Merge branch 'bpf-introduce-deferred-task-context-execution'

Mykyta Yatsenko says:

====================
bpf: Introduce deferred task context execution

From: Mykyta Yatsenko <yatsenko@meta.com>

This patch introduces a new mechanism for BPF programs to schedule
deferred execution in the context of a specific task using the kernel’s
task_work infrastructure.

The new bpf_task_work interface enables BPF use cases that
require sleepable subprogram execution within task context, for example,
scheduling sleepable function from the context that does not
allow sleepable, such as NMI.

Introduced kfuncs bpf_task_work_schedule_signal() and
bpf_task_work_schedule_resume() for scheduling BPF callbacks correspond
to different modes used by task_work (TWA_SIGNAL or TWA_RESUME).

The implementation manages scheduling state via metadata objects (struct
bpf_task_work_context). Pointers to bpf_task_work_context are stored
in BPF map values. State transitions are handled via an atomic
state machine (bpf_task_work_state) to ensure correctness under
concurrent usage and deletion, lifetime is guarded by refcounting and
RCU Tasks Trace.
Kfuncs call task_work_add() indirectly via irq_work to avoid locking in
potentially NMI context.

Changelog:
---
v7 -> v8
v7: https://lore.kernel.org/bpf/20250922232611.614512-1-mykyta.yatsenko5@gmail.com/
 * Fix unused variable warning in patch 1
 * Decrease stress test time from 2 to 1 second
 * Went through CI warnings, other than unused variable, there are just
 2 new in kernel/bpf/helpers.c related to newly introduced kfuncs, these
 look expected.

v6 -> v7
v6: https://lore.kernel.org/bpf/20250918132615.193388-1-mykyta.yatsenko5@gmail.com/
 * Added stress test
 * Extending refactoring in patch 1
 * Changing comment and removing one check for map->usercnt in patch 7

v5 -> v6
v5: https://lore.kernel.org/bpf/20250916233651.258458-1-mykyta.yatsenko5@gmail.com/
 * Fixing readability in verifier.c:check_map_field_pointer()
 * Removing BUG_ON from helpers.c

v4 -> v5
v4:
https://lore.kernel.org/all/20250915201820.248977-1-mykyta.yatsenko5@gmail.com/
 * Fix invalid/null pointer dereference bug, reported by syzbot
 * Nits in selftests

v3 -> v4
v3: https://lore.kernel.org/all/20250905164508.1489482-1-mykyta.yatsenko5@gmail.com/
 * Modify async callback return value processing in verifier, to allow
non-zero return values.
 * Change return type of the callback from void to int, as verifier
expects scalar value.
 * Switched to void* for bpf_map API kfunc arguments to avoid casts.
 * Addressing numerous nits and small improvements.

v2 -> v3
v2: https://lore.kernel.org/all/20250815192156.272445-1-mykyta.yatsenko5@gmail.com/
 * Introduce ref counting
 * Add patches with minor verifier and btf.c refactorings to avoid code
duplication
 * Rework initiation of the task work scheduling to handle race with map
usercnt dropping to zero
====================

Link: https://patch.msgid.link/20250923112404.668720-1-mykyta.yatsenko5@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

