_store(). So later lru writeback
> may overwrite the new data in swapfile.
>
> Fixes: 42c06a0e8ebe ("mm: kill frontswap")
> Cc: <stable@xxxxxxxxxxxxxxx>
We have a patch ordering issue.
As a cc:stable hotfix, this should be merged into 6.8-rcX and later
backported into -stable trees. So it will go
mm-hotfixes-unstable->mm-hotfixes-stable->mainline. So someone has to
make this patch merge and work against latest mm-hotfixes-unstable.
The patch you sent appears to be based on linux-next, so it has
dependencies upon mm-unstable patches which won't be merged into
mainline until the next merge window.
So can you please redo and retest this against mm.git's
mm-hotfixes-unstable branch? Then I'll try to figure out how to merge
the gigentic pile of mm-unstable zswap changes on top of that.
Thanks.
