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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 <[email protected]>
Message-ID: <[email protected]>
Signed-off-by: Dominique Martinet <[email protected]>
This commit is contained in:
Gui-Dong Han authored and Dominique Martinet committed 2026-06-21 05:22:57 +00:00
1 parent cc8b15a2c4
commit aa88278693
1 file changed
+5
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net/9p/trans_virtio.c
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@@ -532,6 +532,11 @@ req_retry_pinned:
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))