Commit 59ef78d4 authored by Alexei Starovoitov's avatar Alexei Starovoitov
Browse files

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: default avatarAlexei Starovoitov <ast@kernel.org>
parents c390adfd 221b5e76

tools/testing/selftests/bpf/DENYLIST.s390x

+1 −0
Original line number Diff line number Diff line 
# TEMPORARY

# Alphabetical order

exe_ctx                                  # execution context check (e.g., hardirq, softirq, etc)

get_stack_raw_tp                         # user_stack corrupted user stack                                             (no backchain userspace)

stacktrace_build_id                      # compare_map_keys stackid_hmap vs. stackmap err -2 errno 2                   (?)

tools/testing/selftests/bpf/bpf_experimental.h

+58 −0
Original line number Diff line number Diff line
@@ -610,6 +610,8 @@ extern int bpf_cgroup_read_xattr(struct cgroup *cgroup, const char *name__str, 
#define HARDIRQ_MASK	(__IRQ_MASK(HARDIRQ_BITS) << HARDIRQ_SHIFT)

#define NMI_MASK	(__IRQ_MASK(NMI_BITS)     << NMI_SHIFT)



#define SOFTIRQ_OFFSET	(1UL << SOFTIRQ_SHIFT)



extern bool CONFIG_PREEMPT_RT __kconfig __weak;

#ifdef bpf_target_x86

extern const int __preempt_count __ksym;
@@ -648,4 +650,60 @@ static inline int bpf_in_interrupt(void) 
	       (tsk->softirq_disable_cnt & SOFTIRQ_MASK);

}



/* Description

 *	Report whether it is in NMI context. Only works on the following archs:

 *	* x86

 *	* arm64

 */

static inline int bpf_in_nmi(void)

{

	return get_preempt_count() & NMI_MASK;

}



/* Description

 *	Report whether it is in hard IRQ context. Only works on the following archs:

 *	* x86

 *	* arm64

 */

static inline int bpf_in_hardirq(void)

{

	return get_preempt_count() & HARDIRQ_MASK;

}



/* Description

 *	Report whether it is in softirq context. Only works on the following archs:

 *	* x86

 *	* arm64

 */

static inline int bpf_in_serving_softirq(void)

{

	struct task_struct___preempt_rt *tsk;

	int pcnt;



	pcnt = get_preempt_count();

	if (!CONFIG_PREEMPT_RT)

		return (pcnt & SOFTIRQ_MASK) & SOFTIRQ_OFFSET;



	tsk = (void *) bpf_get_current_task_btf();

	return (tsk->softirq_disable_cnt & SOFTIRQ_MASK) & SOFTIRQ_OFFSET;

}



/* Description

 *	Report whether it is in task context. Only works on the following archs:

 *	* x86

 *	* arm64

 */

static inline int bpf_in_task(void)

{

	struct task_struct___preempt_rt *tsk;

	int pcnt;



	pcnt = get_preempt_count();

	if (!CONFIG_PREEMPT_RT)

		return !(pcnt & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET));



	tsk = (void *) bpf_get_current_task_btf();

	return !((pcnt & (NMI_MASK | HARDIRQ_MASK)) |

		 ((tsk->softirq_disable_cnt & SOFTIRQ_MASK) & SOFTIRQ_OFFSET));

}

#endif

tools/testing/selftests/bpf/prog_tests/exe_ctx.c

0 → 100644
+59 −0
Original line number Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0

/*

 * Copyright (c) 2026 Valve Corporation.

 * Author: Changwoo Min <changwoo@igalia.com>

 */



#include <test_progs.h>

#include <sys/syscall.h>

#include "test_ctx.skel.h"



void test_exe_ctx(void)

{

	LIBBPF_OPTS(bpf_test_run_opts, opts);

	cpu_set_t old_cpuset, target_cpuset;

	struct test_ctx *skel;

	int err, prog_fd;



	/* 1. Pin the current process to CPU 0. */

	if (sched_getaffinity(0, sizeof(old_cpuset), &old_cpuset) == 0) {

		CPU_ZERO(&target_cpuset);

		CPU_SET(0, &target_cpuset);

		ASSERT_OK(sched_setaffinity(0, sizeof(target_cpuset),

					    &target_cpuset), "setaffinity");

	}



	skel = test_ctx__open_and_load();

	if (!ASSERT_OK_PTR(skel, "skel_load"))

		goto restore_affinity;



	err = test_ctx__attach(skel);

	if (!ASSERT_OK(err, "skel_attach"))

		goto cleanup;



	/* 2. When we run this, the kernel will execute the BPF prog on CPU 0. */

	prog_fd = bpf_program__fd(skel->progs.trigger_all_contexts);

	err = bpf_prog_test_run_opts(prog_fd, &opts);

	ASSERT_OK(err, "test_run_trigger");



	/* 3. Wait for the local CPU's softirq/tasklet to finish. */

	for (int i = 0; i < 1000; i++) {

		if (skel->bss->count_task > 0 &&

		    skel->bss->count_hardirq > 0 &&

		    skel->bss->count_softirq > 0)

			break;

		usleep(1000); /* Wait 1ms per iteration, up to 1 sec total */

	}



	/* On CPU 0, these should now all be non-zero. */

	ASSERT_GT(skel->bss->count_task, 0, "task_ok");