5 files changed, 556 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/prog_tests/task_work_stress.c b/tools/testing/selftests/bpf/prog_tests/task_work_stress.c
new file mode 100644
index 000000000000..450d17d91a56
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/task_work_stress.c
@@ -0,0 +1,130 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
+#include <test_progs.h>
+#include <string.h>
+#include <stdio.h>
+#include "task_work_stress.skel.h"
+#include <linux/bpf.h>
+#include <linux/perf_event.h>
+#include <sys/syscall.h>
+#include <time.h>
+#include <stdlib.h>
+#include <stdatomic.h>
+
+struct test_data {
+	int prog_fd;
+	atomic_int exit;
+};
+
+void *runner(void *test_data)
+{
+	struct test_data *td = test_data;
+	int err = 0;
+	LIBBPF_OPTS(bpf_test_run_opts, opts);
+
+	while (!err && !atomic_load(&td->exit))
+		err = bpf_prog_test_run_opts(td->prog_fd, &opts);
+
+	return NULL;
+}
+
+static int get_env_int(const char *str, int def)
+{
+	const char *s = getenv(str);
+	char *end;
+	int retval;
+
+	if (!s || !*s)
+		return def;
+	errno = 0;
+	retval = strtol(s, &end, 10);
+	if (errno || *end || retval < 0)
+		return def;
+	return retval;
+}
+
+static void task_work_run(bool enable_delete)
+{
+	struct task_work_stress *skel;
+	struct bpf_program *scheduler, *deleter;
+	int nthreads = 16;
+	int test_time_s = get_env_int("BPF_TASK_WORK_TEST_TIME", 1);
+	pthread_t tid[nthreads], tid_del;
+	bool started[nthreads], started_del = false;
+	struct test_data td_sched = { .exit = 0 }, td_del = { .exit = 1 };
+	int i, err;
+
+	skel = task_work_stress__open();
+	if (!ASSERT_OK_PTR(skel, "task_work__open"))
+		return;
+
+	scheduler = bpf_object__find_program_by_name(skel->obj, "schedule_task_work");
+	bpf_program__set_autoload(scheduler, true);
+
+	deleter = bpf_object__find_program_by_name(skel->obj, "delete_task_work");
+	bpf_program__set_autoload(deleter, true);
+
+	err = task_work_stress__load(skel);
+	if (!ASSERT_OK(err, "skel_load"))
+		goto cleanup;
+
+	for (i = 0; i < nthreads; ++i)
+		started[i] = false;
+
+	td_sched.prog_fd = bpf_program__fd(scheduler);
+	for (i = 0; i < nthreads; ++i) {
+		if (pthread_create(&tid[i], NULL, runner, &td_sched) != 0) {
+			fprintf(stderr, "could not start thread");
+			goto cancel;
+		}
+		started[i] = true;
+	}
+
+	if (enable_delete)
+		atomic_store(&td_del.exit, 0);
+
+	td_del.prog_fd = bpf_program__fd(deleter);
+	if (pthread_create(&tid_del, NULL, runner, &td_del) != 0) {
+		fprintf(stderr, "could not start thread");
+		goto cancel;
+	}
+	started_del = true;
+
+	/* Run stress test for some time */
+	sleep(test_time_s);
+
+cancel:
+	atomic_store(&td_sched.exit, 1);
+	atomic_store(&td_del.exit, 1);
+	for (i = 0; i < nthreads; ++i) {
+		if (started[i])
+			pthread_join(tid[i], NULL);
+	}
+
+	if (started_del)
+		pthread_join(tid_del, NULL);
+
+	ASSERT_GT(skel->bss->callback_scheduled, 0, "work scheduled");
+	/* Some scheduling attempts should have failed due to contention */
+	ASSERT_GT(skel->bss->schedule_error, 0, "schedule error");
+
+	if (enable_delete) {
+		/* If delete thread is enabled, it has cancelled some callbacks */
+		ASSERT_GT(skel->bss->delete_success, 0, "delete success");
+		ASSERT_LT(skel->bss->callback_success, skel->bss->callback_scheduled, "callbacks");
+	} else {
+		/* Without delete thread number of scheduled callbacks is the same as fired */
+		ASSERT_EQ(skel->bss->callback_success, skel->bss->callback_scheduled, "callbacks");
+	}
+
+cleanup:
+	task_work_stress__destroy(skel);
+}
+
+void test_task_work_stress(void)
+{
+	if (test__start_subtest("no_delete"))
+		task_work_run(false);
+	if (test__start_subtest("with_delete"))
