[bpf-next,v1,0/2] Enable static subprog calls in spin lock critical sections

Message

Kumar Kartikeya Dwivedi Feb. 4, 2024, 12:02 p.m. UTC

This set allows a BPF program to make a call to a static subprog within
a bpf_spin_lock critical section. This problem has been hit in sched-ext
and ghOSt [0] as well, and is mostly an annoyance which is worked around
by inling the static subprog into the critical section.

In case of sched-ext, there are a lot of other helper/kfunc calls that
need to be allow listed for the support to be complete, but a separate
follow up will deal with that.

Unlike static subprogs, global subprogs cannot be allowed yet as the
verifier will not explore their body when encountering a call
instruction for them. Therefore, we would need an alternative approach
(some sort of function summarization to ensure a lock is never taken
from a global subprog and all its callees).

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

Kumar Kartikeya Dwivedi (2):
  bpf: Allow calling static subprogs while holding a bpf_spin_lock
  selftests/bpf: Add test for static subprog call in lock cs

 kernel/bpf/verifier.c                         | 10 ++-
 .../selftests/bpf/prog_tests/spin_lock.c      |  2 +
 .../selftests/bpf/progs/test_spin_lock.c      | 65 +++++++++++++++++++
 .../selftests/bpf/progs/test_spin_lock_fail.c | 44 +++++++++++++
 .../selftests/bpf/progs/verifier_spin_lock.c  |  2 +-
 5 files changed, 119 insertions(+), 4 deletions(-)


base-commit: 2a79690eae953daaac232f93e6c5ac47ac539f2d