io_uring/net: only import send_zc buffer once

io_send_zc() guards its call to io_send_zc_import() with if (!done_io)
in an attempt to avoid calling it redundantly on the same req. However,
if the initial non-blocking issue returns -EAGAIN, done_io will stay 0.
This causes the subsequent issue to unnecessarily re-import the buffer.

Add an explicit flag "imported" to io_sr_msg to track if its buffer has
already been imported. Clear the flag in io_send_zc_prep(). Call
io_send_zc_import() and set the flag in io_send_zc() if it is unset.

Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
Fixes: 54cdcca ("io_uring/net: switch io_send() and io_send_zc() to using io_async_msghdr")
Link: https://lore.kernel.org/r/20250321184819.3847386-2-csander@purestorage.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/net.c

@@ -77,6 +77,7 @@ struct io_sr_msg {
 	/* initialised and used only by !msg send variants */
 	u16				buf_group;
 	bool				retry;
+	bool				imported; /* only for io_send_zc */
 	void __user			*msg_control;
 	/* used only for send zerocopy */
 	struct io_kiocb 		*notif;
@@ -1306,6 +1307,7 @@ int io_send_zc_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 
 	zc->done_io = 0;
 	zc->retry = false;
+	zc->imported = false;
 	req->flags |= REQ_F_POLL_NO_LAZY;
 
 	if (unlikely(READ_ONCE(sqe->__pad2[0]) || READ_ONCE(sqe->addr3)))
@@ -1451,7 +1453,8 @@ int io_send_zc(struct io_kiocb *req, unsigned int issue_flags)
 	    (zc->flags & IORING_RECVSEND_POLL_FIRST))
 		return -EAGAIN;
 
-	if (!zc->done_io) {
+	if (!zc->imported) {
+		zc->imported = true;
 		ret = io_send_zc_import(req, issue_flags);
 		if (unlikely(ret))
 			return ret;