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* [PATCH bpf-next v2 0/4] bpf: Add bpf_call_rcu() and bpf_call_rcu_tasks_trace()
@ 2026-09-15 11:42 Puranjay Mohan
  2026-09-15 11:42 ` [PATCH bpf-next v2 1/4] bpf: Add bpf_call_rcu() kfunc Puranjay Mohan
                   ` (4 more replies)
  0 siblings, 5 replies; 6+ messages in thread
From: Puranjay Mohan @ 2026-09-15 11:42 UTC (permalink / raw)
  To: bpf, rcu
  Cc: Puranjay Mohan, Alexei Starovoitov, Daniel Borkmann,
	Andrii Nakryiko, Martin KaFai Lau, Eduard Zingerman,
	Kumar Kartikeya Dwivedi, Song Liu, Yonghong Song,
	Harry Yoo (Oracle), Paul E. McKenney

Changelog:
v1: https://lore.kernel.org/all/20260907134552.1772405-1-puranjay@kernel.org/
Changes in v2:
- Rebase on bpf-next/master
- Use rcu_read_lock_dont_migrate() over open coding (Alexei)
- Improve re-arming selftest to detect failure (Sashiko)

BPF programs that manage their own objects have no way to run their own
logic once an RCU grace period has elapsed.  bpf_obj_drop() defers a
free, but returning an index to an allocator or unpinning a resource
once readers are done has no equivalent.  sched_ext's BPF library works
around this today by pushing freed nodes onto a list and having a
userspace thread call membarrier(MEMBARRIER_CMD_GLOBAL) and then run a
BPF program to reclaim them; it is the first intended user.

Add:

	int bpf_call_rcu(struct bpf_rcu_head *rh, void *map,
			 int (*callback)(struct bpf_map *map, void *key,
					 void *value));

and bpf_call_rcu_tasks_trace(), same signature, which also waits for
sleepable programs.

@rh is a struct bpf_rcu_head embedded in a value of @map, so the
callback runs as callback(map, key, value) for the element it lives in
and needs no cookie.  The field is only accepted in BPF_MAP_TYPE_ARRAY,
and arming holds a reference on the calling program until the callback
has run.  Patch 1 covers the lifetime rules.

This needs

  https://lore.kernel.org/all/20260810122758.183765-1-puranjay@kernel.org/

for call_rcu() and call_srcu() to be safe from the contexts a BPF
program can be called in.

Puranjay Mohan (4):
  bpf: Add bpf_call_rcu() kfunc
  selftests/bpf: Add tests for bpf_call_rcu()
  bpf: Add bpf_call_rcu_tasks_trace() kfunc
  selftests/bpf: Add a test for bpf_call_rcu_tasks_trace()

 include/linux/bpf.h                           |  10 +
 include/uapi/linux/bpf.h                      |   4 +
 kernel/bpf/btf.c                              |   7 +
 kernel/bpf/helpers.c                          | 102 +++++++++
 kernel/bpf/map_in_map.c                       |   4 +
 kernel/bpf/map_iter.c                         |   6 +
 kernel/bpf/syscall.c                          |  11 +-
 kernel/bpf/verifier.c                         |  84 ++++++-
 tools/include/uapi/linux/bpf.h                |   4 +
 .../selftests/bpf/prog_tests/call_rcu.c       | 216 ++++++++++++++++++
 tools/testing/selftests/bpf/progs/call_rcu.c  |  89 ++++++++
 .../selftests/bpf/progs/call_rcu_fail.c       | 114 +++++++++
 12 files changed, 648 insertions(+), 3 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/call_rcu.c
 create mode 100644 tools/testing/selftests/bpf/progs/call_rcu.c
 create mode 100644 tools/testing/selftests/bpf/progs/call_rcu_fail.c


base-commit: 5ef40d69b38a93bc9951dadb1a15c85c597e1a40
-- 
2.53.0-Meta


^ permalink raw reply	[flat|nested] 6+ messages in thread
end of thread, other threads:[~2026-09-15 12:09 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz follow: Atom feed
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2026-09-15 11:42 [PATCH bpf-next v2 0/4] bpf: Add bpf_call_rcu() and bpf_call_rcu_tasks_trace() Puranjay Mohan
2026-09-15 11:42 ` [PATCH bpf-next v2 1/4] bpf: Add bpf_call_rcu() kfunc Puranjay Mohan
2026-09-15 11:42 ` [PATCH bpf-next v2 2/4] selftests/bpf: Add tests for bpf_call_rcu() Puranjay Mohan
2026-09-15 11:42 ` [PATCH bpf-next v2 3/4] bpf: Add bpf_call_rcu_tasks_trace() kfunc Puranjay Mohan
2026-09-15 11:42 ` [PATCH bpf-next v2 4/4] selftests/bpf: Add a test for bpf_call_rcu_tasks_trace() Puranjay Mohan
2026-09-15 12:09 ` [PATCH bpf-next v2 0/4] bpf: Add bpf_call_rcu() and bpf_call_rcu_tasks_trace() Puranjay Mohan

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