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, 100 insertions, 0 deletions

diff --git a/arch/arm/mach-spear/hotplug.c b/arch/arm/mach-spear/hotplug.c
new file mode 100644
index 000000000..82a83c3cf
--- /dev/null
+++ b/arch/arm/mach-spear/hotplug.c
@@ -0,0 +1,100 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * linux/arch/arm/mach-spear13xx/hotplug.c
+ *
+ * Copyright (C) 2012 ST Microelectronics Ltd.
+ * Deepak Sikri <deepak.sikri@st.com>
+ *
+ * based upon linux/arch/arm/mach-realview/hotplug.c
+ */
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/smp.h>
+#include <asm/cp15.h>
+#include <asm/smp_plat.h>
+
+#include "generic.h"
+
+static inline void cpu_enter_lowpower(void)
+{
+	unsigned int v;
+
+	asm volatile(
+	"	mcr	p15, 0, %1, c7, c5, 0\n"
+	"	dsb\n"
+	/*
+	 * Turn off coherency
+	 */
+	"	mrc	p15, 0, %0, c1, c0, 1\n"
+	"	bic	%0, %0, #0x20\n"
+	"	mcr	p15, 0, %0, c1, c0, 1\n"
+	"	mrc	p15, 0, %0, c1, c0, 0\n"
+	"	bic	%0, %0, %2\n"
+	"	mcr	p15, 0, %0, c1, c0, 0\n"
+	: "=&r" (v)
+	: "r" (0), "Ir" (CR_C)
+	: "cc", "memory");
+}
+
+static inline void cpu_leave_lowpower(void)
+{
+	unsigned int v;
+
+	asm volatile("mrc	p15, 0, %0, c1, c0, 0\n"
+	"	orr	%0, %0, %1\n"
+	"	mcr	p15, 0, %0, c1, c0, 0\n"
+	"	mrc	p15, 0, %0, c1, c0, 1\n"
+	"	orr	%0, %0, #0x20\n"
+	"	mcr	p15, 0, %0, c1, c0, 1\n"
+	: "=&r" (v)
+	: "Ir" (CR_C)
+	: "cc");
+}
+
+static inline void spear13xx_do_lowpower(unsigned int cpu, int *spurious)
+{
+	for (;;) {
+		wfi();
+
+		if (spear_pen_release == cpu) {
+			/*
+			 * OK, proper wakeup, we're done
+			 */
+			break;
+		}
+
+		/*
+		 * Getting here, means that we have come out of WFI without
+		 * having been woken up - this shouldn't happen
+		 *
+		 * Just note it happening - when we're woken, we can report
+		 * its occurrence.
+		 */
+		(*spurious)++;
+	}
+}
+
+/*
+ * platform-specific code to shutdown a CPU
+ *
+ * Called with IRQs disabled
+ */
+void spear13xx_cpu_die(unsigned int cpu)
+{
+	int spurious = 0;
+
+	/*
+	 * we're ready for shutdown now, so do it
+	 */
+	cpu_enter_lowpower();
+	spear13xx_do_lowpower(cpu, &spurious);
+
+	/*
+	 * bring this CPU back into the world of cache
+	 * coherency, and then restore interrupts
+	 */
+	cpu_leave_lowpower();
+
+	if (spurious)
+		pr_warn("CPU%u: %u spurious wakeup calls\n", cpu, spurious);
+}