Commit 2d92ef7d authored by Alexei Starovoitov's avatar Alexei Starovoitov
Browse files

Merge branch 'selftests-bpf-introduce-experimental-bpf_in_interrupt' 

Leon Hwang says:

====================
selftests/bpf: Introduce experimental bpf_in_interrupt()

Filtering pid_tgid is meanlingless when the current task is preempted by
an interrupt.

To address this, introduce 'bpf_in_interrupt()' helper function, which
allows BPF programs to determine whether they are executing in interrupt
context.

'get_preempt_count()':

* On x86, '*(int *) bpf_this_cpu_ptr(&__preempt_count)'.
* On arm64, 'bpf_get_current_task_btf()->thread_info.preempt.count'.

Then 'bpf_in_interrupt()' will be:

* If !PREEMPT_RT, 'get_preempt_count() & (NMI_MASK | HARDIRQ_MASK
  | SOFTIRQ_MASK)'.
* If PREEMPT_RT, '(get_preempt_count() & (NMI_MASK | HARDIRQ_MASK))
  | (bpf_get_current_task_btf()->softirq_disable_cnt & SOFTIRQ_MASK)'.

'bpf_in_interrupt()' runs well when PREEMPT_RT is enabled. But it's
difficult for me to test it well because I'm not familiar with
PREEMPT_RT.

Changes:
v2 -> v3:
* Address comments from Alexei:
  * Move bpf_in_interrupt() to bpf_experimental.h.
  * Add support for arm64.
v2: https://lore.kernel.org/bpf/20250825131502.54269-1-leon.hwang@linux.dev/

v1 -> v2:
* Fix a build error reported by test bot.
====================

Link: https://patch.msgid.link/20250903140438.59517-1-leon.hwang@linux.dev


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parents 929adf88 88a3bde4

tools/testing/selftests/bpf/bpf_experimental.h

+54 −0
Original line number Diff line number Diff line
@@ -599,4 +599,58 @@ extern void bpf_iter_dmabuf_destroy(struct bpf_iter_dmabuf *it) __weak __ksym; 
extern int bpf_cgroup_read_xattr(struct cgroup *cgroup, const char *name__str,

				 struct bpf_dynptr *value_p) __weak __ksym;



#define PREEMPT_BITS	8

#define SOFTIRQ_BITS	8

#define HARDIRQ_BITS	4

#define NMI_BITS	4



#define PREEMPT_SHIFT	0

#define SOFTIRQ_SHIFT	(PREEMPT_SHIFT + PREEMPT_BITS)

#define HARDIRQ_SHIFT	(SOFTIRQ_SHIFT + SOFTIRQ_BITS)

#define NMI_SHIFT	(HARDIRQ_SHIFT + HARDIRQ_BITS)



#define __IRQ_MASK(x)	((1UL << (x))-1)



#define SOFTIRQ_MASK	(__IRQ_MASK(SOFTIRQ_BITS) << SOFTIRQ_SHIFT)

#define HARDIRQ_MASK	(__IRQ_MASK(HARDIRQ_BITS) << HARDIRQ_SHIFT)

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



extern bool CONFIG_PREEMPT_RT __kconfig __weak;

#ifdef bpf_target_x86

extern const int __preempt_count __ksym;

#endif



struct task_struct___preempt_rt {

	int softirq_disable_cnt;

} __attribute__((preserve_access_index));



static inline int get_preempt_count(void)

{

#if defined(bpf_target_x86)

	return *(int *) bpf_this_cpu_ptr(&__preempt_count);

#elif defined(bpf_target_arm64)

	return bpf_get_current_task_btf()->thread_info.preempt.count;

#endif

	return 0;

}



/* Description

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

 *	* x86

 *	* arm64

 */

static inline int bpf_in_interrupt(void)

{

	struct task_struct___preempt_rt *tsk;

	int pcnt;



	pcnt = get_preempt_count();

	if (!CONFIG_PREEMPT_RT)

		return pcnt & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_MASK);



	tsk = (void *) bpf_get_current_task_btf();

	return (pcnt & (NMI_MASK | HARDIRQ_MASK)) |

	       (tsk->softirq_disable_cnt & SOFTIRQ_MASK);

}



#endif

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

+30 −0
Original line number Diff line number Diff line
@@ -3,6 +3,7 @@ 
#include <test_progs.h>

#include "timer.skel.h"

#include "timer_failure.skel.h"

#include "timer_interrupt.skel.h"



#define NUM_THR 8
@@ -95,3 +96,32 @@ void serial_test_timer(void) 


	RUN_TESTS(timer_failure);

}



void test_timer_interrupt(void)

{

	struct timer_interrupt *skel = NULL;

	int err, prog_fd;

	LIBBPF_OPTS(bpf_test_run_opts, opts);



	skel = timer_interrupt__open_and_load();

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

		return;



	err = timer_interrupt__attach(skel);

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

		goto out;



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

	err = bpf_prog_test_run_opts(prog_fd, &opts);

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

		goto out;



	usleep(50);



	ASSERT_EQ(skel->bss->in_interrupt, 0, "in_interrupt");

	if (skel->bss->preempt_count)

		ASSERT_NEQ(skel->bss->in_interrupt_cb, 0, "in_interrupt_cb");



out:

	timer_interrupt__destroy(skel);

}

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

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

#include <vmlinux.h>

#include <bpf/bpf_helpers.h>

#include <bpf/bpf_tracing.h>

#include "bpf_experimental.h"



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



#define CLOCK_MONOTONIC		1



int preempt_count;

int in_interrupt;

int in_interrupt_cb;



struct elem {

	struct bpf_timer t;

};



struct {

	__uint(type, BPF_MAP_TYPE_ARRAY);

	__uint(max_entries, 1);

	__type(key, int);

	__type(value, struct elem);

} array SEC(".maps");



static int timer_in_interrupt(void *map, int *key, struct bpf_timer *timer)

{

	preempt_count = get_preempt_count();

	in_interrupt_cb = bpf_in_interrupt();

	return 0;

}



SEC("fentry/bpf_fentry_test1")

int BPF_PROG(test_timer_interrupt)

{

	struct bpf_timer *timer;

	int key = 0;



	timer = bpf_map_lookup_elem(&array, &key);

	if (!timer)

		return 0;



	in_interrupt = bpf_in_interrupt();

	bpf_timer_init(timer, &array, CLOCK_MONOTONIC);

	bpf_timer_set_callback(timer, timer_in_interrupt);

	bpf_timer_start(timer, 0, 0);

	return 0;

}