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, 262 insertions, 0 deletions

diff --git a/tools/perf/bench/breakpoint.c b/tools/perf/bench/breakpoint.c
new file mode 100644
index 000000000..1b7cd4481
--- /dev/null
+++ b/tools/perf/bench/breakpoint.c
@@ -0,0 +1,262 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <subcmd/parse-options.h>
+#include <linux/hw_breakpoint.h>
+#include <linux/perf_event.h>
+#include <linux/time64.h>
+#include <sys/syscall.h>
+#include <sys/ioctl.h>
+#include <sys/time.h>
+#include <pthread.h>
+#include <stddef.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <errno.h>
+#include "bench.h"
+#include "futex.h"
+
+static struct {
+	unsigned int nbreakpoints;
+	unsigned int nparallel;
+	unsigned int nthreads;
+} thread_params = {
+	.nbreakpoints = 1,
+	.nparallel = 1,
+	.nthreads = 1,
+};
+
+static const struct option thread_options[] = {
+	OPT_UINTEGER('b', "breakpoints", &thread_params.nbreakpoints,
+		"Specify amount of breakpoints"),
+	OPT_UINTEGER('p', "parallelism", &thread_params.nparallel, "Specify amount of parallelism"),
+	OPT_UINTEGER('t', "threads", &thread_params.nthreads, "Specify amount of threads"),
+	OPT_END()
+};
+
+static const char * const thread_usage[] = {
+	"perf bench breakpoint thread <options>",
+	NULL
+};
+
+struct breakpoint {
+	int fd;
+	char watched;
+};
+
+static int breakpoint_setup(void *addr)
+{
+	struct perf_event_attr attr = { .size = 0, };
+	int fd;
+
+	attr.type = PERF_TYPE_BREAKPOINT;
+	attr.size = sizeof(attr);
+	attr.inherit = 1;
+	attr.exclude_kernel = 1;
+	attr.exclude_hv = 1;
+	attr.bp_addr = (unsigned long)addr;
+	attr.bp_type = HW_BREAKPOINT_RW;
+	attr.bp_len = HW_BREAKPOINT_LEN_1;
+	fd = syscall(SYS_perf_event_open, &attr, 0, -1, -1, 0);
+
+	if (fd < 0)
+		fd = -errno;
+
+	return fd;
+}
+
+static void *passive_thread(void *arg)
+{
+	unsigned int *done = (unsigned int *)arg;
+
+	while (!__atomic_load_n(done, __ATOMIC_RELAXED))
+		futex_wait(done, 0, NULL, 0);
+	return NULL;
+}
+
+static void *active_thread(void *arg)
+{
+	unsigned int *done = (unsigned int *)arg;
+
+	while (!__atomic_load_n(done, __ATOMIC_RELAXED));
+	return NULL;
+}
+
+static void *breakpoint_thread(void *arg)
+{
+	unsigned int i, done;
+	int *repeat = (int *)arg;
+	pthread_t *threads;
+
+	threads = calloc(thread_params.nthreads, sizeof(threads[0]));
+	if (!threads)
+		exit((perror("calloc"), EXIT_FAILURE));
+
+	while (__atomic_fetch_sub(repeat, 1, __ATOMIC_RELAXED) > 0) {
+		done = 0;
+		for (i = 0; i < thread_params.nthreads; i++) {
+			if (pthread_create(&threads[i], NULL, passive_thread, &done))
+				exit((perror("pthread_create"), EXIT_FAILURE));
+		}
+		__atomic_store_n(&done, 1, __ATOMIC_RELAXED);
+		futex_wake(&done, thread_params.nthreads, 0);
+		for (i = 0; i < thread_params.nthreads; i++)
+			pthread_join(threads[i], NULL);
+	}
+	free(threads);
+	return NULL;
+}
+
+// The benchmark creates nbreakpoints inheritable breakpoints,
+// then starts nparallel threads which create and join bench_repeat batches of nthreads threads.
