Hi,
Alan Stern has discovered a race in sysfs, whereby driver callbacks could be
called after sysfs_remove_file() has run. The attached patch should fix it.
It introduces a new data structure acting as a collection of all sysfs_buffers
associated with an attribute. Upon removal of an attribute the buffers are
marked orphaned and IO on them returns -ENODEV. Thus sysfs_remove_file()
makes sure that sysfs won't bother a driver after that call, making it safe
to free the associated data structures and to unload the driver.
Regards
Oliver
--- linux-2.6.19-rc6/fs/sysfs/file.c 2006-11-25 23:49:07.000000000 +0100
+++ sysfs/fs/sysfs/file.c 2006-12-01 09:47:24.000000000 +0100
@@ -7,6 +7,7 @@
#include <linux/kobject.h>
#include <linux/namei.h>
#include <linux/poll.h>
+#include <linux/list.h>
#include <asm/uaccess.h>
#include <asm/semaphore.h>
@@ -50,17 +51,29 @@
.store = subsys_attr_store,
};
+/**
+ * add_to_collection - add buffer to a collection
+ * @buffer: buffer to be added
+ * @node inode of set to add to
+ */
-struct sysfs_buffer {
- size_t count;
- loff_t pos;
- char * page;
- struct sysfs_ops * ops;
- struct semaphore sem;
- int needs_read_fill;
- int event;
-};
+static inline void
+add_to_collection(struct sysfs_buffer *buffer, struct inode *node)
+{
+ struct sysfs_buffer_collection *set = node->i_private;
+
+ mutex_lock(&node->i_mutex);
+ list_add(&buffer->associates, &set->associates);
+ mutex_unlock(&node->i_mutex);
+}
+static inline void
+remove_from_collection(struct sysfs_buffer *buffer, struct inode *node)
+{
+ mutex_lock(&node->i_mutex);
+ list_del(&buffer->associates);
+ mutex_unlock(&node->i_mutex);
+}
/**
* fill_read_buffer - allocate and fill buffer from object.
@@ -153,6 +166,10 @@
ssize_t retval = 0;
down(&buffer->sem);
+ if (buffer->orphaned) {
+ retval = -ENODEV;
+ goto out;
+ }
if (buffer->needs_read_fill) {
if ((retval = fill_read_buffer(file->f_dentry,buffer)))
goto out;
@@ -165,7 +182,6 @@
return retval;
}
-
/**
* fill_write_buffer - copy buffer from userspace.
* @buffer: data buffer for file.
@@ -240,19 +256,25 @@
ssize_t len;
down(&buffer->sem);
+ if (buffer->orphaned) {
+ len = -ENODEV;
+ goto out;
+ }
len = fill_write_buffer(buffer, buf, count);
if (len > 0)
len = flush_write_buffer(file->f_dentry, buffer, len);
if (len > 0)
*ppos += len;
+out:
up(&buffer->sem);
return len;
}
-static int check_perm(struct inode * inode, struct file * file)
+static int sysfs_open_file(struct inode * inode, struct file * file)
{
struct kobject *kobj = sysfs_get_kobject(file->f_dentry->d_parent);
struct attribute * attr = to_attr(file->f_dentry);
+ struct sysfs_buffer_collection *set;
struct sysfs_buffer * buffer;
struct sysfs_ops * ops = NULL;
int error = 0;
@@ -282,6 +304,18 @@
if (!ops)
goto Eaccess;
+ /* make sure we have a collection to add our buffers to */
+ mutex_lock(&inode->i_mutex);
+ if (!(set = inode->i_private)) {
+ if (!(set = inode->i_private = kmalloc(sizeof(struct sysfs_buffer_collection), GFP_KERNEL))) {
+ error = -ENOMEM;
+ goto Done;
+ } else {
+ INIT_LIST_HEAD(&set->associates);
+ }
+ }
+ mutex_unlock(&inode->i_mutex);
+
/* File needs write support.
* The inode's perms must say it's ok,
* and we must have a store method.
