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, 124 insertions, 0 deletions

diff --git a/drivers/accessibility/speakup/buffers.c b/drivers/accessibility/speakup/buffers.c
new file mode 100644
index 000000000..1371ced2f
--- /dev/null
+++ b/drivers/accessibility/speakup/buffers.c
@@ -0,0 +1,124 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/console.h>
+#include <linux/types.h>
+#include <linux/wait.h>
+
+#include "speakup.h"
+#include "spk_priv.h"
+
+#define SYNTH_BUF_SIZE 8192	/* currently 8K bytes */
+
+static u16 synth_buffer[SYNTH_BUF_SIZE];	/* guess what this is for! */
+static u16 *buff_in = synth_buffer;
+static u16 *buff_out = synth_buffer;
+static u16 *buffer_end = synth_buffer + SYNTH_BUF_SIZE - 1;
+
+/* These try to throttle applications by stopping the TTYs
+ * Note: we need to make sure that we will restart them eventually, which is
+ * usually not possible to do from the notifiers. TODO: it should be possible
+ * starting from linux 2.6.26.
+ *
+ * So we only stop when we know alive == 1 (else we discard the data anyway),
+ * and the alive synth will eventually call start_ttys from the thread context.
+ */
+void speakup_start_ttys(void)
+{
+	int i;
+
+	for (i = 0; i < MAX_NR_CONSOLES; i++) {
+		if (speakup_console[i] && speakup_console[i]->tty_stopped)
+			continue;
+		if (vc_cons[i].d && vc_cons[i].d->port.tty)
+			start_tty(vc_cons[i].d->port.tty);
+	}
+}
+EXPORT_SYMBOL_GPL(speakup_start_ttys);
+
+static void speakup_stop_ttys(void)
+{
+	int i;
+
+	for (i = 0; i < MAX_NR_CONSOLES; i++)
+		if (vc_cons[i].d && vc_cons[i].d->port.tty)
+			stop_tty(vc_cons[i].d->port.tty);
+}
+
+static int synth_buffer_free(void)
+{
+	int chars_free;
+
+	if (buff_in >= buff_out)
+		chars_free = SYNTH_BUF_SIZE - (buff_in - buff_out);
+	else
+		chars_free = buff_out - buff_in;
+	return chars_free;
+}
+
+int synth_buffer_empty(void)
+{
+	return (buff_in == buff_out);
+}
+EXPORT_SYMBOL_GPL(synth_buffer_empty);
+
+void synth_buffer_add(u16 ch)
+{
+	if (!synth->alive) {
+		/* This makes sure that we won't stop TTYs if there is no synth
+		 * to restart them
+		 */
+		return;
+	}
+	if (synth_buffer_free() <= 100) {
+		synth_start();
+		speakup_stop_ttys();
+	}
+	if (synth_buffer_free() <= 1)
+		return;
+	*buff_in++ = ch;
+	if (buff_in > buffer_end)
+		buff_in = synth_buffer;
+	/* We have written something to the speech synthesis, so we are not
+	 * paused any more.
+	 */
+	spk_paused = false;
+}
+
+u16 synth_buffer_getc(void)
+{
+	u16 ch;
+
+	if (buff_out == buff_in)
+		return 0;
+	ch = *buff_out++;
+	if (buff_out > buffer_end)
+		buff_out = synth_buffer;
+	return ch;
+}
+EXPORT_SYMBOL_GPL(synth_buffer_getc);
+
+u16 synth_buffer_peek(void)
+{
+	if (buff_out == buff_in)
+		return 0;
+	return *buff_out;
+}
+EXPORT_SYMBOL_GPL(synth_buffer_peek);
+
+void synth_buffer_skip_nonlatin1(void)
+{
+	while (buff_out != buff_in) {
+		if (*buff_out < 0x100)
+			return;
+		buff_out++;
+		if (buff_out > buffer_end)
+			buff_out = synth_buffer;
+	}
+}
+EXPORT_SYMBOL_GPL(synth_buffer_skip_nonlatin1);
+
+void synth_buffer_clear(void)
+{
+	buff_in = synth_buffer;
+	buff_out = synth_buffer;
+}
+EXPORT_SYMBOL_GPL(synth_buffer_clear);