On Fri, 28 Nov 2025 09:39:46 -0800, Jakub Kicinski wrote:

quoted

In zerocopy_fill_skb_from_iter(), if two copy operations are performed
and the first one succeeds while the second one fails, it returns a
failure but the count in iterator has already been decremented due to
the first successful copy. This ultimately affects the local variable
rest_len in virtio_transport_send_pkt_info(), causing the remaining
count in rest_len to be greater than the actual iterator count. As a
result, packet sending operations continue even when the iterator count
is zero, which further leads to skb->len being 0 and triggers the warning
reported by syzbot [1].

Please follow the subsystem guidelines for posting patches:
https://www.kernel.org/doc/html/next/process/maintainer-netdev.html
Your patch breaks zerocopy tests.

I see that they all timed out. I'm not familiar with this test, how can
I get more details about it?