Merge branch 'selftests-bpf-introduce-execution-context-detection-helpers'

Changwoo Min says:

====================
selftests/bpf: Introduce execution context detection helpers

This series introduces four new BPF-native inline helpers -- bpf_in_nmi(),
bpf_in_hardirq(), bpf_in_serving_softirq(), and bpf_in_task() -- to allow
BPF programs to query the current execution context.

Following the feedback on v1, these are implemented in bpf_experimental.h
as inline helpers wrapping get_preempt_count(). This approach allows the
logic to be JIT-inlined for better performance compared to a kfunc call,
while providing the granular context detection (e.g., hardirq vs. softirq)
required by subsystems like sched_ext.

The series includes a new selftest suite, exe_ctx, which uses bpf_testmod
to verify context detection across Task, HardIRQ, and SoftIRQ boundaries
via irq_work and tasklets. NMI context testing is omitted as NMIs cannot
be triggered deterministically within software-only BPF CI environments.

ChangeLog v2 -> v3:
- Added exe_ctx to DENYLIST.s390x since new helpers are supported only
  on x86 and arm64 (patch 2).
- Added comments to helpers describing supported architectures (patch 1).

ChangeLog v1 -> v2:
- Dropped the core kernel kfunc implementations, and implemented context
  detection as inline BPF helpers in bpf_experimental.h.
- Renamed the selftest suite from ctx_kfunc to exe_ctx to reflect the
  change from kfuncs to helpers.
- Updated BPF programs to use the new inline helpers.
- Swapped clean-up order between tasklet and irqwork in bpf_testmod to
  avoid re-scheduling the already-killed tasklet (reported by bot+bpf-ci).
====================

Link: https://patch.msgid.link/20260125115413.117502-1-changwoo@igalia.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

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