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Tue, 20 Oct 2026 19:02:10 -0700 (PDT) Received: from gmail.com ([43.224.245.234]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-8a0895fa6c6sm219573b3a.48.2026.10.20.19.02.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 20 Oct 2026 19:02:08 -0700 (PDT) Date: Wed, 21 Oct 2026 10:01:35 +0800 From: Wenwu Hou To: Yosry Ahmed 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 Message-ID: References: <20261020122942.3477541-1-hwenwur@gmail.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Tue, Oct 20, 2026 at 08:57:15AM -0700, Yosry Ahmed wrote: > On Tue, Oct 20, 2026 at 5:30 AM Wenwu Hou 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.