@@ -307,9 +341,11 @@
*/
buffer = kzalloc(sizeof(struct sysfs_buffer), GFP_KERNEL);
if (buffer) {
+ INIT_LIST_HEAD(&buffer->associates);
init_MUTEX(&buffer->sem);
buffer->needs_read_fill = 1;
buffer->ops = ops;
+ add_to_collection(buffer, inode);
file->private_data = buffer;
} else
error = -ENOMEM;
@@ -327,11 +363,6 @@
return error;
}
-static int sysfs_open_file(struct inode * inode, struct file * filp)
-{
- return check_perm(inode,filp);
-}
-
static int sysfs_release(struct inode * inode, struct file * filp)
{
struct kobject * kobj = to_kobj(filp->f_dentry->d_parent);
@@ -339,6 +370,8 @@
struct module * owner = attr->owner;
struct sysfs_buffer * buffer = filp->private_data;
+ if (buffer)
+ remove_from_collection(buffer, inode);
if (kobj)
kobject_put(kobj);
/* After this point, attr should not be accessed. */
@@ -545,7 +578,9 @@
void sysfs_remove_file(struct kobject * kobj, const struct attribute * attr)
{
- sysfs_hash_and_remove(kobj->dentry,attr->name);
+ struct dentry *d = kobj->dentry;
+
+ sysfs_hash_and_remove(d, attr->name);
}
--- linux-2.6.19-rc6/fs/sysfs/sysfs.h 2006-11-16 05:03:40.000000000 +0100
+++ sysfs/fs/sysfs/sysfs.h 2006-12-01 09:47:44.000000000 +0100
@@ -33,6 +33,22 @@
struct kobject * target_kobj;
};
+struct sysfs_buffer {
+ struct list_head associates;
+ size_t count;
+ loff_t pos;
+ char * page;
+ struct sysfs_ops * ops;
+ struct semaphore sem;
+ int orphaned;
+ int needs_read_fill;
+ int event;
+};
+
+struct sysfs_buffer_collection {
+ struct list_head associates;
+};
+
static inline struct kobject * to_kobj(struct dentry * dentry)
{
struct sysfs_dirent * sd = dentry->d_fsdata;
@@ -95,4 +111,3 @@
if (atomic_dec_and_test(&sd->s_count))
release_sysfs_dirent(sd);
}
-
--- linux-2.6.19-rc6/fs/sysfs/mount.c 2006-11-16 05:03:40.000000000 +0100
+++ sysfs/fs/sysfs/mount.c 2006-11-26 14:00:13.000000000 +0100
@@ -18,9 +18,12 @@
struct super_block * sysfs_sb = NULL;
kmem_cache_t *sysfs_dir_cachep;
+static void sysfs_clear_inode(struct inode *inode);
+
static struct super_operations sysfs_ops = {
.statfs = simple_statfs,
.drop_inode = generic_delete_inode,
+ .clear_inode = sysfs_clear_inode,
};
static struct sysfs_dirent sysfs_root = {
@@ -31,6 +34,11 @@
.s_iattr = NULL,
};
+static void sysfs_clear_inode(struct inode *inode)
+{
+ kfree(inode->i_private);
+}
+
static int sysfs_fill_super(struct super_block *sb, void *data, int silent)
{
struct inode *inode;
--- linux-2.6.19-rc6/fs/sysfs/inode.c 2006-11-16 05:03:40.000000000 +0100
+++ sysfs/fs/sysfs/inode.c 2006-12-01 09:48:11.000000000 +0100
@@ -209,6 +209,22 @@
return NULL;
}
+static inline void orphan_all_buffers(struct inode *node)
+{
+ struct sysfs_buffer_collection *set = node->i_private;
+ struct sysfs_buffer *buf;
+
+ mutex_lock(&node->i_mutex);
+ if (node->i_private) {
+ list_for_each_entry(buf, &set->associates, associates) {
+ down(&buf->sem);
+ buf->orphaned = 1;
+ up(&buf->sem);
+ }
+ }
+ mutex_unlock(&node->i_mutex);
+}
+
/*
* Unhashes the dentry corresponding to given sysfs_dirent
@@ -217,16 +233,23 @@
void sysfs_drop_dentry(struct sysfs_dirent * sd, struct dentry * parent)
{
struct dentry * dentry = sd->s_dentry;
+ struct inode *inode;
if (dentry) {
spin_lock(&dcache_lock);
spin_lock(&dentry->d_lock);
if (!(d_unhashed(dentry) && dentry->d_inode)) {
+ inode = dentry->d_inode;
+ spin_lock(&inode->i_lock);
+ __iget(inode);
+ spin_unlock(&inode->i_lock);
dget_locked(dentry);
__d_drop(dentry);
spin_unlock(&dentry->d_lock);
spin_unlock(&dcache_lock);
simple_unlink(parent->d_inode, dentry);
+ orphan_all_buffers(inode);
+ iput(inode);
} else {
spin_unlock(&dentry->d_lock);
spin_unlock(&dcache_lock);
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