+int bench_breakpoint_thread(int argc, const char **argv)
+{
+	unsigned int i, result_usec;
+	int repeat = bench_repeat;
+	struct breakpoint *breakpoints;
+	pthread_t *parallel;
+	struct timeval start, stop, diff;
+
+	if (parse_options(argc, argv, thread_options, thread_usage, 0)) {
+		usage_with_options(thread_usage, thread_options);
+		exit(EXIT_FAILURE);
+	}
+	breakpoints = calloc(thread_params.nbreakpoints, sizeof(breakpoints[0]));
+	parallel = calloc(thread_params.nparallel, sizeof(parallel[0]));
+	if (!breakpoints || !parallel)
+		exit((perror("calloc"), EXIT_FAILURE));
+
+	for (i = 0; i < thread_params.nbreakpoints; i++) {
+		breakpoints[i].fd = breakpoint_setup(&breakpoints[i].watched);
+
+		if (breakpoints[i].fd < 0) {
+			if (breakpoints[i].fd == -ENODEV) {
+				printf("Skipping perf bench breakpoint thread: No hardware support\n");
+				return 0;
+			}
+			exit((perror("perf_event_open"), EXIT_FAILURE));
+		}
+	}
+	gettimeofday(&start, NULL);
+	for (i = 0; i < thread_params.nparallel; i++) {
+		if (pthread_create(&parallel[i], NULL, breakpoint_thread, &repeat))
+			exit((perror("pthread_create"), EXIT_FAILURE));
+	}
+	for (i = 0; i < thread_params.nparallel; i++)
+		pthread_join(parallel[i], NULL);
+	gettimeofday(&stop, NULL);
+	timersub(&stop, &start, &diff);
+	for (i = 0; i < thread_params.nbreakpoints; i++)
+		close(breakpoints[i].fd);
+	free(parallel);
+	free(breakpoints);
+	switch (bench_format) {
+	case BENCH_FORMAT_DEFAULT:
+		printf("# Created/joined %d threads with %d breakpoints and %d parallelism\n",
+			bench_repeat, thread_params.nbreakpoints, thread_params.nparallel);
+		printf(" %14s: %lu.%03lu [sec]\n\n", "Total time",
+			(long)diff.tv_sec, (long)(diff.tv_usec / USEC_PER_MSEC));
+		result_usec = diff.tv_sec * USEC_PER_SEC + diff.tv_usec;
+		printf(" %14lf usecs/op\n",
+			(double)result_usec / bench_repeat / thread_params.nthreads);
+		printf(" %14lf usecs/op/cpu\n",
+			(double)result_usec / bench_repeat /
+			thread_params.nthreads * thread_params.nparallel);
+		break;
+	case BENCH_FORMAT_SIMPLE:
+		printf("%lu.%03lu\n", (long)diff.tv_sec, (long)(diff.tv_usec / USEC_PER_MSEC));
+		break;
+	default:
+		fprintf(stderr, "Unknown format: %d\n", bench_format);
+		exit(EXIT_FAILURE);
+	}
+	return 0;
+}
+
+static struct {
+	unsigned int npassive;
+	unsigned int nactive;
+} enable_params = {
+	.nactive = 0,
+	.npassive = 0,
+};
+
+static const struct option enable_options[] = {
+	OPT_UINTEGER('p', "passive", &enable_params.npassive, "Specify amount of passive threads"),
+	OPT_UINTEGER('a', "active", &enable_params.nactive, "Specify amount of active threads"),
+	OPT_END()
+};
+
+static const char * const enable_usage[] = {
+	"perf bench breakpoint enable <options>",
+	NULL
+};
+
+// The benchmark creates an inheritable breakpoint,
+// then starts npassive threads that block and nactive threads that actively spin
+// and then disables and enables the breakpoint bench_repeat times.
+int bench_breakpoint_enable(int argc, const char **argv)
+{
+	unsigned int i, nthreads, result_usec, done = 0;
+	char watched;
+	int fd;
+	pthread_t *threads;
+	struct timeval start, stop, diff;
+
+	if (parse_options(argc, argv, enable_options, enable_usage, 0)) {
+		usage_with_options(enable_usage, enable_options);
+		exit(EXIT_FAILURE);
+	}
+	fd = breakpoint_setup(&watched);
+
+	if (fd < 0) {
+		if (fd == -ENODEV) {
+			printf("Skipping perf bench breakpoint enable: No hardware support\n");
+			return 0;
+		}
+		exit((perror("perf_event_open"), EXIT_FAILURE));
+	}
+	nthreads = enable_params.npassive + enable_params.nactive;
+	threads = calloc(nthreads, sizeof(threads[0]));
+	if (!threads)
+		exit((perror("calloc"), EXIT_FAILURE));
+
+	for (i = 0; i < nthreads; i++) {
+		if (pthread_create(&threads[i], NULL,
+			i < enable_params.npassive ? passive_thread : active_thread, &done))
+			exit((perror("pthread_create"), EXIT_FAILURE));
+	}
+	usleep(10000);  // let the threads block
+	gettimeofday(&start, NULL);
+	for (i = 0; i < bench_repeat; i++) {
+		if (ioctl(fd, PERF_EVENT_IOC_DISABLE, 0))
+			exit((perror("ioctl(PERF_EVENT_IOC_DISABLE)"), EXIT_FAILURE));
+		if (ioctl(fd, PERF_EVENT_IOC_ENABLE, 0))
+			exit((perror("ioctl(PERF_EVENT_IOC_ENABLE)"), EXIT_FAILURE));
+	}
+	gettimeofday(&stop, NULL);
+	timersub(&stop, &start, &diff);
+	__atomic_store_n(&done, 1, __ATOMIC_RELAXED);
+	futex_wake(&done, enable_params.npassive, 0);
+	for (i = 0; i < nthreads; i++)
+		pthread_join(threads[i], NULL);
+	free(threads);
+	close(fd);
+	switch (bench_format) {
+	case BENCH_FORMAT_DEFAULT:
+		printf("# Enabled/disabled breakpoint %d time with %d passive and %d active threads\n",
+			bench_repeat, enable_params.npassive, enable_params.nactive);
+		printf(" %14s: %lu.%03lu [sec]\n\n", "Total time",
+			(long)diff.tv_sec, (long)(diff.tv_usec / USEC_PER_MSEC));
+		result_usec = diff.tv_sec * USEC_PER_SEC + diff.tv_usec;
+		printf(" %14lf usecs/op\n", (double)result_usec / bench_repeat);
+		break;
+	case BENCH_FORMAT_SIMPLE:
+		printf("%lu.%03lu\n", (long)diff.tv_sec, (long)(diff.tv_usec / USEC_PER_MSEC));
+		break;
+	default:
+		fprintf(stderr, "Unknown format: %d\n", bench_format);
+		exit(EXIT_FAILURE);
+	}
+	return 0;
+}