Re: [PATCH] mm: zswap: set zswap_ever_enabled when enabling zswap at runtime

[Wenwu Hou]

On Tue, Oct 20, 2026 at 08:57:15AM -0700, Yosry Ahmed wrote:
> On Tue, Oct 20, 2026 at 5:30 AM Wenwu Hou <hwenwur@xxxxxxxxx> wrote:
> >
> > zswap can end up enabled without zswap_ever_enabled being set, which
> > leads to data corruption. With CONFIG_ZSWAP_DEFAULT_ON=n:
> >
> > 1. zswap_setup() fails to create the initial pool. Setup still counts
> >    as successful, but zswap_has_pool stays false.
> > 2. The user writes a compressor name to
> >    /sys/module/zswap/parameters/compressor.
> >    zswap_compressor_param_set() creates a pool and sets
> >    zswap_has_pool = true, but never enables the zswap_ever_enabled
> >    static key.
> > 3. The user runs "echo Y > /sys/module/zswap/parameters/enabled".
> > 4. zswap_store() now stores pages in zswap, and swap_writeout() skips
> >    writing them to the swap device.
> > 5. On swap-in, zswap_load() first checks zswap_never_enabled(). It
> >    returns true, so zswap_load() reports that the page is not in zswap.
> >    The page is then read from the swap device, which holds stale data.
> >
> > Fix this by enabling zswap_ever_enabled in zswap_enabled_param_set()
> > before zswap_enabled becomes true.
> 
> Wasn't this fixed by
> https://lore.kernel.org/linux-mm/20260906133601.3563324-1-xialonglong2025@xxxxxxx/?

Yes, please drop this one, sorry for the noise.