+		task_work_run(true);
+}
diff --git a/tools/testing/selftests/bpf/prog_tests/test_task_work.c b/tools/testing/selftests/bpf/prog_tests/test_task_work.c
new file mode 100644
index 000000000000..666585270fbf
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/test_task_work.c
@@ -0,0 +1,150 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
+#include <test_progs.h>
+#include <string.h>
+#include <stdio.h>
+#include "task_work.skel.h"
+#include "task_work_fail.skel.h"
+#include <linux/bpf.h>
+#include <linux/perf_event.h>
+#include <sys/syscall.h>
+#include <time.h>
+
+static int perf_event_open(__u32 type, __u64 config, int pid)
+{
+	struct perf_event_attr attr = {
+		.type = type,
+		.config = config,
+		.size = sizeof(struct perf_event_attr),
+		.sample_period = 100000,
+	};
+
+	return syscall(__NR_perf_event_open, &attr, pid, -1, -1, 0);
+}
+
+struct elem {
+	char data[128];
+	struct bpf_task_work tw;
+};
+
+static int verify_map(struct bpf_map *map, const char *expected_data)
+{
+	int err;
+	struct elem value;
+	int processed_values = 0;
+	int k, sz;
+
+	sz = bpf_map__max_entries(map);
+	for (k = 0; k < sz; ++k) {
+		err = bpf_map__lookup_elem(map, &k, sizeof(int), &value, sizeof(struct elem), 0);
+		if (err)
+			continue;
+		if (!ASSERT_EQ(strcmp(expected_data, value.data), 0, "map data")) {
+			fprintf(stderr, "expected '%s', found '%s' in %s map", expected_data,
+				value.data, bpf_map__name(map));
+			return 2;
+		}
+		processed_values++;
+	}
+
+	return processed_values == 0;
+}
+
+static void task_work_run(const char *prog_name, const char *map_name)
+{
+	struct task_work *skel;
+	struct bpf_program *prog;
+	struct bpf_map *map;
+	struct bpf_link *link;
+	int err, pe_fd = 0, pid, status, pipefd[2];
+	char user_string[] = "hello world";
+
+	if (!ASSERT_NEQ(pipe(pipefd), -1, "pipe"))
+		return;
+
+	pid = fork();
+	if (pid == 0) {
+		__u64 num = 1;
+		int i;
+		char buf;
+
+		close(pipefd[1]);
+		read(pipefd[0], &buf, sizeof(buf));
+		close(pipefd[0]);
+
+		for (i = 0; i < 10000; ++i)
+			num *= time(0) % 7;
+		(void)num;
+		exit(0);
+	}
+	ASSERT_GT(pid, 0, "fork() failed");
+
+	skel = task_work__open();
+	if (!ASSERT_OK_PTR(skel, "task_work__open"))
+		return;
+
+	bpf_object__for_each_program(prog, skel->obj) {
+		bpf_program__set_autoload(prog, false);
+	}
+
+	prog = bpf_object__find_program_by_name(skel->obj, prog_name);
+	if (!ASSERT_OK_PTR(prog, "prog_name"))
+		goto cleanup;
+	bpf_program__set_autoload(prog, true);
+	skel->bss->user_ptr = (char *)user_string;
+
+	err = task_work__load(skel);
+	if (!ASSERT_OK(err, "skel_load"))
+		goto cleanup;
+
+	pe_fd = perf_event_open(PERF_TYPE_HARDWARE, PERF_COUNT_HW_CPU_CYCLES, pid);
+	if (pe_fd == -1 && (errno == ENOENT || errno == EOPNOTSUPP)) {
+		printf("%s:SKIP:no PERF_COUNT_HW_CPU_CYCLES\n", __func__);
+		test__skip();
+		goto cleanup;
+	}
+	if (!ASSERT_NEQ(pe_fd, -1, "pe_fd")) {
+		fprintf(stderr, "perf_event_open errno: %d, pid: %d\n", errno, pid);
+		goto cleanup;
+	}
+
+	link = bpf_program__attach_perf_event(prog, pe_fd);
+	if (!ASSERT_OK_PTR(link, "attach_perf_event"))
+		goto cleanup;
+
+	close(pipefd[0]);
+	write(pipefd[1], user_string, 1);
+	close(pipefd[1]);
+	/* Wait to collect some samples */
+	waitpid(pid, &status, 0);
+	pid = 0;
+	map = bpf_object__find_map_by_name(skel->obj, map_name);
+	if (!ASSERT_OK_PTR(map, "find map_name"))
+		goto cleanup;
+	if (!ASSERT_OK(verify_map(map, user_string), "verify map"))
+		goto cleanup;
+cleanup:
+	if (pe_fd >= 0)
+		close(pe_fd);
+	task_work__destroy(skel);
+	if (pid) {
+		close(pipefd[0]);
+		write(pipefd[1], user_string, 1);
+		close(pipefd[1]);
+		waitpid(pid, &status, 0);
