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, 204 insertions, 0 deletions

diff --git a/fs/nfs/io.c b/fs/nfs/io.c
new file mode 100644
index 000000000..2faf2003f
--- /dev/null
+++ b/fs/nfs/io.c
@@ -0,0 +1,204 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2016 Trond Myklebust
+ *
+ * I/O and data path helper functionality.
+ */
+
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/bitops.h>
+#include <linux/rwsem.h>
+#include <linux/fs.h>
+#include <linux/nfs_fs.h>
+
+#include "internal.h"
+
+/**
+ * nfs_start_io_read - declare the file is being used for buffered reads
+ * @inode: file inode
+ *
+ * Declare that a buffered read operation is about to start, and ensure
+ * that we block all direct I/O.
+ * On exit, the function ensures that the NFS_INO_ODIRECT flag is unset,
+ * and holds a shared lock on inode->i_rwsem to ensure that the flag
+ * cannot be changed.
+ * In practice, this means that buffered read operations are allowed to
+ * execute in parallel, thanks to the shared lock, whereas direct I/O
+ * operations need to wait to grab an exclusive lock in order to set
+ * NFS_INO_ODIRECT.
+ * Note that buffered writes and truncates both take a write lock on
+ * inode->i_rwsem, meaning that those are serialised w.r.t. the reads.
+ */
+int
+nfs_start_io_read(struct inode *inode)
+{
+	struct nfs_inode *nfsi = NFS_I(inode);
+	int err;
+
+	/* Be an optimist! */
+	err = down_read_killable(&inode->i_rwsem);
+	if (err)
+		return err;
+	if (test_bit(NFS_INO_ODIRECT, &nfsi->flags) == 0)
+		return 0;
+	up_read(&inode->i_rwsem);
+
+	/* Slow path.... */
+	err = down_write_killable(&inode->i_rwsem);
+	if (err)
+		return err;
+	nfs_file_block_o_direct(nfsi);
+	downgrade_write(&inode->i_rwsem);
+
+	return 0;
+}
+
+/**
+ * nfs_end_io_read - declare that the buffered read operation is done
+ * @inode: file inode
+ *
+ * Declare that a buffered read operation is done, and release the shared
+ * lock on inode->i_rwsem.
+ */
+void
+nfs_end_io_read(struct inode *inode)
+{
+	up_read(&inode->i_rwsem);
+}
+
+/**
+ * nfs_start_io_write - declare the file is being used for buffered writes
+ * @inode: file inode
+ *
+ * Declare that a buffered read operation is about to start, and ensure
+ * that we block all direct I/O.
+ */
+int
+nfs_start_io_write(struct inode *inode)
+{
+	int err;
+
+	err = down_write_killable(&inode->i_rwsem);
+	if (!err)
+		nfs_file_block_o_direct(NFS_I(inode));
+	return err;
+}
+EXPORT_SYMBOL_GPL(nfs_start_io_write);
+
+/**
+ * nfs_end_io_write - declare that the buffered write operation is done
+ * @inode: file inode
+ *
+ * Declare that a buffered write operation is done, and release the
+ * lock on inode->i_rwsem.
+ */
+void
+nfs_end_io_write(struct inode *inode)
+{
+	up_write(&inode->i_rwsem);
+}
+EXPORT_SYMBOL_GPL(nfs_end_io_write);
+
+/* Call with exclusively locked inode->i_rwsem */
+static void nfs_block_buffered(struct nfs_inode *nfsi, struct inode *inode)
+{
+	if (!test_bit(NFS_INO_ODIRECT, &nfsi->flags)) {
+		set_bit(NFS_INO_ODIRECT, &nfsi->flags);
+		nfs_sync_mapping(inode->i_mapping);
+	}
+}
+
+static int nfs_block_buffered_nowait(struct nfs_inode *nfsi, struct inode *inode)
+{
+	if (!test_bit(NFS_INO_ODIRECT, &nfsi->flags)) {
+		if (inode->i_mapping->nrpages != 0)
+			return 1;
+		set_bit(NFS_INO_ODIRECT, &nfsi->flags);
+	}
+	return 0;
+}
+
+/**
+ * nfs_start_io_direct - declare the file is being used for direct i/o
+ * @inode: file inode
+ *
+ * Declare that a direct I/O operation is about to start, and ensure
+ * that we block all buffered I/O.
+ * On exit, the function ensures that the NFS_INO_ODIRECT flag is set,
+ * and holds a shared lock on inode->i_rwsem to ensure that the flag
+ * cannot be changed.
+ * In practice, this means that direct I/O operations are allowed to
+ * execute in parallel, thanks to the shared lock, whereas buffered I/O
+ * operations need to wait to grab an exclusive lock in order to clear
+ * NFS_INO_ODIRECT.
+ * Note that buffered writes and truncates both take a write lock on
+ * inode->i_rwsem, meaning that those are serialised w.r.t. O_DIRECT.
+ */
+int
+nfs_start_io_direct(struct inode *inode)
+{
+	struct nfs_inode *nfsi = NFS_I(inode);
+	int err;
+
+	/* Be an optimist! */
+	err = down_read_killable(&inode->i_rwsem);
+	if (err)
+		return err;
+	if (test_bit(NFS_INO_ODIRECT, &nfsi->flags) != 0)
+		return 0;
+	up_read(&inode->i_rwsem);
+
+	/* Slow path.... */
+	err = down_write_killable(&inode->i_rwsem);
+	if (err)
+		return err;
+	nfs_block_buffered(nfsi, inode);
+	downgrade_write(&inode->i_rwsem);
+
+	return 0;
+}
+
+/**
+ * nfs_start_io_direct_nowait - non-blocking variant of nfs_start_io_direct()
+ * @inode: file inode
+ *
+ * Try to declare that a direct I/O operation is about to start without
+ * blocking.
+ * Ensure all buffered I/O is blocked.
+ * If this could not be done without blocking then returns -EAGAIN.
+ */
+int
+nfs_start_io_direct_nowait(struct inode *inode)
+{
+	struct nfs_inode *nfsi = NFS_I(inode);
+
+	if (!down_read_trylock(&inode->i_rwsem))
+		return -EAGAIN;
+	if (test_bit(NFS_INO_ODIRECT, &nfsi->flags))
+		return 0;
+	up_read(&inode->i_rwsem);
+
+	/* Slow path: try to flip NFS_INO_ODIRECT without blocking. */
+	if (!down_write_trylock(&inode->i_rwsem))
+		return -EAGAIN;
+	if (nfs_block_buffered_nowait(nfsi, inode)) {
+		up_write(&inode->i_rwsem);
+		return -EAGAIN;
+	}
+	downgrade_write(&inode->i_rwsem);
+	return 0;
+}
+
+/**
+ * nfs_end_io_direct - declare that the direct i/o operation is done
+ * @inode: file inode
+ *
+ * Declare that a direct I/O operation is done, and release the shared
+ * lock on inode->i_rwsem.
+ */
+void
+nfs_end_io_direct(struct inode *inode)
+{
+	up_read(&inode->i_rwsem);
+}