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selftests/bpf: Tracing prog can still do lookup under busy lock

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This patch modifies the task_ls_recursion test to check that
the first bpf_task_storage_get(&map_a, ...) in BPF_PROG(on_update)
can still do the lockless lookup even it cannot acquire the percpu
busy lock.  If the lookup succeeds, it will increment the value
by 1 and the value in the task storage map_a will become 200+1=201.
After that, BPF_PROG(on_update) tries to delete from map_a and
should get -EBUSY because it cannot acquire the percpu busy lock
after finding the data.

Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://lore.kernel.org/r/20221025184524.3526117-10-martin.lau@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Martin KaFai Lau 2022-10-25 11:45:24 -07:00 committed by Alexei Starovoitov
parent 0334b4d882
commit 387b532138
2 changed files with 87 additions and 6 deletions
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48
tools/testing/selftests/bpf/prog_tests/task_local_storage.c
View file

@ -8,6 +8,7 @@
#include <sys/syscall.h> /* For SYS_xxx definitions */
#include <sys/types.h>
#include <test_progs.h>
#include "task_local_storage_helpers.h"
#include "task_local_storage.skel.h"
#include "task_local_storage_exit_creds.skel.h"
#include "task_ls_recursion.skel.h"
@ -78,21 +79,64 @@ static void test_exit_creds(void)
static void test_recursion(void)
{
int err, map_fd, prog_fd, task_fd;
struct task_ls_recursion *skel;
int err;
struct bpf_prog_info info;
__u32 info_len = sizeof(info);
long value;
task_fd = sys_pidfd_open(getpid(), 0);
if (!ASSERT_NEQ(task_fd, -1, "sys_pidfd_open"))
return;
skel = task_ls_recursion__open_and_load();
if (!ASSERT_OK_PTR(skel, "skel_open_and_load"))
return;
goto out;
err = task_ls_recursion__attach(skel);
if (!ASSERT_OK(err, "skel_attach"))
goto out;
/* trigger sys_enter, make sure it does not cause deadlock */
skel->bss->test_pid = getpid();
syscall(SYS_gettid);
skel->bss->test_pid = 0;
task_ls_recursion__detach(skel);
/* Refer to the comment in BPF_PROG(on_update) for
* the explanation on the value 201 and 100.
*/
map_fd = bpf_map__fd(skel->maps.map_a);
err = bpf_map_lookup_elem(map_fd, &task_fd, &value);
ASSERT_OK(err, "lookup map_a");
ASSERT_EQ(value, 201, "map_a value");
ASSERT_EQ(skel->bss->nr_del_errs, 1, "bpf_task_storage_delete busy");
map_fd = bpf_map__fd(skel->maps.map_b);
err = bpf_map_lookup_elem(map_fd, &task_fd, &value);
ASSERT_OK(err, "lookup map_b");
ASSERT_EQ(value, 100, "map_b value");
prog_fd = bpf_program__fd(skel->progs.on_lookup);
memset(&info, 0, sizeof(info));
err = bpf_obj_get_info_by_fd(prog_fd, &info, &info_len);
ASSERT_OK(err, "get prog info");
ASSERT_GT(info.recursion_misses, 0, "on_lookup prog recursion");
prog_fd = bpf_program__fd(skel->progs.on_update);
memset(&info, 0, sizeof(info));
err = bpf_obj_get_info_by_fd(prog_fd, &info, &info_len);
ASSERT_OK(err, "get prog info");
ASSERT_EQ(info.recursion_misses, 0, "on_update prog recursion");
prog_fd = bpf_program__fd(skel->progs.on_enter);
memset(&info, 0, sizeof(info));
err = bpf_obj_get_info_by_fd(prog_fd, &info, &info_len);
ASSERT_OK(err, "get prog info");
ASSERT_EQ(info.recursion_misses, 0, "on_enter prog recursion");
out:
close(task_fd);
task_ls_recursion__destroy(skel);
}

45
tools/testing/selftests/bpf/progs/task_ls_recursion.c
View file

@ -5,7 +5,13 @@
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_tracing.h>
#ifndef EBUSY
#define EBUSY 16
#endif
char _license[] SEC("license") = "GPL";
int nr_del_errs = 0;
int test_pid = 0;
struct {
__uint(type, BPF_MAP_TYPE_TASK_STORAGE);
@ -26,6 +32,13 @@ int BPF_PROG(on_lookup)
{
struct task_struct *task = bpf_get_current_task_btf();
if (!test_pid || task->pid != test_pid)
return 0;
/* The bpf_task_storage_delete will call
* bpf_local_storage_lookup. The prog->active will
* stop the recursion.
*/
bpf_task_storage_delete(&map_a, task);
bpf_task_storage_delete(&map_b, task);
return 0;
@ -37,11 +50,32 @@ int BPF_PROG(on_update)
struct task_struct *task = bpf_get_current_task_btf();
long *ptr;
if (!test_pid || task->pid != test_pid)
return 0;
ptr = bpf_task_storage_get(&map_a, task, 0,
BPF_LOCAL_STORAGE_GET_F_CREATE);
if (ptr)
*ptr += 1;
/* ptr will not be NULL when it is called from
* the bpf_task_storage_get(&map_b,...F_CREATE) in
* the BPF_PROG(on_enter) below. It is because
* the value can be found in map_a and the kernel
* does not need to acquire any spin_lock.
*/
if (ptr) {
int err;
*ptr += 1;
err = bpf_task_storage_delete(&map_a, task);
if (err == -EBUSY)
nr_del_errs++;
}
/* This will still fail because map_b is empty and
* this BPF_PROG(on_update) has failed to acquire
* the percpu busy lock => meaning potential
* deadlock is detected and it will fail to create
* new storage.
*/
ptr = bpf_task_storage_get(&map_b, task, 0,
BPF_LOCAL_STORAGE_GET_F_CREATE);
if (ptr)
@ -57,14 +91,17 @@ int BPF_PROG(on_enter, struct pt_regs *regs, long id)
long *ptr;
task = bpf_get_current_task_btf();
if (!test_pid || task->pid != test_pid)
return 0;
ptr = bpf_task_storage_get(&map_a, task, 0,
BPF_LOCAL_STORAGE_GET_F_CREATE);
if (ptr)
if (ptr && !*ptr)
*ptr = 200;
ptr = bpf_task_storage_get(&map_b, task, 0,
BPF_LOCAL_STORAGE_GET_F_CREATE);
if (ptr)
if (ptr && !*ptr)
*ptr = 100;
return 0;
}