bpf: iter_udp: Retry with a larger batch size without going back to the previous bucket

JIRA: https://issues.redhat.com/browse/RHEL-65787

commit 19ca082
Author: Martin KaFai Lau <martin.lau@kernel.org>
Date:   Fri Jan 12 11:05:28 2024 -0800

    bpf: iter_udp: Retry with a larger batch size without going back to the previous bucket

    The current logic is to use a default size 16 to batch the whole bucket.
    If it is too small, it will retry with a larger batch size.

    The current code accidentally does a state->bucket-- before retrying.
    This goes back to retry with the previous bucket which has already
    been done. This patch fixed it.

    It is hard to create a selftest. I added a WARN_ON(state->bucket < 0),
    forced a particular port to be hashed to the first bucket,
    created >16 sockets, and observed the for-loop went back
    to the "-1" bucket.

    Cc: Aditi Ghag <aditi.ghag@isovalent.com>
    Fixes: c96dac8 ("bpf: udp: Implement batching for sockets iterator")
    Acked-by: Yonghong Song <yonghong.song@linux.dev>
    Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
    Reviewed-by: Aditi Ghag <aditi.ghag@isovalent.com>
    Link: https://lore.kernel.org/r/20240112190530.3751661-2-martin.lau@linux.dev
    Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>

Author: tohojo

net/ipv4/udp.c

@@ -3256,7 +3256,6 @@ static struct sock *bpf_iter_udp_batch(struct seq_file *seq)
 		/* After allocating a larger batch, retry one more time to grab
 		 * the whole bucket.
 		 */
-		state->bucket--;
 		goto again;
 	}
 done: