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, 75 insertions, 0 deletions

diff --git a/drivers/clocksource/mmio.c b/drivers/clocksource/mmio.c
new file mode 100644
index 000000000..0fee8edb8
--- /dev/null
+++ b/drivers/clocksource/mmio.c
@@ -0,0 +1,75 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Generic MMIO clocksource support
+ */
+#include <linux/clocksource.h>
+#include <linux/errno.h>
+#include <linux/init.h>
+#include <linux/slab.h>
+
+struct clocksource_mmio {
+	void __iomem *reg;
+	struct clocksource clksrc;
+};
+
+static inline struct clocksource_mmio *to_mmio_clksrc(struct clocksource *c)
+{
+	return container_of(c, struct clocksource_mmio, clksrc);
+}
+
+u64 clocksource_mmio_readl_up(struct clocksource *c)
+{
+	return (u64)readl_relaxed(to_mmio_clksrc(c)->reg);
+}
+EXPORT_SYMBOL_GPL(clocksource_mmio_readl_up);
+
+u64 clocksource_mmio_readl_down(struct clocksource *c)
+{
+	return ~(u64)readl_relaxed(to_mmio_clksrc(c)->reg) & c->mask;
+}
+EXPORT_SYMBOL_GPL(clocksource_mmio_readl_down);
+
+u64 clocksource_mmio_readw_up(struct clocksource *c)
+{
+	return (u64)readw_relaxed(to_mmio_clksrc(c)->reg);
+}
+EXPORT_SYMBOL_GPL(clocksource_mmio_readw_up);
+
+u64 clocksource_mmio_readw_down(struct clocksource *c)
+{
+	return ~(u64)readw_relaxed(to_mmio_clksrc(c)->reg) & c->mask;
+}
+EXPORT_SYMBOL_GPL(clocksource_mmio_readw_down);
+
+/**
+ * clocksource_mmio_init - Initialize a simple mmio based clocksource
+ * @base:	Virtual address of the clock readout register
+ * @name:	Name of the clocksource
+ * @hz:		Frequency of the clocksource in Hz
+ * @rating:	Rating of the clocksource
+ * @bits:	Number of valid bits
+ * @read:	One of clocksource_mmio_read*() above
+ */
+int clocksource_mmio_init(void __iomem *base, const char *name,
+			  unsigned long hz, int rating, unsigned bits,
+			  u64 (*read)(struct clocksource *))
+{
+	struct clocksource_mmio *cs;
+
+	if (bits > 64 || bits < 16)
+		return -EINVAL;
+
+	cs = kzalloc_obj(struct clocksource_mmio);
+	if (!cs)
+		return -ENOMEM;
+
+	cs->reg = base;
+	cs->clksrc.name = name;
+	cs->clksrc.rating = rating;
+	cs->clksrc.read = read;
+	cs->clksrc.mask = CLOCKSOURCE_MASK(bits);
+	cs->clksrc.flags = CLOCK_SOURCE_IS_CONTINUOUS;
+
+	return clocksource_register_hz(&cs->clksrc, hz);
+}
+EXPORT_SYMBOL_GPL(clocksource_mmio_init);