[PATCH bpf-next 0/2] bpf, sockmap: Fix udp_bpf_recvmsg() spinning on backlog-only ingress

[chenyuan_fl@163.com]

From: Yuan Chen <chenyuan@kylinos.cn>

udp_bpf_recvmsg() re-arms its receive loop on backlog-only skbs that
sk_msg_recvmsg() can never consume: whenever the backlog stays
populated, the loop re-arms on the same skb forever and recvmsg()
spins while holding the socket lock instead of sleeping.

Patch 1 aligns the re-arm condition with TCP and unix_bpf_recvmsg();
patch 2 adds a selftest that reproduces the hang.

Yuan Chen (2):
  bpf, sockmap: Fix udp_bpf_recvmsg() spinning on backlog-only ingress
  selftests/bpf: Add a test for udp_bpf_recvmsg() with a stuck backlog

 net/ipv4/udp_bpf.c                            |   2 +-
 .../bpf/prog_tests/sockmap_udp_backlog.c      | 141 ++++++++++++++++++
 .../bpf/progs/test_sockmap_udp_backlog.c      |  21 +++
 3 files changed, 163 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/sockmap_udp_backlog.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_sockmap_udp_backlog.c

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2.54.0