[PATCH] zsmalloc: Fix races between modifications of fullness and isolated

[Andrew Morton]

On Wed, 26 Jul 2023 06:59:20 +0000 Andrew Yang (楊智強) <Andrew.Yang at mediatek.com> wrote:

> > Have you observed issues in real life? That commit is more than a
> > year
> > and a half old, so I wonder.
> > 
> Yes, we encountered many kernel exceptions of
> VM_BUG_ON(zspage->isolated == 0) in dec_zspage_isolation() and
> BUG_ON(!pages[1]) in zs_unmap_object() lately.
> This issue only occurs when migration and reclamation occur at the
> same time. With our memory stress test, we can reproduce this issue
> several times a day. We have no idea why no one else encountered
> this issue. BTW, we switched to the new kernel version with this
> defect a few months ago.

Ah.  It's important that such information be in the changelog!

I have put this info into my copy of the v1 patch's changelog.

I have moved the v1 patch from the mm-unstable branch into
mm-hotfixes-unstable, so it is staged for merging in this -rc cycle.

I have also added a cc:stable so that the fix gets backported into
kernels which contain c4549b871102.

I have added a note-to-self that a v2 patch is expected.