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, 109 insertions, 0 deletions

diff --git a/fs/squashfs/symlink.c b/fs/squashfs/symlink.c
new file mode 100644
index 000000000..6ef735bd8
--- /dev/null
+++ b/fs/squashfs/symlink.c
@@ -0,0 +1,109 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Squashfs - a compressed read only filesystem for Linux
+ *
+ * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
+ * Phillip Lougher <phillip@squashfs.org.uk>
+ *
+ * symlink.c
+ */
+
+/*
+ * This file implements code to handle symbolic links.
+ *
+ * The data contents of symbolic links are stored inside the symbolic
+ * link inode within the inode table.  This allows the normally small symbolic
+ * link to be compressed as part of the inode table, achieving much greater
+ * compression than if the symbolic link was compressed individually.
+ */
+
+#include <linux/fs.h>
+#include <linux/vfs.h>
+#include <linux/kernel.h>
+#include <linux/string.h>
+#include <linux/pagemap.h>
+#include <linux/xattr.h>
+
+#include "squashfs_fs.h"
+#include "squashfs_fs_sb.h"
+#include "squashfs_fs_i.h"
+#include "squashfs.h"
+#include "xattr.h"
+
+static int squashfs_symlink_read_folio(struct file *file, struct folio *folio)
+{
+	struct inode *inode = folio->mapping->host;
+	struct super_block *sb = inode->i_sb;
+	struct squashfs_sb_info *msblk = sb->s_fs_info;
+	int index = folio_pos(folio);
+	u64 block = squashfs_i(inode)->start;
+	int offset = squashfs_i(inode)->offset;
+	int length = min_t(int, i_size_read(inode) - index, PAGE_SIZE);
+	int bytes, copied, error;
+	void *pageaddr;
+	struct squashfs_cache_entry *entry;
+
+	TRACE("Entered squashfs_symlink_readpage, page index %ld, start block "
+			"%llx, offset %x\n", folio->index, block, offset);
+
+	/*
+	 * Skip index bytes into symlink metadata.
+	 */
+	if (index) {
+		bytes = squashfs_read_metadata(sb, NULL, &block, &offset,
+								index);
+		if (bytes < 0) {
+			ERROR("Unable to read symlink [%llx:%x]\n",
+				squashfs_i(inode)->start,
+				squashfs_i(inode)->offset);
+			error = bytes;
+			goto out;
+		}
+	}
+
+	/*
+	 * Read length bytes from symlink metadata.  Squashfs_read_metadata
+	 * is not used here because it can sleep and we want to use
+	 * kmap_local to map the folio.  Instead call the underlying
+	 * squashfs_cache_get routine.  As length bytes may overlap metadata
+	 * blocks, we may need to call squashfs_cache_get multiple times.
+	 */
+	for (bytes = 0; bytes < length; offset = 0, bytes += copied) {
+		entry = squashfs_cache_get(sb, msblk->block_cache, block, 0);
+		if (entry->error) {
+			ERROR("Unable to read symlink [%llx:%x]\n",
+				squashfs_i(inode)->start,
+				squashfs_i(inode)->offset);
+			squashfs_cache_put(entry);
+			error = entry->error;
+			goto out;
+		}
+
+		pageaddr = kmap_local_folio(folio, 0);
+		copied = squashfs_copy_data(pageaddr + bytes, entry, offset,
+								length - bytes);
+		if (copied == length - bytes)
+			memset(pageaddr + length, 0, PAGE_SIZE - length);
+		else
+			block = entry->next_index;
+		kunmap_local(pageaddr);
+		squashfs_cache_put(entry);
+	}
+
+	flush_dcache_folio(folio);
+	error = 0;
+out:
+	folio_end_read(folio, error == 0);
+	return error;
+}
+
+
+const struct address_space_operations squashfs_symlink_aops = {
+	.read_folio = squashfs_symlink_read_folio
+};
+
+const struct inode_operations squashfs_symlink_inode_ops = {
+	.get_link = page_get_link,
+	.listxattr = squashfs_listxattr
+};
+