+	}
+}
+
+void test_task_work(void)
+{
+	if (test__start_subtest("test_task_work_hash_map"))
+		task_work_run("oncpu_hash_map", "hmap");
+
+	if (test__start_subtest("test_task_work_array_map"))
+		task_work_run("oncpu_array_map", "arrmap");
+
+	if (test__start_subtest("test_task_work_lru_map"))
+		task_work_run("oncpu_lru_map", "lrumap");
+
+	RUN_TESTS(task_work_fail);
+}
diff --git a/tools/testing/selftests/bpf/progs/task_work.c b/tools/testing/selftests/bpf/progs/task_work.c
new file mode 100644
index 000000000000..23217f06a3ec
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/task_work.c
@@ -0,0 +1,107 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
+
+#include <vmlinux.h>
+#include <string.h>
+#include <stdbool.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include "bpf_misc.h"
+#include "errno.h"
+
+char _license[] SEC("license") = "GPL";
+
+const void *user_ptr = NULL;
+
+struct elem {
+	char data[128];
+	struct bpf_task_work tw;
+};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__uint(map_flags, BPF_F_NO_PREALLOC);
+	__uint(max_entries, 1);
+	__type(key, int);
+	__type(value, struct elem);
+} hmap SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, int);
+	__type(value, struct elem);
+} arrmap SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_LRU_HASH);
+	__uint(max_entries, 1);
+	__type(key, int);
+	__type(value, struct elem);
+} lrumap SEC(".maps");
+
+static int process_work(struct bpf_map *map, void *key, void *value)
+{
+	struct elem *work = value;
+
+	bpf_copy_from_user_str(work->data, sizeof(work->data), (const void *)user_ptr, 0);
+	return 0;
+}
+
+int key = 0;
+
+SEC("perf_event")
+int oncpu_hash_map(struct pt_regs *args)
+{
+	struct elem empty_work = { .data = { 0 } };
+	struct elem *work;
+	struct task_struct *task;
+	int err;
+
+	task = bpf_get_current_task_btf();
+	err = bpf_map_update_elem(&hmap, &key, &empty_work, BPF_NOEXIST);
+	if (err)
+		return 0;
+	work = bpf_map_lookup_elem(&hmap, &key);
+	if (!work)
+		return 0;
+
+	bpf_task_work_schedule_resume(task, &work->tw, &hmap, process_work, NULL);
+	return 0;
+}
+
+SEC("perf_event")
+int oncpu_array_map(struct pt_regs *args)
+{
+	struct elem *work;
+	struct task_struct *task;
+
+	task = bpf_get_current_task_btf();
+	work = bpf_map_lookup_elem(&arrmap, &key);
+	if (!work)
+		return 0;
+	bpf_task_work_schedule_signal(task, &work->tw, &arrmap, process_work, NULL);
+	return 0;
+}
+
+SEC("perf_event")
+int oncpu_lru_map(struct pt_regs *args)
+{
+	struct elem empty_work = { .data = { 0 } };
+	struct elem *work;
+	struct task_struct *task;
+	int err;
+
+	task = bpf_get_current_task_btf();
+	work = bpf_map_lookup_elem(&lrumap, &key);
+	if (work)
+		return 0;
+	err = bpf_map_update_elem(&lrumap, &key, &empty_work, BPF_NOEXIST);
+	if (err)
+		return 0;
+	work = bpf_map_lookup_elem(&lrumap, &key);
+	if (!work || work->data[0])
+		return 0;
+	bpf_task_work_schedule_resume(task, &work->tw, &lrumap, process_work, NULL);
+	return 0;
+}
diff --git a/tools/testing/selftests/bpf/progs/task_work_fail.c b/tools/testing/selftests/bpf/progs/task_work_fail.c
new file mode 100644
index 000000000000..77fe8f28facd
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/task_work_fail.c
@@ -0,0 +1,96 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
+
+#include <vmlinux.h>
+#include <string.h>
+#include <stdbool.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include "bpf_misc.h"
+
+char _license[] SEC("license") = "GPL";
+
+const void *user_ptr = NULL;
+
+struct elem {
+	char data[128];
+	struct bpf_task_work tw;
+};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__uint(map_flags, BPF_F_NO_PREALLOC);
