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9p: Add missing read barrier in virtio zero-copy path

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Commit 2b6e72ed74 ("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: 2b6e72ed74 ("9P: Add memory barriers to protect request fields over cb/rpc threads handoff")
Signed-off-by: Gui-Dong Han <hanguidong02@gmail.com>
Message-ID: <20260529075441.233369-1-hanguidong02@gmail.com>
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
This commit is contained in:
Gui-Dong Han
2026-05-29 15:54:41 +08:00
committed by Dominique Martinet
parent cc8b15a2c4
commit aa88278693
1 changed files with 5 additions and 0 deletions
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5
net/9p/trans_virtio.c
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@@ -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))