[PATCH bpf 0/6] libbpf: Fix ring buffer consumption

[Tamir Duberstein <tamird@kernel.org>]

Fix several correctness issues in libbpf's ring buffer consumer.

A zero record bound currently consumes one record. A NULL callback is
accepted during manager construction but crashes when callback-based
consumption reaches the ring. Position counters stop consumption after
wrapping because they are compared by magnitude.

The consumer can also miss a readiness notification after publishing its
position and checking for new data without a full StoreLoad barrier. Use
compiler atomics and add the missing barrier, including when retrying a
busy record after publishing earlier records.

Callback traversal does not follow the overwrite position maintained by
BPF_F_RB_OVERWRITE maps. Reject callback consumption of those maps, as
discussed here:
https://lore.kernel.org/bpf/CAEf4Bzaq5drHWChXoRBnrmkb6reAsSVj8r=uByFSup31FMA7hw@mail.gmail.com/

Andrew Werner found the position-wrap and missed-wakeup failures while
implementing Aya's ring buffer reader. Aya's original implementation
contains the equality reasoning and edge-triggered regression test:
https://github.com/aya-rs/aya/commit/e2cf734490bc188bcedb1eac92d23d81123e42cd

Aya later corrected the consumer ordering with the same explicit fence:
https://github.com/aya-rs/aya/commit/7277a57ea8cdb74918d3096a4b22b6d814481973

Assisted-by: Codex:gpt-5.5
Signed-off-by: Tamir Duberstein <tamird@kernel.org>
---
Tamir Duberstein (6):
      libbpf: ringbuf: Honor zero consume bounds
      libbpf: ringbuf: Prevent NULL callback crash
      libbpf: ringbuf: Handle position counter wrap
      libbpf: ringbuf: Use compiler atomics
      libbpf: ringbuf: Prevent missed wakeups
      libbpf: ringbuf: Reject overwrite callback use

 tools/lib/bpf/libbpf.h                           |  34 +++-
 tools/lib/bpf/ringbuf.c                          |  84 +++++++--
 tools/testing/selftests/bpf/prog_tests/ringbuf.c | 229 +++++++++++++++++++++++
 3 files changed, 323 insertions(+), 24 deletions(-)
---
base-commit: e7ae89a0c97ce2b68b0983cd01eda67cf373517d
change-id: 20260613-bpf-ringbuf-fixes-e9a8b3c6125b

Best regards,
--  
Tamir Duberstein <tamird@kernel.org>