selftests/bpf: Test rhtab kptr cancellation semanticsgrafted

Resizable hash-map updates and deletions must not perform full special-field
destruction in their caller context. In particular, a referenced kptr must
remain attached to the allocation until the memory allocator destructor can
release it safely.

Add separate coverage for both affected paths. The update test stores a task
kptr, replaces the ordinary value bytes with BPF_EXIST, and verifies that the
kptr survived. The delete test removes an element and exchanges its kptr
through the still-valid map-value pointer before the allocation is reclaimed.

Both cases observe a NULL kptr when rhtab uses bpf_obj_free_fields(). They
recover and release the reference after rhtab switches to cancellation
semantics.

Signed-off-by: Nuoqi Gui <gnq25@mails.tsinghua.edu.cn>
[ kkd: Split update and delete coverage and rewrote the commit log ]
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20260904104203.345917-5-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 161 insertions, 0 deletions

diff --git a/tools/perf/tests/task-exit.c b/tools/perf/tests/task-exit.c
new file mode 100644
index 000000000..4053ff281
--- /dev/null
+++ b/tools/perf/tests/task-exit.c
@@ -0,0 +1,161 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "debug.h"
+#include "evlist.h"
+#include "evsel.h"
+#include "target.h"
+#include "thread_map.h"
+#include "tests.h"
+#include "util/mmap.h"
+
+#include <errno.h>
+#include <signal.h>
+#include <linux/string.h>
+#include <perf/cpumap.h>
+#include <perf/evlist.h>
+#include <perf/mmap.h>
+
+static int exited;
+static int nr_exit;
+
+static void sig_handler(int sig __maybe_unused)
+{
+	exited = 1;
+}
+
+/*
+ * evlist__prepare_workload will send a SIGUSR1 if the fork fails, since
+ * we asked by setting its exec_error to this handler.
+ */
+static void workload_exec_failed_signal(int signo __maybe_unused,
+					siginfo_t *info __maybe_unused,
+					void *ucontext __maybe_unused)
+{
+	exited	= 1;
+	nr_exit = -1;
+}
+
+/*
+ * This test will start a workload that does nothing then it checks
+ * if the number of exit event reported by the kernel is 1 or not
+ * in order to check the kernel returns correct number of event.
+ */
+static int test__task_exit(struct test_suite *test __maybe_unused, int subtest __maybe_unused)
+{
+	int err = -1;
+	union perf_event *event;
+	struct evsel *evsel;
+	struct evlist *evlist;
+	struct target target = {
+		.uses_mmap	= true,
+	};
+	const char *argv[] = { "true", NULL };
+	char sbuf[STRERR_BUFSIZE];
+	struct perf_cpu_map *cpus;
+	struct perf_thread_map *threads;
+	struct mmap *md;
+	int retry_count = 0;
+
+	signal(SIGCHLD, sig_handler);
+
+	evlist = evlist__new_dummy();
+	if (evlist == NULL) {
+		pr_debug("evlist__new_dummy\n");
+		return -1;
+	}
+
+	/*
+	 * Create maps of threads and cpus to monitor. In this case
+	 * we start with all threads and cpus (-1, -1) but then in
+	 * evlist__prepare_workload we'll fill in the only thread
+	 * we're monitoring, the one forked there.
+	 */
+	cpus = perf_cpu_map__new_any_cpu();
+	threads = thread_map__new_by_tid(-1);
+	if (!cpus || !threads) {
+		err = -ENOMEM;
+		pr_debug("Not enough memory to create thread/cpu maps\n");
+		goto out_delete_evlist;
+	}
+
+	perf_evlist__set_maps(&evlist->core, cpus, threads);
+
+	err = evlist__prepare_workload(evlist, &target, argv, false, workload_exec_failed_signal);
+	if (err < 0) {
+		pr_debug("Couldn't run the workload!\n");
+		goto out_delete_evlist;
+	}
+
+	evsel = evlist__first(evlist);
+	evsel->core.attr.task = 1;
+#ifdef __s390x__
+	evsel->core.attr.sample_freq = 1000000;
+#else
+	evsel->core.attr.sample_freq = 1;
+#endif
+	evsel->core.attr.inherit = 0;
+	evsel->core.attr.watermark = 0;
+	evsel->core.attr.wakeup_events = 1;
+	evsel->core.attr.exclude_kernel = 1;
+
+	err = evlist__open(evlist);
+	if (err < 0) {
+		pr_debug("Couldn't open the evlist: %s\n",
+			 str_error_r(-err, sbuf, sizeof(sbuf)));
+		goto out_delete_evlist;
+	}
+
+	if (evlist__mmap(evlist, 128) < 0) {
+		pr_debug("failed to mmap events: %d (%s)\n", errno,
+			 str_error_r(errno, sbuf, sizeof(sbuf)));
+		err = -1;
+		goto out_delete_evlist;
+	}
+
+	evlist__start_workload(evlist);
+
+retry:
+	md = &evlist->mmap[0];
+	if (perf_mmap__read_init(&md->core) < 0)
+		goto out_init;
+
+	while ((event = perf_mmap__read_event(&md->core)) != NULL) {
+		if (event->header.type == PERF_RECORD_EXIT)
+			nr_exit++;
+
+		perf_mmap__consume(&md->core);
+	}
+	perf_mmap__read_done(&md->core);
+
+out_init:
+	if (!exited || !nr_exit) {
+		evlist__poll(evlist, -1);
+
+		if (retry_count++ > 1000) {
+			pr_debug("Failed after retrying 1000 times\n");
+			err = -1;
+			goto out_delete_evlist;
+		}
+
+		goto retry;
+	}
+
+	if (nr_exit != 1) {
+		pr_debug("received %d EXIT records\n", nr_exit);
+		err = -1;
+	}
+
+out_delete_evlist:
+	perf_cpu_map__put(cpus);
+	perf_thread_map__put(threads);
+	evlist__delete(evlist);
+	return err;
+}
+
+struct test_case tests__task_exit[] = {
+	TEST_CASE_EXCLUSIVE("Number of exit events of a simple workload", task_exit),
+	{	.name = NULL, }
+};
+struct test_suite suite__task_exit = {
+	.desc = "Number of exit events of a simple workload",
+	.test_cases = tests__task_exit,
+};