@@ -22,6 +22,9 @@
#include <linux/slab.h>
#include <linux/atomic.h>
#include <linux/device.h>
+#include <linux/srcu.h>
+
+#include "internal.h"
static ssize_t default_read_file(struct file *file, char __user *buf,
size_t count, loff_t *ppos)
@@ -35,13 +38,99 @@ static ssize_t default_write_file(struct file *file, const char __user *buf,
return count;
}
-const struct file_operations debugfs_file_operations = {
+const struct file_operations debugfs_noop_file_operations = {
.read = default_read_file,
.write = default_write_file,
.open = simple_open,
.llseek = noop_llseek,
};
+/**
+ * debugfs_use_file_start - mark the beginning of file data access
+ * @dentry: the dentry object whose data is being accessed.
+ * @srcu_idx: a pointer to some memory to store a SRCU index in.
+ *
+ * Up to a matching call to debugfs_use_file_finish(), any
+ * successive call into the file removing functions debugfs_remove()
+ * and debugfs_remove_recursive() will block. Since associated private
+ * file data may only get freed after a successful return of any of
+ * the removal functions, you may safely access it after a successful
+ * call to debugfs_use_file_start() without worrying about
+ * lifetime issues.
+ *
+ * If -%EIO is returned, the file has already been removed and thus,
+ * it is not safe to access any of its data. If, on the other hand,
+ * it is allowed to access the file data, zero is returned.
+ *
+ * Regardless of the return code, any call to
+ * debugfs_use_file_start() must be followed by a matching call
+ * to debugfs_use_file_finish().
+ */
+static int debugfs_use_file_start(const struct dentry *dentry, int *srcu_idx)
+ __acquires(&debugfs_srcu)
+{
+ *srcu_idx = srcu_read_lock(&debugfs_srcu);
+ barrier();
+ if (d_unlinked(dentry))
+ return -EIO;
+ return 0;
+}
+
+/**
+ * debugfs_use_file_finish - mark the end of file data access
+ * @srcu_idx: the SRCU index "created" by a former call to
+ * debugfs_use_file_start().
+ *
+ * Allow any ongoing concurrent call into debugfs_remove() or
+ * debugfs_remove_recursive() blocked by a former call to
+ * debugfs_use_file_start() to proceed and return to its caller.
+ */
+static void debugfs_use_file_finish(int srcu_idx) __releases(&debugfs_srcu)
+{
+ srcu_read_unlock(&debugfs_srcu, srcu_idx);
+}
+
+#define F_DENTRY(filp) ((filp)->f_path.dentry)
+
+#define REAL_FOPS_DEREF(dentry) \
+ ((const struct file_operations *)(dentry)->d_fsdata)
+
+static int open_proxy_open(struct inode *inode, struct file *filp)
+{
+ const struct dentry *dentry = F_DENTRY(filp);
+ const struct file_operations *real_fops = NULL;
+ int srcu_idx, r;
+
+ r = debugfs_use_file_start(dentry, &srcu_idx);
+ if (r) {
+ r = -ENOENT;
+ goto out;
+ }
+
+ real_fops = REAL_FOPS_DEREF(dentry);
+ real_fops = fops_get(real_fops);
+ if (!real_fops) {
+ /* Huh? Module did not clean up after itself at exit? */
+ WARN(1, "debugfs file owner did not clean up at exit: %pd",
+ dentry);
+ r = -ENXIO;
+ goto out;
+ }
+ replace_fops(filp, real_fops);
+
+ if (real_fops->open)
+ r = real_fops->open(inode, filp);
+
+out:
+ fops_put(real_fops);
+ debugfs_use_file_finish(srcu_idx);
+ return r;
+}
+
+const struct file_operations debugfs_open_proxy_file_operations = {
+ .open = open_proxy_open,
+};
+
static struct dentry *debugfs_create_mode(const char *name, umode_t mode,
struct dentry *parent, void *value,
const struct file_operations *fops,
@@ -27,9 +27,14 @@
#include <linux/parser.h>
#include <linux/magic.h>
#include <linux/slab.h>
+#include <linux/srcu.h>
+
+#include "internal.h"
#define DEBUGFS_DEFAULT_MODE 0700
+DEFINE_SRCU(debugfs_srcu);
+
static struct vfsmount *debugfs_mount;
static int debugfs_mount_count;
static bool debugfs_registered;
@@ -345,8 +350,12 @@ struct dentry *debugfs_create_file(const char *name, umode_t mode,
return failed_creating(dentry);
inode->i_mode = mode;
- inode->i_fop = fops ? fops : &debugfs_file_operations;
inode->i_private = data;
+
+ inode->i_fop = fops ? &debugfs_open_proxy_file_operations
+ : &debugfs_noop_file_operations;
+ dentry->d_fsdata = (void *)fops;
+
d_instantiate(dentry, inode);
fsnotify_create(d_inode(dentry->d_parent), dentry);
return end_creating(dentry);
@@ -570,6 +579,7 @@ void debugfs_remove(struct dentry *dentry)
mutex_unlock(&d_inode(parent)->i_mutex);
if (!ret)
simple_release_fs(&debugfs_mount, &debugfs_mount_count);
+ synchronize_srcu(&debugfs_srcu);
}
EXPORT_SYMBOL_GPL(debugfs_remove);
@@ -647,6 +657,7 @@ void debugfs_remove_recursive(struct dentry *dentry)
if (!__debugfs_remove(child, parent))
simple_release_fs(&debugfs_mount, &debugfs_mount_count);
mutex_unlock(&d_inode(parent)->i_mutex);
+ synchronize_srcu(&debugfs_srcu);
}
EXPORT_SYMBOL_GPL(debugfs_remove_recursive);
new file mode 100644
@@ -0,0 +1,24 @@
+/*
+ * internal.h - declarations internal to debugfs
+ *
+ * Copyright (C) 2016 Nicolai Stange <nicstange@gmail.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License version
+ * 2 as published by the Free Software Foundation.
+ *
+ */
+
+#ifndef _DEBUGFS_INTERNAL_H_
+#define _DEBUGFS_INTERNAL_H_
+
+struct file_operations;
+struct srcu_struct;
+
+/* declared over in file.c */
+extern const struct file_operations debugfs_noop_file_operations;
+extern const struct file_operations debugfs_open_proxy_file_operations;
+
+extern struct srcu_struct debugfs_srcu;
+
+#endif /* _DEBUGFS_INTERNAL_H_ */
@@ -43,9 +43,6 @@ extern struct dentry *arch_debugfs_dir;
#if defined(CONFIG_DEBUG_FS)
-/* declared over in file.c */
-extern const struct file_operations debugfs_file_operations;
-
struct dentry *debugfs_create_file(const char *name, umode_t mode,
struct dentry *parent, void *data,
const struct file_operations *fops);
@@ -257,6 +257,7 @@ config PAGE_OWNER
config DEBUG_FS
bool "Debug Filesystem"
+ select SRCU
help
debugfs is a virtual file system that kernel developers use to put
debugging files into. Enable this option to be able to read and