ftrace: Synchronize the initialization of ftrace_opsgrafted

There's some internal state that ftrace_ops needs to have set, but since
it can be declared outside of the ftrace.c code, it calls
ftrace_ops_init() on the ops in every global function. The issue is that
if two tasks call it on the same ops at the same time it is possible to
have the initialization of one corrupt the initialization of the other
call.

Create a ops_mutex to use to synchronize every initialization of the
ftrace_ops. The mutex is taken within checking the ftrace_ops flag that
states it was initializied but the flag is checked again after the mutex
has been taken. Checking first outside the mutex allows it to shortcut
having to take the mutex. But then the check needs to be done again after
the mute is taken in case of races.

Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260902095501.6b59af20@gandalf.local.home
Fixes: f04f24fb7e48d ("ftrace, kprobes: Fix a deadlock on ftrace_regex_lock")
Reported-by: sashiko-bot@kernel.org
Close: https://lore.kernel.org/all/20260829025528.49A831F000E9@smtp.kernel.org/
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 256 insertions, 0 deletions

diff --git a/tools/perf/bench/futex-hash.c b/tools/perf/bench/futex-hash.c
new file mode 100644
index 000000000..7e29f04da
--- /dev/null
+++ b/tools/perf/bench/futex-hash.c
@@ -0,0 +1,256 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2013  Davidlohr Bueso <davidlohr@hp.com>
+ *
+ * futex-hash: Stress the hell out of the Linux kernel futex uaddr hashing.
+ *
+ * This program is particularly useful for measuring the kernel's futex hash
+ * table/function implementation. In order for it to make sense, use with as
+ * many threads and futexes as possible.
+ */
+
+/* For the CLR_() macros */
+#include <string.h>
+#include <pthread.h>
+
+#include <errno.h>
+#include <signal.h>
+#include <stdlib.h>
+#include <linux/compiler.h>
+#include <linux/kernel.h>
+#include <linux/zalloc.h>
+#include <sys/time.h>
+#include <sys/mman.h>
+#include <sys/prctl.h>
+#include <perf/cpumap.h>
+
+#include "../util/mutex.h"
+#include "../util/stat.h"
+#include <subcmd/parse-options.h>
+#include "bench.h"
+#include "futex.h"
+
+#include <err.h>
+
+static bool done = false;
+static int futex_flag = 0;
+
+struct timeval bench__start, bench__end, bench__runtime;
+static struct mutex thread_lock;
+static unsigned int threads_starting;
+static struct stats throughput_stats;
+static struct cond thread_parent, thread_worker;
+
+struct worker {
+	int tid;
+	u_int32_t *futex;
+	pthread_t thread;
+	unsigned long ops;
+};
+
+static struct bench_futex_parameters params = {
+	.nfutexes = 1024,
+	.runtime  = 10,
+	.nbuckets = -1,
+};
+
+static const struct option options[] = {
+	OPT_INTEGER( 'b', "buckets", &params.nbuckets, "Specify amount of hash buckets"),
+	OPT_UINTEGER('t', "threads", &params.nthreads, "Specify amount of threads"),
+	OPT_UINTEGER('r', "runtime", &params.runtime, "Specify runtime (in seconds)"),
+	OPT_UINTEGER('f', "futexes", &params.nfutexes, "Specify amount of futexes per threads"),
+	OPT_BOOLEAN( 's', "silent",  &params.silent, "Silent mode: do not display data/details"),
+	OPT_BOOLEAN( 'S', "shared",  &params.fshared, "Use shared futexes instead of private ones"),
+	OPT_BOOLEAN( 'm', "mlockall", &params.mlockall, "Lock all current and future memory"),
+	OPT_END()
+};
+
+static const char * const bench_futex_hash_usage[] = {
+	"perf bench futex hash <options>",
+	NULL
+};
+
+static void *workerfn(void *arg)
+{
+	int ret;
+	struct worker *w = (struct worker *) arg;
+	unsigned int i;
+	unsigned long ops = w->ops; /* avoid cacheline bouncing */
+
+	mutex_lock(&thread_lock);
+	threads_starting--;
+	if (!threads_starting)
+		cond_signal(&thread_parent);
+	cond_wait(&thread_worker, &thread_lock);
+	mutex_unlock(&thread_lock);
+
+	do {
+		for (i = 0; i < params.nfutexes; i++, ops++) {
+			/*
+			 * We want the futex calls to fail in order to stress
+			 * the hashing of uaddr and not measure other steps,
+			 * such as internal waitqueue handling, thus enlarging
+			 * the critical region protected by hb->lock.
+			 */
+			ret = futex_wait(&w->futex[i], 1234, NULL, futex_flag);
+			if (!params.silent &&