+	__uint(max_entries, 1);
+	__type(key, int);
+	__type(value, struct elem);
+} hmap SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, int);
+	__type(value, struct elem);
+} arrmap SEC(".maps");
+
+static int process_work(struct bpf_map *map, void *key, void *value)
+{
+	struct elem *work = value;
+
+	bpf_copy_from_user_str(work->data, sizeof(work->data), (const void *)user_ptr, 0);
+	return 0;
+}
+
+int key = 0;
+
+SEC("perf_event")
+__failure __msg("doesn't match map pointer in R3")
+int mismatch_map(struct pt_regs *args)
+{
+	struct elem *work;
+	struct task_struct *task;
+
+	task = bpf_get_current_task_btf();
+	work = bpf_map_lookup_elem(&arrmap, &key);
+	if (!work)
+		return 0;
+	bpf_task_work_schedule_resume(task, &work->tw, &hmap, process_work, NULL);
+	return 0;
+}
+
+SEC("perf_event")
+__failure __msg("arg#1 doesn't point to a map value")
+int no_map_task_work(struct pt_regs *args)
+{
+	struct task_struct *task;
+	struct bpf_task_work tw;
+
+	task = bpf_get_current_task_btf();
+	bpf_task_work_schedule_resume(task, &tw, &hmap, process_work, NULL);
+	return 0;
+}
+
+SEC("perf_event")
+__failure __msg("Possibly NULL pointer passed to trusted arg1")
+int task_work_null(struct pt_regs *args)
+{
+	struct task_struct *task;
+
+	task = bpf_get_current_task_btf();
+	bpf_task_work_schedule_resume(task, NULL, &hmap, process_work, NULL);
+	return 0;
+}
+
+SEC("perf_event")
+__failure __msg("Possibly NULL pointer passed to trusted arg2")
+int map_null(struct pt_regs *args)
+{
+	struct elem *work;
+	struct task_struct *task;
+
+	task = bpf_get_current_task_btf();
+	work = bpf_map_lookup_elem(&arrmap, &key);
+	if (!work)
+		return 0;
+	bpf_task_work_schedule_resume(task, &work->tw, NULL, process_work, NULL);
+	return 0;
+}
diff --git a/tools/testing/selftests/bpf/progs/task_work_stress.c b/tools/testing/selftests/bpf/progs/task_work_stress.c
new file mode 100644
index 000000000000..90fca06fff56
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/task_work_stress.c
@@ -0,0 +1,73 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
+
+#include <vmlinux.h>
+#include <string.h>
+#include <stdbool.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include "bpf_misc.h"
+
+#define ENTRIES 128
+
+char _license[] SEC("license") = "GPL";
+
+__u64 callback_scheduled = 0;
+__u64 callback_success = 0;
+__u64 schedule_error = 0;
+__u64 delete_success = 0;
+
+struct elem {
+	__u32 count;
+	struct bpf_task_work tw;
+};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__uint(map_flags, BPF_F_NO_PREALLOC);
+	__uint(max_entries, ENTRIES);
+	__type(key, int);
+	__type(value, struct elem);
+} hmap SEC(".maps");
+
+static int process_work(struct bpf_map *map, void *key, void *value)
+{
+	__sync_fetch_and_add(&callback_success, 1);
+	return 0;
+}
+
+SEC("syscall")
+int schedule_task_work(void *ctx)
+{
+	struct elem empty_work = {.count = 0};
+	struct elem *work;
+	int key = 0, err;
+
+	key = bpf_ktime_get_ns() % ENTRIES;
+	work = bpf_map_lookup_elem(&hmap, &key);
+	if (!work) {
+		bpf_map_update_elem(&hmap, &key, &empty_work, BPF_NOEXIST);
+		work = bpf_map_lookup_elem(&hmap, &key);
+		if (!work)
+			return 0;
+	}
+	err = bpf_task_work_schedule_signal(bpf_get_current_task_btf(), &work->tw, &hmap,
+					    process_work, NULL);
+	if (err)
+		__sync_fetch_and_add(&schedule_error, 1);
+	else
+		__sync_fetch_and_add(&callback_scheduled, 1);
+	return 0;
+}
+
+SEC("syscall")
+int delete_task_work(void *ctx)
+{
+	int key = 0, err;
+
+	key = bpf_get_prandom_u32() % ENTRIES;
+	err = bpf_map_delete_elem(&hmap, &key);
+	if (!err)
+		__sync_fetch_and_add(&delete_success, 1);
+	return 0;
+}