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>

3 files changed, 126 insertions, 0 deletions

diff --git a/tools/testing/selftests/filelock/.gitignore b/tools/testing/selftests/filelock/.gitignore
new file mode 100644
index 000000000..825e899a1
--- /dev/null
+++ b/tools/testing/selftests/filelock/.gitignore
@@ -0,0 +1 @@
+ofdlocks
diff --git a/tools/testing/selftests/filelock/Makefile b/tools/testing/selftests/filelock/Makefile
new file mode 100644
index 000000000..478e82f8b
--- /dev/null
+++ b/tools/testing/selftests/filelock/Makefile
@@ -0,0 +1,5 @@
+# SPDX-License-Identifier: GPL-2.0
+
+TEST_GEN_PROGS := ofdlocks
+
+include ../lib.mk
diff --git a/tools/testing/selftests/filelock/ofdlocks.c b/tools/testing/selftests/filelock/ofdlocks.c
new file mode 100644
index 000000000..68bac28b2
--- /dev/null
+++ b/tools/testing/selftests/filelock/ofdlocks.c
@@ -0,0 +1,120 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#define _GNU_SOURCE
+#include <fcntl.h>
+#include <assert.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <string.h>
+#include "kselftest.h"
+
+static int lock_set(int fd, struct flock *fl)
+{
+	int ret;
+
+	fl->l_pid = 0;		// needed for OFD locks
+	fl->l_whence = SEEK_SET;
+	ret = fcntl(fd, F_OFD_SETLK, fl);
+	if (ret)
+		ksft_perror("fcntl()");
+	return ret;
+}
+
+static int lock_get(int fd, struct flock *fl)
+{
+	int ret;
+
+	fl->l_pid = 0;		// needed for OFD locks
+	fl->l_whence = SEEK_SET;
+	ret = fcntl(fd, F_OFD_GETLK, fl);
+	if (ret)
+		ksft_perror("fcntl()");
+	return ret;
+}
+
+int main(void)
+{
+	int rc;
+	struct flock fl, fl2;
+	int fd = open("/tmp/aa", O_RDWR | O_CREAT | O_EXCL, 0600);
+	int fd2 = open("/tmp/aa", O_RDONLY);
+
+	ksft_print_header();
+	ksft_set_plan(4);
+
+	unlink("/tmp/aa");
+	assert(fd != -1);
+	assert(fd2 != -1);
+	ksft_print_msg("opened fds %i %i\n", fd, fd2);
+
+	/* Set some read lock */
+	fl.l_type = F_RDLCK;
+	fl.l_start = 5;
+	fl.l_len = 3;
+	rc = lock_set(fd, &fl);
+	ksft_test_result(rc == 0, "set OFD read lock on first fd\n");
+	if (rc != 0)
+		ksft_finished();
+
+	/* Make sure read locks do not conflict on different fds. */
+	fl.l_type = F_RDLCK;
+	fl.l_start = 5;
+	fl.l_len = 1;
+	rc = lock_get(fd2, &fl);
+	if (rc != 0)
+		ksft_finished();
+	if (fl.l_type != F_UNLCK)
+		ksft_exit_fail_msg("read locks conflicted\n");
+
+	/* Make sure read/write locks do conflict on different fds. */
+	fl.l_type = F_WRLCK;
+	fl.l_start = 5;
+	fl.l_len = 1;
+	rc = lock_get(fd2, &fl);
+	if (rc != 0)
+		ksft_finished();
+	ksft_test_result(fl.l_type != F_UNLCK,
+			 "read and write locks conflicted\n");
+	if (fl.l_type == F_UNLCK)
+		ksft_finished();
+
+	/* Get info about the lock on first fd. */
+	fl.l_type = F_UNLCK;
+	fl.l_start = 5;
+	fl.l_len = 1;
+	rc = lock_get(fd, &fl);
+	if (rc != 0)
+		ksft_exit_fail_msg("F_OFD_GETLK with F_UNLCK not supported\n");
+	ksft_test_result(fl.l_type != F_UNLCK,
+			 "F_OFD_GETLK with F_UNLCK returned lock info\n");
+	if (fl.l_type == F_UNLCK)
+		ksft_exit_fail();
+	ksft_print_msg("F_UNLCK test returns: locked, type %i pid %i len %zi\n",
+		       fl.l_type, fl.l_pid, fl.l_len);
+
+	/* Try the same but by locking everything by len==0. */
+	fl2.l_type = F_UNLCK;
+	fl2.l_start = 0;
+	fl2.l_len = 0;
+	rc = lock_get(fd, &fl2);
+	if (rc != 0)
+		ksft_exit_fail_msg
+		    ("F_OFD_GETLK with F_UNLCK not supported\n");
+	ksft_test_result(memcmp(&fl, &fl2, sizeof(fl)) == 0,
+			 "F_UNLCK with len==0 returned the same\n");
+	if (memcmp(&fl, &fl2, sizeof(fl))) {
+		ksft_exit_fail_msg
+		    ("F_UNLCK test returns: locked, type %i pid %i len %zi\n",
+		     fl.l_type, fl.l_pid, fl.l_len);
+	}
+
+	/* Get info about the lock on second fd - no locks on it. */
+	fl.l_type = F_UNLCK;
+	fl.l_start = 0;
+	fl.l_len = 0;
+	lock_get(fd2, &fl);
+	ksft_test_result(fl.l_type == F_UNLCK,
+			 "F_OFD_GETLK with F_UNLCK return lock info from another fd\n");
+
+	ksft_finished();
+}