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Bug#1151281: ✔️Re: Bug#1151281: linux-image-6.12.113+deb13-amd64: kswapd NULL pointer dereference in list_lru_add() (workingset_update_node), system freeze

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  Bug#1151281: ✔️Re: Bug#1151281: linux-image-6.12.113+deb13-amd64: kswapd NULL pointer dereference in list_lru_add() (workingset_update_node), system freeze Salvatore Bonaccorso <carnil@debian.org> - 2026-10-19 23:00 +0200

#94538 — Bug#1151281: ✔️Re: Bug#1151281: linux-image-6.12.113+deb13-amd64: kswapd NULL pointer dereference in list_lru_add() (workingset_update_node), system freeze

Control: tags -1 + moreinfo

Hi Thomas,

On Mon, Oct 19, 2026 at 02:57:43PM +0000, Thomas MISCHLER - API AND YOU wrote:
> Two corrections to my initial report.
> 
> 1. Suggested fix: aca1f2d5de17 does not apply as is to 6.12.y. Its
>    Fixes: target is the non-uniform __folio_split() (58729c04cf10, 6.15+).
>    In 6.12.y the page-cache split goes through
>    split_huge_page_to_list_to_order(), which calls xas_split_alloc()
>    without mapping_set_update() (mm/huge_memory.c in v6.12.113).
>    So the options for 6.12.y are rather:
>     - revert ad812805fea7 ("xarray: honor XA_FLAGS_ACCOUNT in
>       xas_split_alloc()"), or
>     - an adapted fix: mapping_set_update(&xas, mapping) before
>       xas_split_alloc() in split_huge_page_to_list_to_order(). Note that
>       in 6.12.y mapping_set_update() is still a static function in
>       mm/filemap.c (it only moved to mm/internal.h in 6.13), so this
>       also needs that move or an open-coded equivalent.
>    Neither has been tested on our side.
> 
> 2. Upstream report: I wrote that we would report this to
>    stable@vger.kernel.org. We will not contact upstream ourselves; we
>    leave it to you to forward it if you confirm it is not Debian-specific,
>    or to ask us to do it (a draft for stable@ / regressions@ is ready).
> 
> We have an affected guest available to test a patched kernel (booted
> without cgroup.memory=nokmem).

Please test with a pristine build of 6.12.113 (i.e. withouth Debian
patches on top). If you can reproduce the issue, please forward it
upstream (and report here where it has been reported).

In case you can quickly trigger the behaviour, it would be helpful for
the upstream report if you bisect the changes and confirm your
suspected breaking change.

Thank you already,

Regards,
Salvatore

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