Both UDP and TCP socket iterators use iter->offset to track progress through a bucket, which is a measure of the number of matching sockets from the current bucket that have been seen or processed by the iterator. On subsequent iterations, if the current bucket has unprocessed items, we skip at least iter->offset matching items in the bucket before adding any remaining items to the next batch. However, iter->offset isn't always an accurate measure of "things already seen" when the underlying bucket changes between reads which can lead to repeated or skipped sockets. Instead, this series remembers the cookies of the sockets we haven't seen yet in the current bucket and resumes from the first cookie in that list that we can find on the next iteration. To be more specific, this series replaces struct sock **batch inside struct bpf_udp_iter_state with union bpf_udp_iter_batch_item *batch, where union bpf_udp_iter_batch_item can contain either a pointer to a socket or a socket cookie. During reads, batch contains pointers to all sockets in the current batch while between reads batch contains all the cookies of the sockets in the current bucket that have yet to be processed. On subsequent reads, when iteration resumes, bpf_iter_udp_batch finds the first saved cookie that matches a socket in the bucket's socket list and picks up from there to construct the next batch. On average, assuming it's rare that the next socket disappears before the next read occurs, we should only need to scan as much as we did with the offset-based approach to find the starting point. In the case that the next socket is no longer there, we keep scanning through the saved cookies list until we find a match. The worst case is when none of the sockets from last time exist anymore, but again, this should be rare. CHANGES ======= rfc [1] -> v1: * Use hlist_entry_safe directly to retrieve the first socket in the current bucket's linked list instead of immediately breaking from udp_portaddr_for_each_entry (Martin). * Cancel iteration if bpf_iter_udp_realloc_batch() can't grab enough memory to contain a full snapshot of the current bucket to prevent unwanted skips or repeats [2]. [1]: https://lore.kernel.org/bpf/20250404220221.1665428-1-jordan@xxxxxxxx/ [2]: https://lore.kernel.org/bpf/CABi4-ogUtMrH8-NVB6W8Xg_F_KDLq=yy-yu-tKr2udXE2Mu1Lg@xxxxxxxxxxxxxx/ Jordan Rife (5): bpf: udp: Use bpf_udp_iter_batch_item for bpf_udp_iter_state batch items bpf: udp: Avoid socket skips and repeats during iteration bpf: udp: Propagate ENOMEM up from bpf_iter_udp_batch selftests/bpf: Return socket cookies from sock_iter_batch progs selftests/bpf: Add tests for bucket resume logic in UDP socket iterators include/linux/udp.h | 3 + net/ipv4/udp.c | 101 +++- .../bpf/prog_tests/sock_iter_batch.c | 451 +++++++++++++++++- .../selftests/bpf/progs/bpf_tracing_net.h | 1 + .../selftests/bpf/progs/sock_iter_batch.c | 24 +- 5 files changed, 538 insertions(+), 42 deletions(-) -- 2.43.0
