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([163.61.198.28]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-c85772d9d35sm975539a12.29.2026.05.29.00.55.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 29 May 2026 00:55:29 -0700 (PDT) From: Gui-Dong Han To: ericvh@kernel.org, lucho@ionkov.net, asmadeus@codewreck.org Cc: linux_oss@crudebyte.com, v9fs@lists.linux.dev, linux-kernel@vger.kernel.org, baijiaju1990@gmail.com, Gui-Dong Han Subject: [PATCH] 9p: Add missing read barrier in virtio zero-copy path Date: Fri, 29 May 2026 15:54:41 +0800 Message-Id: <20260529075441.233369-1-hanguidong02@gmail.com> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Commit 2b6e72ed747f ("9P: Add memory barriers to protect request fields over cb/rpc threads handoff") added a read barrier after p9_client_rpc() waits for req->status, pairing with the write barrier in p9_client_cb(). The virtio zero-copy wait path was missed. Add the same read barrier after the zero-copy wait before reading the completed request. Fixes: abfa034e4b8e ("fs/9p: Update zero-copy implementation in 9p") Signed-off-by: Gui-Dong Han --- Found by auditing READ_ONCE() used for synchronization. A similar fix can be found in 8df672bfe3ec. --- net/9p/trans_virtio.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c index 4cdab7094b27..b0d0094ec8e2 100644 --- a/net/9p/trans_virtio.c +++ b/net/9p/trans_virtio.c @@ -532,6 +532,11 @@ p9_virtio_zc_request(struct p9_client *client, struct = p9_req_t *req, p9_debug(P9_DEBUG_TRANS, "virtio request kicked\n"); err =3D io_wait_event_killable(req->wq, READ_ONCE(req->status) >=3D REQ_STATUS_RCVD); + /* + * Make sure our req is coherent with regard to updates in other + * threads - echoes to wmb() in the callback + */ + smp_rmb(); // RERROR needs reply (=3D=3D error string) in static data if (READ_ONCE(req->status) =3D=3D REQ_STATUS_RCVD && unlikely(req->rc.sdata[4] =3D=3D P9_RERROR)) --=20 2.34.1