[bpf-next,v2,0/2] Transfer RCU lock state across subprog calls

Message

Kumar Kartikeya Dwivedi Feb. 5, 2024, 5:56 a.m. UTC

David suggested during the discussion in [0] that we should handle RCU
locks in a similar fashion to spin locks where the verifier understands
when a lock held in a caller is released in callee, or lock taken in
callee is released in a caller, or the callee is called within a lock
critical section. This set extends the same semantics to RCU read locks
and adds a few selftests to verify correct behavior. This issue has also
come up for sched-ext programs.

This would now allow static subprog calls to be made without errors
within RCU read sections, for subprogs to release RCU locks of callers
and return to them, or for subprogs to take RCU lock which is later
released in the caller.

  [0]: https://lore.kernel.org/bpf/[e-mail]

Changelog:
----------
v1 -> v2:
v1: https://lore.kernel.org/bpf/[e-mail]

 * Add tests for global subprog behaviour (Yafang)
 * Add Acks, Tested-by (Yonghong, Yafang)

Kumar Kartikeya Dwivedi (2):
  bpf: Transfer RCU lock state between subprog calls
  selftests/bpf: Add tests for RCU lock transfer between subprogs

 kernel/bpf/verifier.c                         |   3 +-
 .../selftests/bpf/prog_tests/rcu_read_lock.c  |   6 +
 .../selftests/bpf/progs/rcu_read_lock.c       | 120 ++++++++++++++++++
 3 files changed, 127 insertions(+), 2 deletions(-)


base-commit: 2a79690eae953daaac232f93e6c5ac47ac539f2d

Comments

[e-mail] Feb. 6, 2024, 4:10 a.m. UTC | #1

Hello:

This series was applied to bpf/bpf-next.git (master)
by Alexei Starovoitov <[e-mail]>:

On Mon,  5 Feb 2024 05:56:44 +0000 you wrote:
> David suggested during the discussion in [0] that we should handle RCU
> locks in a similar fashion to spin locks where the verifier understands
> when a lock held in a caller is released in callee, or lock taken in
> callee is released in a caller, or the callee is called within a lock
> critical section. This set extends the same semantics to RCU read locks
> and adds a few selftests to verify correct behavior. This issue has also
> come up for sched-ext programs.
> 
> [...]

Here is the summary with links:
  - [bpf-next,v2,1/2] bpf: Transfer RCU lock state between subprog calls
    https://git.kernel.org/bpf/bpf-next/c/6fceea0fa59f
  - [bpf-next,v2,2/2] selftests/bpf: Add tests for RCU lock transfer between subprogs
    https://git.kernel.org/bpf/bpf-next/c/8be6a0147af3

You are awesome, thank you!