From: Wenwu Hou <hwenwur@gmail.com>
To: Yosry Ahmed <yosry@kernel.org>
Cc: hannes@cmpxchg.org, nphamcs@gmail.com, chengming.zhou@linux.dev,
akpm@linux-foundation.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, stable@vger.kernel.org
Subject: Re: [PATCH] mm: zswap: set zswap_ever_enabled when enabling zswap at runtime
Date: Wed, 21 Oct 2026 10:01:35 +0800 [thread overview]
Message-ID: <atgc_4y2dA4egqXs@gmail.com> (raw)
In-Reply-To: <CAO9r8zNgnt=9UXN_FJ3zByVtC18MNe94-tXssAS-eAQfutNXRQ@mail.gmail.com>
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@gmail.com> 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@163.com/?
Yes, please drop this one, sorry for the noise.
prev parent reply other threads:[~2026-10-21 2:02 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-20 12:29 Wenwu Hou
2026-10-20 15:57 ` Yosry Ahmed
2026-10-21 2:01 ` Wenwu Hou [this message]
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