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, 136 insertions, 0 deletions

diff --git a/fs/ext4/symlink.c b/fs/ext4/symlink.c
new file mode 100644
index 000000000..b61226271
--- /dev/null
+++ b/fs/ext4/symlink.c
@@ -0,0 +1,136 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  linux/fs/ext4/symlink.c
+ *
+ * Only fast symlinks left here - the rest is done by generic code. AV, 1999
+ *
+ * Copyright (C) 1992, 1993, 1994, 1995
+ * Remy Card (card@masi.ibp.fr)
+ * Laboratoire MASI - Institut Blaise Pascal
+ * Universite Pierre et Marie Curie (Paris VI)
+ *
+ *  from
+ *
+ *  linux/fs/minix/symlink.c
+ *
+ *  Copyright (C) 1991, 1992  Linus Torvalds
+ *
+ *  ext4 symlink handling code
+ */
+
+#include <linux/fs.h>
+#include <linux/namei.h>
+#include "ext4.h"
+#include "xattr.h"
+
+static const char *ext4_encrypted_get_link(struct dentry *dentry,
+					   struct inode *inode,
+					   struct delayed_call *done)
+{
+	struct buffer_head *bh = NULL;
+	const void *caddr;
+	unsigned int max_size;
+	const char *paddr;
+
+	if (!dentry)
+		return ERR_PTR(-ECHILD);
+
+	if (ext4_inode_is_fast_symlink(inode)) {
+		caddr = EXT4_I(inode)->i_data;
+		max_size = sizeof(EXT4_I(inode)->i_data);
+	} else {
+		bh = ext4_bread(NULL, inode, 0, 0);
+		if (IS_ERR(bh))
+			return ERR_CAST(bh);
+		if (!bh) {
+			EXT4_ERROR_INODE(inode, "bad symlink.");
+			return ERR_PTR(-EFSCORRUPTED);
+		}
+		caddr = bh->b_data;
+		max_size = inode->i_sb->s_blocksize;
+	}
+
+	paddr = fscrypt_get_symlink(inode, caddr, max_size, done);
+	brelse(bh);
+	return paddr;
+}
+
+static int ext4_encrypted_symlink_getattr(struct mnt_idmap *idmap,
+					  const struct path *path,
+					  struct kstat *stat, u32 request_mask,
+					  unsigned int query_flags)
+{
+	ext4_getattr(idmap, path, stat, request_mask, query_flags);
+
+	return fscrypt_symlink_getattr(path, stat);
+}
+
+static void ext4_free_link(void *bh)
+{
+	brelse(bh);
+}
+
+static const char *ext4_get_link(struct dentry *dentry, struct inode *inode,
+				 struct delayed_call *callback)
+{
+	struct buffer_head *bh;
+	char *inline_link;
+
+	/*
+	 * Create a new inlined symlink is not supported, just provide a
+	 * method to read the leftovers.
+	 */
+	if (ext4_has_inline_data(inode)) {
+		if (!dentry)
+			return ERR_PTR(-ECHILD);
+
+		inline_link = ext4_read_inline_link(inode);
+		if (!IS_ERR(inline_link))
+			set_delayed_call(callback, kfree_link, inline_link);
+		return inline_link;
+	}
+
+	if (!dentry) {
+		bh = ext4_getblk(NULL, inode, 0, EXT4_GET_BLOCKS_CACHED_NOWAIT);
+		if (IS_ERR_OR_NULL(bh))
+			return ERR_PTR(-ECHILD);
+		if (!ext4_buffer_uptodate(bh)) {
+			brelse(bh);
+			return ERR_PTR(-ECHILD);
+		}
+	} else {
+		bh = ext4_bread(NULL, inode, 0, 0);
+		if (IS_ERR(bh))
+			return ERR_CAST(bh);
+		if (!bh) {
+			EXT4_ERROR_INODE(inode, "bad symlink.");
+			return ERR_PTR(-EFSCORRUPTED);
+		}
+	}
+
+	set_delayed_call(callback, ext4_free_link, bh);
+	nd_terminate_link(bh->b_data, inode->i_size,
+			  inode->i_sb->s_blocksize - 1);
+	return bh->b_data;
+}
+
+const struct inode_operations ext4_encrypted_symlink_inode_operations = {
+	.get_link	= ext4_encrypted_get_link,
+	.setattr	= ext4_setattr,
+	.getattr	= ext4_encrypted_symlink_getattr,
+	.listxattr	= ext4_listxattr,
+};
+
+const struct inode_operations ext4_symlink_inode_operations = {
+	.get_link	= ext4_get_link,
+	.setattr	= ext4_setattr,
+	.getattr	= ext4_getattr,
+	.listxattr	= ext4_listxattr,
+};
+
+const struct inode_operations ext4_fast_symlink_inode_operations = {
+	.get_link	= simple_get_link,
+	.setattr	= ext4_setattr,
+	.getattr	= ext4_getattr,
+	.listxattr	= ext4_listxattr,
+};