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Sun, 25 Oct 2026 09:11:36 -0700 (PDT) Received: from asahi.tail4da9e3.ts.net ([218.48.198.193]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-369e8daa3a8sm21919868eec.16.2026.10.25.09.11.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 25 Oct 2026 09:11:36 -0700 (PDT) From: "Baek Kyu, Kim" To: Jens Axboe Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, "Baek Kyu, Kim" Subject: [PATCH] null_blk: reset cache state before device setup Date: Mon, 26 Oct 2026 01:11:33 +0900 Message-ID: <20261025161133.59344-1-pocj8ur4in@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-Transfer-Encoding: 8bit The CACHE flag belongs to nullb_device, which outlives each powered-on nullb instance. Power-off discards the runtime cache but leaves the flag set. If cache_size changes from 1 to 0 before the next power-on, the queue advertises write-through while new page writes still go into the cache tree. A completed write can then disappear at the next power-off. Clear CACHE before creating the new instance. The existing cache_size setup sets it again when the new instance needs a cache. Signed-off-by: Baek Kyu, Kim --- Tested under ARM64 QEMU/KVM through configfs and the null_blk block device. After changing cache_size from 1 to 0, a 4 KiB direct write to a new page read back immediately on both kernels. After a power cycle, the baseline lost the pattern while the kernel with this CACHE change retained all 4 KiB. Both queues advertised write-through. drivers/block/null_blk/main.c | 1 + 1 file changed, 1 insertion(+) diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c index 6beb1f5b71ac..ec0d7ba4d938 100644 --- a/drivers/block/null_blk/main.c +++ b/drivers/block/null_blk/main.c @@ -1976,6 +1976,7 @@ static int null_add_dev(struct nullb_device *dev) rv = null_validate_conf(dev); if (rv) return rv; + clear_bit(NULLB_DEV_FL_CACHE, &dev->flags); nullb = kzalloc_node(sizeof(*nullb), GFP_KERNEL, dev->home_node); if (!nullb) {