	ASSERT_GT(skel->bss->count_hardirq, 0, "hardirq_ok");

	ASSERT_GT(skel->bss->count_softirq, 0, "softirq_ok");



cleanup:

	test_ctx__destroy(skel);



restore_affinity:

	ASSERT_OK(sched_setaffinity(0, sizeof(old_cpuset), &old_cpuset),

		  "restore_affinity");

}

tools/testing/selftests/bpf/progs/test_ctx.c

0 → 100644
+48 −0
Original line number Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0

/*

 * Copyright (c) 2026 Valve Corporation.

 * Author: Changwoo Min <changwoo@igalia.com>

 */



#include "vmlinux.h"

#include <bpf/bpf_helpers.h>

#include <bpf/bpf_tracing.h>

#include "bpf_experimental.h"



char _license[] SEC("license") = "GPL";



extern void bpf_kfunc_trigger_ctx_check(void) __ksym;



int count_hardirq;

int count_softirq;

int count_task;



/* Triggered via bpf_prog_test_run from user-space */

SEC("syscall")

int trigger_all_contexts(void *ctx)

{

	if (bpf_in_task())

		__sync_fetch_and_add(&count_task, 1);



	/* Trigger the firing of a hardirq and softirq for test. */

	bpf_kfunc_trigger_ctx_check();

	return 0;

}



/* Observer for HardIRQ */

SEC("fentry/bpf_testmod_test_hardirq_fn")

int BPF_PROG(on_hardirq)

{

	if (bpf_in_hardirq())

		__sync_fetch_and_add(&count_hardirq, 1);

	return 0;

}



/* Observer for SoftIRQ */

SEC("fentry/bpf_testmod_test_softirq_fn")

int BPF_PROG(on_softirq)

{

	if (bpf_in_serving_softirq())

		__sync_fetch_and_add(&count_softirq, 1);

	return 0;

}

tools/testing/selftests/bpf/test_kmods/bpf_testmod.c

+32 −0
Original line number Diff line number Diff line
@@ -1168,6 +1168,33 @@ __bpf_kfunc int bpf_kfunc_implicit_arg(int a, struct bpf_prog_aux *aux); 
__bpf_kfunc int bpf_kfunc_implicit_arg_legacy(int a, int b, struct bpf_prog_aux *aux);

__bpf_kfunc int bpf_kfunc_implicit_arg_legacy_impl(int a, int b, struct bpf_prog_aux *aux);



/* hook targets */

noinline void bpf_testmod_test_hardirq_fn(void) { barrier(); }

noinline void bpf_testmod_test_softirq_fn(void) { barrier(); }



/* Tasklet for SoftIRQ context */

static void ctx_check_tasklet_fn(struct tasklet_struct *t)

{

	bpf_testmod_test_softirq_fn();

}



DECLARE_TASKLET(ctx_check_tasklet, ctx_check_tasklet_fn);



/* IRQ Work for HardIRQ context */

static void ctx_check_irq_fn(struct irq_work *work)

{

	bpf_testmod_test_hardirq_fn();

	tasklet_schedule(&ctx_check_tasklet);

}



static struct irq_work ctx_check_irq = IRQ_WORK_INIT_HARD(ctx_check_irq_fn);



/* The kfunc trigger */

__bpf_kfunc void bpf_kfunc_trigger_ctx_check(void)

{

	irq_work_queue(&ctx_check_irq);

}



BTF_KFUNCS_START(bpf_testmod_check_kfunc_ids)

BTF_ID_FLAGS(func, bpf_testmod_test_mod_kfunc)

BTF_ID_FLAGS(func, bpf_kfunc_call_test1)
@@ -1213,6 +1240,7 @@ BTF_ID_FLAGS(func, bpf_kfunc_multi_st_ops_test_1_assoc, KF_IMPLICIT_ARGS) 
BTF_ID_FLAGS(func, bpf_kfunc_implicit_arg, KF_IMPLICIT_ARGS)

BTF_ID_FLAGS(func, bpf_kfunc_implicit_arg_legacy, KF_IMPLICIT_ARGS)

BTF_ID_FLAGS(func, bpf_kfunc_implicit_arg_legacy_impl)

BTF_ID_FLAGS(func, bpf_kfunc_trigger_ctx_check)

BTF_KFUNCS_END(bpf_testmod_check_kfunc_ids)



static int bpf_testmod_ops_init(struct btf *btf)
@@ -1844,6 +1872,10 @@ static void bpf_testmod_exit(void) 
	while (refcount_read(&prog_test_struct.cnt) > 1)

		msleep(20);



	/* Clean up irqwork and tasklet */

	irq_work_sync(&ctx_check_irq);

	tasklet_kill(&ctx_check_tasklet);



	bpf_kfunc_close_sock();

	sysfs_remove_bin_file(kernel_kobj, &bin_attr_bpf_testmod_file);

	unregister_bpf_testmod_uprobe();