+			    (!ret || errno != EAGAIN || errno != EWOULDBLOCK))
+				warn("Non-expected futex return call");
+		}
+	}  while (!done);
+
+	w->ops = ops;
+	return NULL;
+}
+
+static void toggle_done(int sig __maybe_unused,
+			siginfo_t *info __maybe_unused,
+			void *uc __maybe_unused)
+{
+	/* inform all threads that we're done for the day */
+	done = true;
+	gettimeofday(&bench__end, NULL);
+	timersub(&bench__end, &bench__start, &bench__runtime);
+}
+
+static void print_summary(void)
+{
+	unsigned long avg = avg_stats(&throughput_stats);
+	double stddev = stddev_stats(&throughput_stats);
+
+	printf("%sAveraged %ld operations/sec (+- %.2f%%), total secs = %d\n",
+	       !params.silent ? "\n" : "", avg, rel_stddev_stats(stddev, avg),
+	       (int)bench__runtime.tv_sec);
+	futex_print_nbuckets(&params);
+}
+
+int bench_futex_hash(int argc, const char **argv)
+{
+	int ret = 0;
+	cpu_set_t *cpuset;
+	struct sigaction act;
+	unsigned int i;
+	pthread_attr_t thread_attr;
+	struct worker *worker = NULL;
+	struct perf_cpu_map *cpu;
+	int nrcpus;
+	size_t size;
+
+	argc = parse_options(argc, argv, options, bench_futex_hash_usage, 0);
+	if (argc) {
+		usage_with_options(bench_futex_hash_usage, options);
+		exit(EXIT_FAILURE);
+	}
+
+	cpu = perf_cpu_map__new_online_cpus();
+	if (!cpu)
+		goto errmem;
+
+	memset(&act, 0, sizeof(act));
+	sigfillset(&act.sa_mask);
+	act.sa_sigaction = toggle_done;
+	sigaction(SIGINT, &act, NULL);
+
+	if (params.mlockall) {
+		if (mlockall(MCL_CURRENT | MCL_FUTURE))
+			err(EXIT_FAILURE, "mlockall");
+	}
+
+	if (!params.nthreads) /* default to the number of CPUs */
+		params.nthreads = perf_cpu_map__nr(cpu);
+
+	worker = calloc(params.nthreads, sizeof(*worker));
+	if (!worker)
+		goto errmem;
+
+	if (!params.fshared)
+		futex_flag = FUTEX_PRIVATE_FLAG;
+	futex_set_nbuckets_param(&params);
+
+	printf("Run summary [PID %d]: %d threads, each operating on %d [%s] futexes for %d secs.\n\n",
+	       getpid(), params.nthreads, params.nfutexes, params.fshared ? "shared":"private", params.runtime);
+
+	init_stats(&throughput_stats);
+	mutex_init(&thread_lock);
+	cond_init(&thread_parent);
+	cond_init(&thread_worker);
+
+	threads_starting = params.nthreads;
+	pthread_attr_init(&thread_attr);
+	gettimeofday(&bench__start, NULL);
+
+	nrcpus = cpu__max_cpu().cpu;
+	cpuset = CPU_ALLOC(nrcpus);
+	BUG_ON(!cpuset);
+	size = CPU_ALLOC_SIZE(nrcpus);
+
+	for (i = 0; i < params.nthreads; i++) {
+		worker[i].tid = i;
+		worker[i].futex = calloc(params.nfutexes, sizeof(*worker[i].futex));
+		if (!worker[i].futex)
+			goto errmem;
+
+		CPU_ZERO_S(size, cpuset);
+
+		CPU_SET_S(perf_cpu_map__cpu(cpu, i % perf_cpu_map__nr(cpu)).cpu, size, cpuset);
+		ret = pthread_attr_setaffinity_np(&thread_attr, size, cpuset);
+		if (ret) {
+			CPU_FREE(cpuset);
+			err(EXIT_FAILURE, "pthread_attr_setaffinity_np");
+		}
+		ret = pthread_create(&worker[i].thread, &thread_attr, workerfn,
+				     (void *)(struct worker *) &worker[i]);
+		if (ret) {
+			CPU_FREE(cpuset);
+			err(EXIT_FAILURE, "pthread_create");
+		}
+
+	}
+	CPU_FREE(cpuset);
+	pthread_attr_destroy(&thread_attr);
+
+	mutex_lock(&thread_lock);
+	while (threads_starting)
+		cond_wait(&thread_parent, &thread_lock);
+	cond_broadcast(&thread_worker);
+	mutex_unlock(&thread_lock);
+
+	sleep(params.runtime);
+	toggle_done(0, NULL, NULL);
+
+	for (i = 0; i < params.nthreads; i++) {
+		ret = pthread_join(worker[i].thread, NULL);
+		if (ret)
+			err(EXIT_FAILURE, "pthread_join");
+	}
+
+	/* cleanup & report results */
+	cond_destroy(&thread_parent);
+	cond_destroy(&thread_worker);
+	mutex_destroy(&thread_lock);
+
+	for (i = 0; i < params.nthreads; i++) {
+		unsigned long t = bench__runtime.tv_sec > 0 ?
+			worker[i].ops / bench__runtime.tv_sec : 0;
+		update_stats(&throughput_stats, t);
+		if (!params.silent) {
+			if (params.nfutexes == 1)
+				printf("[thread %2d] futex: %p [ %ld ops/sec ]\n",
+				       worker[i].tid, &worker[i].futex[0], t);
+			else
+				printf("[thread %2d] futexes: %p ... %p [ %ld ops/sec ]\n",
+				       worker[i].tid, &worker[i].futex[0],
+				       &worker[i].futex[params.nfutexes-1], t);
+		}
+
+		zfree(&worker[i].futex);
+	}
+
+	print_summary();
+
+	free(worker);
+	free(cpu);
+	return ret;
+errmem:
+	err(EXIT_FAILURE, "calloc");
+}