Re: [Kernel Bug] INFO: task hung in zswap_decompress

[Yosry Ahmed]

On Tue, Jun 9, 2026 at 8:40 AM Nhat Pham <nphamcs@xxxxxxxxx> wrote:
>
> On Tue, Jun 9, 2026 at 4:51 AM Longxing Li <coregee2000@xxxxxxxxx> wrote:
> >
> > Dear Linux kernel developers and maintainers,
> >
> > We would like to report a new kernel bug found by our tool. INFO: task
> > hung in zswap_decompress. Details are as follows.
> >
> > Kernel commit: v7.0.6
> > Kernel config: see attachment
> > report: see attachment

If I am reading the report correctly, it seems like we are doing
swapin from the page fault path, and waiting for the per-CPU mutex
that is held by kswapd. Since we can sleep waiting for decompression
while holding the mutex, it's possible that we have some kind of
priority inversion where kswap held the lock, went to sleep, and
didn't run again for a while. But that always been possible for a long
time AFAICT.

Do you have any more details? Is this a new regression (observed when
upgrading to v7.0.6), or is it possible this was a pre-existing issue
and you just found it on this kernel?

> >
> > We are currently analyzing the root cause and  working on a
> > reproducible PoC. We will provide further updates in this thread as
> > soon as we have more information.

Yeah more details like a known-good kernel version, or even better a
reproducer, would certainly help a lot.

> >
> > Best regards,
> > Longxing Li
> >
> > ==================================================================
> > https://drive.google.com/file/d/1Bx2unEf-QntjVi8g6Zw7QNO6OP4cjGO_/view?usp=drive_link
> >
> > https://drive.google.com/file/d/16xzUrwOvwE67cnMPH3AhhNRWq6hr26Qj/view?usp=drive_link
>
> + Kanchana, who last worked on this piece of code