From 387b532138eed5b12e1afa68cafb6a389507310f Mon Sep 17 00:00:00 2001 From: Martin KaFai Lau Date: Tue, 25 Oct 2022 11:45:24 -0700 Subject: [PATCH] selftests/bpf: Tracing prog can still do lookup under busy lock 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 Link: https://lore.kernel.org/r/20221025184524.3526117-10-martin.lau@linux.dev Signed-off-by: Alexei Starovoitov --- .../selftests/bpf/prog_tests/task_local_storage.c | 48 +++++++++++++++++++++- .../selftests/bpf/progs/task_ls_recursion.c | 43 +++++++++++++++++-- 2 files changed, 86 insertions(+), 5 deletions(-) diff --git a/tools/testing/selftests/bpf/prog_tests/task_local_storage.c b/tools/testing/selftests/bpf/prog_tests/task_local_storage.c index ae535f5..a176bd7 100644 --- a/tools/testing/selftests/bpf/prog_tests/task_local_storage.c +++ b/tools/testing/selftests/bpf/prog_tests/task_local_storage.c @@ -8,6 +8,7 @@ #include /* For SYS_xxx definitions */ #include #include +#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 @@ out: 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); } diff --git a/tools/testing/selftests/bpf/progs/task_ls_recursion.c b/tools/testing/selftests/bpf/progs/task_ls_recursion.c index 564583d..4542dc6 100644 --- a/tools/testing/selftests/bpf/progs/task_ls_recursion.c +++ b/tools/testing/selftests/bpf/progs/task_ls_recursion.c @@ -5,7 +5,13 @@ #include #include +#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 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; } -- 2.7.4