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, 76 insertions, 0 deletions

diff --git a/fs/stack.c b/fs/stack.c
new file mode 100644
index 000000000..d8c782e06
--- /dev/null
+++ b/fs/stack.c
@@ -0,0 +1,76 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/export.h>
+#include <linux/fs.h>
+#include <linux/fs_stack.h>
+
+/* does _NOT_ require i_rwsem to be held.
+ *
+ * This function cannot be inlined since i_size_{read,write} is rather
+ * heavy-weight on 32-bit systems
+ */
+void fsstack_copy_inode_size(struct inode *dst, struct inode *src)
+{
+	loff_t i_size;
+	blkcnt_t i_blocks;
+
+	/*
+	 * i_size_read() includes its own seqlocking and protection from
+	 * preemption (see include/linux/fs.h): we need nothing extra for
+	 * that here, and prefer to avoid nesting locks than attempt to keep
+	 * i_size and i_blocks in sync together.
+	 */
+	i_size = i_size_read(src);
+
+	/*
+	 * But on 32-bit, we ought to make an effort to keep the two halves of
+	 * i_blocks in sync despite SMP or PREEMPTION - though stat's
+	 * generic_fillattr() doesn't bother, and we won't be applying quotas
+	 * (where i_blocks does become important) at the upper level.
+	 *
+	 * We don't actually know what locking is used at the lower level;
+	 * but if it's a filesystem that supports quotas, it will be using
+	 * i_lock as in inode_add_bytes().
+	 */
+	if (sizeof(i_blocks) > sizeof(long))
+		spin_lock(&src->i_lock);
+	i_blocks = src->i_blocks;
+	if (sizeof(i_blocks) > sizeof(long))
+		spin_unlock(&src->i_lock);
+
+	/*
+	 * If CONFIG_SMP or CONFIG_PREEMPTION on 32-bit, it's vital for
+	 * fsstack_copy_inode_size() to hold some lock around
+	 * i_size_write(), otherwise i_size_read() may spin forever (see
+	 * include/linux/fs.h).  We don't necessarily hold i_rwsem when this
+	 * is called, so take i_lock for that case.
+	 *
+	 * And if on 32-bit, continue our effort to keep the two halves of
+	 * i_blocks in sync despite SMP or PREEMPTION: use i_lock for that case
+	 * too, and do both at once by combining the tests.
+	 *
+	 * There is none of this locking overhead in the 64-bit case.
+	 */
+	if (sizeof(i_size) > sizeof(long) || sizeof(i_blocks) > sizeof(long))
+		spin_lock(&dst->i_lock);
+	i_size_write(dst, i_size);
+	dst->i_blocks = i_blocks;
+	if (sizeof(i_size) > sizeof(long) || sizeof(i_blocks) > sizeof(long))
+		spin_unlock(&dst->i_lock);
+}
+EXPORT_SYMBOL_GPL(fsstack_copy_inode_size);
+
+/* copy all attributes */
+void fsstack_copy_attr_all(struct inode *dest, const struct inode *src)
+{
+	dest->i_mode = src->i_mode;
+	dest->i_uid = src->i_uid;
+	dest->i_gid = src->i_gid;
+	dest->i_rdev = src->i_rdev;
+	inode_set_atime_to_ts(dest, inode_get_atime(src));
+	inode_set_mtime_to_ts(dest, inode_get_mtime(src));
+	inode_set_ctime_to_ts(dest, inode_get_ctime(src));
+	dest->i_blkbits = src->i_blkbits;
+	dest->i_flags = src->i_flags;
+	set_nlink(dest, src->i_nlink);
+}
+EXPORT_SYMBOL_GPL(fsstack_copy_attr_all);