From aa88278693cbfaf7a2acf961379973fbb63b165c Mon Sep 17 00:00:00 2001 From: Gui-Dong Han Date: Fri, 29 May 2026 15:54:41 +0800 Subject: [PATCH] 9p: Add missing read barrier in virtio zero-copy path 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: 2b6e72ed747f ("9P: Add memory barriers to protect request fields over cb/rpc threads handoff") Signed-off-by: Gui-Dong Han Message-ID: <20260529075441.233369-1-hanguidong02@gmail.com> Signed-off-by: Dominique Martinet --- 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 = io_wait_event_killable(req->wq, READ_ONCE(req->status) >= 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 (== error string) in static data if (READ_ONCE(req->status) == REQ_STATUS_RCVD && unlikely(req->rc.sdata[4] == P9_RERROR))