Commit 635599ba authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Alexei Starovoitov
Browse files

selftests/bpf: Sync RCU before unloading bpf_testmod 



If some of the subtests use module BTFs through ksyms, they will cause
bpf_prog to take a refcount on bpf_testmod module, which will prevent it from
successfully unloading. Module's refcnt is decremented when bpf_prog is freed,
which generally happens in RCU callback. So we need to trigger
syncronize_rcu() in the kernel, which can be achieved nicely with
membarrier(MEMBARRIER_CMD_SHARED) or membarrier(MEMBARRIER_CMD_GLOBAL) syscall.
So do that in kernel_sync_rcu() and make it available to other test inside the
test_progs. This synchronize_rcu() is called before attempting to unload
bpf_testmod.

Fixes: 9f7fa225 ("selftests/bpf: Add bpf_testmod kernel module for testing")
Suggested-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarYonghong Song <yhs@fb.com>
Acked-by: default avatarHao Luo <haoluo@google.com>
Link: https://lore.kernel.org/bpf/20210112075520.4103414-5-andrii@kernel.org
parent 936f8946

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

+0 −33
Original line number Diff line number Diff line
@@ -20,39 +20,6 @@ static __u32 bpf_map_id(struct bpf_map *map) 
	return info.id;

}



/*

 * Trigger synchronize_rcu() in kernel.

 *

 * ARRAY_OF_MAPS/HASH_OF_MAPS lookup/update operations trigger synchronize_rcu()

 * if looking up an existing non-NULL element or updating the map with a valid

 * inner map FD. Use this fact to trigger synchronize_rcu(): create map-in-map,

 * create a trivial ARRAY map, update map-in-map with ARRAY inner map. Then

 * cleanup. At the end, at least one synchronize_rcu() would be called.

 */

static int kern_sync_rcu(void)

{

	int inner_map_fd, outer_map_fd, err, zero = 0;



	inner_map_fd = bpf_create_map(BPF_MAP_TYPE_ARRAY, 4, 4, 1, 0);

	if (CHECK(inner_map_fd < 0, "inner_map_create", "failed %d\n", -errno))

		return -1;



	outer_map_fd = bpf_create_map_in_map(BPF_MAP_TYPE_ARRAY_OF_MAPS, NULL,

					     sizeof(int), inner_map_fd, 1, 0);

	if (CHECK(outer_map_fd < 0, "outer_map_create", "failed %d\n", -errno)) {

		close(inner_map_fd);

		return -1;

	}



	err = bpf_map_update_elem(outer_map_fd, &zero, &inner_map_fd, 0);

	if (err)

		err = -errno;

	CHECK(err, "outer_map_update", "failed %d\n", err);

	close(inner_map_fd);

	close(outer_map_fd);

	return err;

}



static void test_lookup_update(void)

{

	int map1_fd, map2_fd, map3_fd, map4_fd, map5_fd, map1_id, map2_id;

tools/testing/selftests/bpf/test_progs.c

+11 −0
Original line number Diff line number Diff line
@@ -11,6 +11,7 @@ 
#include <signal.h>

#include <string.h>

#include <execinfo.h> /* backtrace */

#include <linux/membarrier.h>



#define EXIT_NO_TEST		2

#define EXIT_ERR_SETUP_INFRA	3
@@ -370,8 +371,18 @@ static int delete_module(const char *name, int flags) 
	return syscall(__NR_delete_module, name, flags);

}



/*

 * Trigger synchronize_rcu() in kernel.

 */

int kern_sync_rcu(void)

{

	return syscall(__NR_membarrier, MEMBARRIER_CMD_SHARED, 0, 0);

}



static void unload_bpf_testmod(void)

{

	if (kern_sync_rcu())

		fprintf(env.stderr, "Failed to trigger kernel-side RCU sync!\n");

	if (delete_module("bpf_testmod", 0)) {

		if (errno == ENOENT) {

			if (env.verbosity > VERBOSE_NONE)

tools/testing/selftests/bpf/test_progs.h

+1 −0
Original line number Diff line number Diff line
@@ -219,6 +219,7 @@ int bpf_find_map(const char *test, struct bpf_object *obj, const char *name); 
int compare_map_keys(int map1_fd, int map2_fd);

int compare_stack_ips(int smap_fd, int amap_fd, int stack_trace_len);

int extract_build_id(char *build_id, size_t size);

int kern_sync_rcu(void);



#ifdef __x86_64__

#define SYS_NANOSLEEP_KPROBE_NAME "__x64_sys_nanosleep"