Hi,
Static analysis with Coverity on linux-next detected a minor issue that
was introduced with the following commit:
commit cb261b594b4108668e00f565184c7c221efe0359
Author: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
Date: Wed May 19 17:07:44 2021 +0800
bpf: Run devmap xdp_prog on flush instead of bulk enqueue
The analysis is as follows:
370static void bq_xmit_all(struct xdp_dev_bulk_queue *bq, u32 flags)
371{
372 struct net_device *dev = bq->dev;
373 int sent = 0, drops = 0, err = 0;
374 unsigned int cnt = bq->count;
375 int to_send = cnt;
376 int i;
377
378 if (unlikely(!cnt))
379 return;
380
381 for (i = 0; i < cnt; i++) {
382 struct xdp_frame *xdpf = bq->q[i];
383
384 prefetch(xdpf);
385 }
386
387 if (bq->xdp_prog) {
388 to_send = dev_map_bpf_prog_run(bq->xdp_prog, bq->q,
cnt, dev);
389 if (!to_send)
390 goto out;
391
Unused value (UNUSED_VALUE)
assigned_value: Assigning value from cnt - to_send to drops here, but
that stored value is overwritten before it can be used.
392 drops = cnt - to_send;
393 }
394
395 sent = dev->netdev_ops->ndo_xdp_xmit(dev, to_send, bq->q, flags);
396 if (sent < 0) {
397 /* If ndo_xdp_xmit fails with an errno, no frames have
398 * been xmit'ed.
399 */
400 err = sent;
401 sent = 0;
402 }
403
404 /* If not all frames have been transmitted, it is our
405 * responsibility to free them
406 */
407 for (i = sent; unlikely(i < to_send); i++)
408 xdp_return_frame_rx_napi(bq->q[i]);
409
410out:
value_overwrite: Overwriting previous write to drops with value from
cnt - sent.
411 drops = cnt - sent;
412 bq->count = 0;
413 trace_xdp_devmap_xmit(bq->dev_rx, dev, sent, drops, err);
414}
drops is being calculated twice but the first value is not used. Not
sure if that was intentional or an oversight.
Colin
