[PATCH v3 6/8] debugfs: purge obsolete SRCU based removal protection

Nicolai Stange
2017-10-30T23:15:52Z

Purge the SRCU based file removal race protection in favour of the new,
refcount based debugfs_file_get()/debugfs_file_put() API.

Fixes: 49d200deaa68 ("debugfs: prevent access to removed files' private
data")
Signed-off-by: Nicolai Stange <nicstange@gmail.com>
---
fs/debugfs/file.c | 48 ------------------------------------------------
fs/debugfs/inode.c | 7 -------
include/linux/debugfs.h | 19 -------------------
lib/Kconfig.debug | 1 -
4 files changed, 75 deletions(-)

diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index d3a972b45ff0..53f5c9a2af88 100644
--- a/fs/debugfs/file.c
+++ b/fs/debugfs/file.c
@@ -22,7 +22,6 @@
#include <linux/slab.h>
#include <linux/atomic.h>
#include <linux/device.h>
-#include <linux/srcu.h>
#include <asm/poll.h>

#include "internal.h"
@@ -48,53 +47,6 @@ const struct file_operations debugfs_noop_file_operations = {
.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().
- */
-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;
-}
-EXPORT_SYMBOL_GPL(debugfs_use_file_start);
-
-/**
- * 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.
- */
-void debugfs_use_file_finish(int srcu_idx) __releases(&debugfs_srcu)
-{
- srcu_read_unlock(&debugfs_srcu, srcu_idx);
-}
-EXPORT_SYMBOL_GPL(debugfs_use_file_finish);
-
#define F_DENTRY(filp) ((filp)->f_path.dentry)

const struct file_operations *debugfs_real_fops(const struct file *filp)
diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
index 6449eb935540..f587aded46b5 100644
--- a/fs/debugfs/inode.c
+++ b/fs/debugfs/inode.c
@@ -27,14 +27,11 @@
#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;
@@ -693,8 +690,6 @@ void debugfs_remove(struct dentry *dentry)
inode_unlock(d_inode(parent));
if (!ret)
simple_release_fs(&debugfs_mount, &debugfs_mount_count);
-
- synchronize_srcu(&debugfs_srcu);
}
EXPORT_SYMBOL_GPL(debugfs_remove);

@@ -768,8 +763,6 @@ void debugfs_remove_recursive(struct dentry *dentry)
if (!__debugfs_remove(child, parent))
simple_release_fs(&debugfs_mount, &debugfs_mount_count);
inode_unlock(d_inode(parent));
-
- synchronize_srcu(&debugfs_srcu);
}
EXPORT_SYMBOL_GPL(debugfs_remove_recursive);

diff --git a/include/linux/debugfs.h b/include/linux/debugfs.h
index c5eda259b9d6..9f821a43bb0d 100644
--- a/include/linux/debugfs.h
+++ b/include/linux/debugfs.h
@@ -23,7 +23,6 @@

struct device;
struct file_operations;
-struct srcu_struct;

struct debugfs_blob_wrapper {
void *data;
@@ -43,8 +42,6 @@ struct debugfs_regset32 {

extern struct dentry *arch_debugfs_dir;

-extern struct srcu_struct debugfs_srcu;
-
#define DEFINE_DEBUGFS_ATTRIBUTE(__fops, __get, __set, __fmt) \
static int __fops ## _open(struct inode *inode, struct file *file) \
{ \
@@ -90,11 +87,6 @@ struct dentry *debugfs_create_automount(const char *name,
void debugfs_remove(struct dentry *dentry);
void debugfs_remove_recursive(struct dentry *dentry);

-int debugfs_use_file_start(const struct dentry *dentry, int *srcu_idx)
- __acquires(&debugfs_srcu);
-
-void debugfs_use_file_finish(int srcu_idx) __releases(&debugfs_srcu);
-
const struct file_operations *debugfs_real_fops(const struct file *filp);

int debugfs_file_get(struct dentry *dentry);
@@ -227,17 +219,6 @@ static inline void debugfs_remove(struct dentry *dentry)
static inline void debugfs_remove_recursive(struct dentry *dentry)
{ }

-static inline int debugfs_use_file_start(const struct dentry *dentry,
- int *srcu_idx)
- __acquires(&debugfs_srcu)
-{
- return 0;
-}
-
-static inline void debugfs_use_file_finish(int srcu_idx)
- __releases(&debugfs_srcu)
-{ }
-
static inline int debugfs_file_get(struct dentry *dentry)
{
return 0;
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 03e2ac7cceb6..f6140d5a50f1 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -326,7 +326,6 @@ 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
--
2.13.6