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, 65 insertions, 0 deletions

diff --git a/arch/powerpc/lib/locks.c b/arch/powerpc/lib/locks.c
new file mode 100644
index 000000000..04165b7a1
--- /dev/null
+++ b/arch/powerpc/lib/locks.c
@@ -0,0 +1,65 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Spin and read/write lock operations.
+ *
+ * Copyright (C) 2001-2004 Paul Mackerras <paulus@au.ibm.com>, IBM
+ * Copyright (C) 2001 Anton Blanchard <anton@au.ibm.com>, IBM
+ * Copyright (C) 2002 Dave Engebretsen <engebret@us.ibm.com>, IBM
+ *   Rework to support virtual processors
+ */
+
+#include <linux/kernel.h>
+#include <linux/spinlock.h>
+#include <linux/export.h>
+#include <linux/smp.h>
+
+/* waiting for a spinlock... */
+#if defined(CONFIG_PPC_SPLPAR)
+#include <asm/hvcall.h>
+#include <asm/smp.h>
+
+void splpar_spin_yield(arch_spinlock_t *lock)
+{
+	unsigned int lock_value, holder_cpu, yield_count;
+
+	lock_value = lock->slock;
+	if (lock_value == 0)
+		return;
+	holder_cpu = lock_value & 0xffff;
+	BUG_ON(holder_cpu >= NR_CPUS);
+
+	yield_count = yield_count_of(holder_cpu);
+	if ((yield_count & 1) == 0)
+		return;		/* virtual cpu is currently running */
+	rmb();
+	if (lock->slock != lock_value)
+		return;		/* something has changed */
+	yield_to_preempted(holder_cpu, yield_count);
+}
+EXPORT_SYMBOL_GPL(splpar_spin_yield);
+
+/*
+ * Waiting for a read lock or a write lock on a rwlock...
+ * This turns out to be the same for read and write locks, since
+ * we only know the holder if it is write-locked.
+ */
+void splpar_rw_yield(arch_rwlock_t *rw)
+{
+	int lock_value;
+	unsigned int holder_cpu, yield_count;
+
+	lock_value = rw->lock;
+	if (lock_value >= 0)
+		return;		/* no write lock at present */
+	holder_cpu = lock_value & 0xffff;
+	BUG_ON(holder_cpu >= NR_CPUS);
+
+	yield_count = yield_count_of(holder_cpu);
+	if ((yield_count & 1) == 0)
+		return;		/* virtual cpu is currently running */
+	rmb();
+	if (rw->lock != lock_value)
+		return;		/* something has changed */
+	yield_to_preempted(holder_cpu, yield_count);
+}
+#endif