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 <hanguidong02@gmail.com>
---
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 = 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))
--
2.34.1