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, 144 insertions, 0 deletions

diff --git a/drivers/misc/cb710/sgbuf2.c b/drivers/misc/cb710/sgbuf2.c
new file mode 100644
index 000000000..a798fad5f
--- /dev/null
+++ b/drivers/misc/cb710/sgbuf2.c
@@ -0,0 +1,144 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  cb710/sgbuf2.c
+ *
+ *  Copyright by Michał Mirosław, 2008-2009
+ */
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/cb710.h>
+
+static bool sg_dwiter_next(struct sg_mapping_iter *miter)
+{
+	if (sg_miter_next(miter)) {
+		miter->consumed = 0;
+		return true;
+	} else
+		return false;
+}
+
+static bool sg_dwiter_is_at_end(struct sg_mapping_iter *miter)
+{
+	return miter->length == miter->consumed && !sg_dwiter_next(miter);
+}
+
+static uint32_t sg_dwiter_read_buffer(struct sg_mapping_iter *miter)
+{
+	size_t len, left = 4;
+	uint32_t data;
+	void *addr = &data;
+
+	do {
+		len = min(miter->length - miter->consumed, left);
+		memcpy(addr, miter->addr + miter->consumed, len);
+		miter->consumed += len;
+		left -= len;
+		if (!left)
+			return data;
+		addr += len;
+	} while (sg_dwiter_next(miter));
+
+	memset(addr, 0, left);
+	return data;
+}
+
+static inline bool needs_unaligned_copy(const void *ptr)
+{
+#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
+	return false;
+#else
+	return ((uintptr_t)ptr & 3) != 0;
+#endif
+}
+
+static bool sg_dwiter_get_next_block(struct sg_mapping_iter *miter, uint32_t **ptr)
+{
+	size_t len;
+
+	if (sg_dwiter_is_at_end(miter))
+		return true;
+
+	len = miter->length - miter->consumed;
+
+	if (likely(len >= 4 && !needs_unaligned_copy(
+			miter->addr + miter->consumed))) {
+		*ptr = miter->addr + miter->consumed;
+		miter->consumed += 4;
+		return true;
+	}
+
+	return false;
+}
+
+/**
+ * cb710_sg_dwiter_read_next_block() - get next 32-bit word from sg buffer
+ * @miter: sg mapping iterator used for reading
+ *
+ * Description:
+ *   Returns 32-bit word starting at byte pointed to by @miter@
+ *   handling any alignment issues.  Bytes past the buffer's end
+ *   are not accessed (read) but are returned as zeroes.  @miter@
+ *   is advanced by 4 bytes or to the end of buffer whichever is
+ *   closer.
+ *
+ * Context:
+ *   Same requirements as in sg_miter_next().
+ *
+ * Returns:
+ *   32-bit word just read.
+ */
+uint32_t cb710_sg_dwiter_read_next_block(struct sg_mapping_iter *miter)
+{
+	uint32_t *ptr = NULL;
+
+	if (likely(sg_dwiter_get_next_block(miter, &ptr)))
+		return ptr ? *ptr : 0;
+
+	return sg_dwiter_read_buffer(miter);
+}
+EXPORT_SYMBOL_GPL(cb710_sg_dwiter_read_next_block);
+
+static void sg_dwiter_write_slow(struct sg_mapping_iter *miter, uint32_t data)
+{
+	size_t len, left = 4;
+	void *addr = &data;
+
+	do {
+		len = min(miter->length - miter->consumed, left);
+		memcpy(miter->addr, addr, len);
+		miter->consumed += len;
+		left -= len;
+		if (!left)
+			return;
+		addr += len;
+	} while (sg_dwiter_next(miter));
+}
+
+/**
+ * cb710_sg_dwiter_write_next_block() - write next 32-bit word to sg buffer
+ * @miter: sg mapping iterator used for writing
+ * @data: data to write to sg buffer
+ *
+ * Description:
+ *   Writes 32-bit word starting at byte pointed to by @miter@
+ *   handling any alignment issues.  Bytes which would be written
+ *   past the buffer's end are silently discarded. @miter@ is
+ *   advanced by 4 bytes or to the end of buffer whichever is closer.
+ *
+ * Context:
+ *   Same requirements as in sg_miter_next().
+ */
+void cb710_sg_dwiter_write_next_block(struct sg_mapping_iter *miter, uint32_t data)
+{
+	uint32_t *ptr = NULL;
+
+	if (likely(sg_dwiter_get_next_block(miter, &ptr))) {
+		if (ptr)
+			*ptr = data;
+		else
+			return;
+	} else
+		sg_dwiter_write_slow(miter, data);
+}
+EXPORT_SYMBOL_GPL(cb710_sg_dwiter_write_next_block);
+