#include <linux/slab.h>
#include <linux/uaccess.h>
#include <linux/fs_parser.h>
+#include <linux/rculist.h>
/*
- * Handling of filesystem drivers list.
- * Rules:
- * Inclusion to/removals from/scanning of list are protected by spinlock.
- * During the unload module must call unregister_filesystem().
- * We can access the fields of list element if:
- * 1) spinlock is held or
- * 2) we hold the reference to the module.
- * The latter can be guaranteed by call of try_module_get(); if it
- * returned 0 we must skip the element, otherwise we got the reference.
- * Once the reference is obtained we can drop the spinlock.
+ * Read-mostly filesystem drivers list.
+ *
+ * Readers walk under rcu_read_lock(); writers take file_systems_lock
+ * and publish via _rcu hlist primitives. unregister_filesystem()
+ * synchronize_rcu()s after unlock so the embedded file_system_type
+ * can't go away under a reader. To keep using a filesystem after
+ * the RCU section ends, take a module reference via try_module_get().
*/
-
-static struct file_system_type *file_systems;
-static DEFINE_RWLOCK(file_systems_lock);
+static HLIST_HEAD(file_systems);
+static DEFINE_SPINLOCK(file_systems_lock);
/* WARNING: This can be used only if we _already_ own a reference */
struct file_system_type *get_filesystem(struct file_system_type *fs)
module_put(fs->owner);
}
-static struct file_system_type **find_filesystem(const char *name, unsigned len)
+static struct file_system_type *find_filesystem(const char *name, unsigned len)
{
- struct file_system_type **p;
- for (p = &file_systems; *p; p = &(*p)->next)
- if (strncmp((*p)->name, name, len) == 0 &&
- !(*p)->name[len])
- break;
- return p;
+ struct file_system_type *fs;
+
+ hlist_for_each_entry_rcu(fs, &file_systems, list,
+ lockdep_is_held(&file_systems_lock))
+ if (strncmp(fs->name, name, len) == 0 && !fs->name[len])
+ return fs;
+ return NULL;
}
/**
* is aware of for mount and other syscalls. Returns 0 on success,
* or a negative errno code on an error.
*
- * The &struct file_system_type that is passed is linked into the kernel
+ * The &struct file_system_type that is passed is linked into the kernel
* structures and must not be freed until the file system has been
* unregistered.
*/
-
-int register_filesystem(struct file_system_type * fs)
+int register_filesystem(struct file_system_type *fs)
{
- int res = 0;
- struct file_system_type ** p;
-
if (fs->parameters &&
!fs_validate_description(fs->name, fs->parameters))
return -EINVAL;
BUG_ON(strchr(fs->name, '.'));
- if (fs->next)
+ if (!hlist_unhashed_lockless(&fs->list))
return -EBUSY;
- write_lock(&file_systems_lock);
- p = find_filesystem(fs->name, strlen(fs->name));
- if (*p)
- res = -EBUSY;
- else
- *p = fs;
- write_unlock(&file_systems_lock);
- return res;
-}
+ guard(spinlock)(&file_systems_lock);
+ if (find_filesystem(fs->name, strlen(fs->name)))
+ return -EBUSY;
+ hlist_add_tail_rcu(&fs->list, &file_systems);
+ return 0;
+}
EXPORT_SYMBOL(register_filesystem);
/**
* Remove a file system that was previously successfully registered
* with the kernel. An error is returned if the file system is not found.
* Zero is returned on a success.
- *
+ *
* Once this function has returned the &struct file_system_type structure
* may be freed or reused.
*/
-
-int unregister_filesystem(struct file_system_type * fs)
+int unregister_filesystem(struct file_system_type *fs)
{
- struct file_system_type ** tmp;
-
- write_lock(&file_systems_lock);
- tmp = &file_systems;
- while (*tmp) {
- if (fs == *tmp) {
- *tmp = fs->next;
- fs->next = NULL;
- write_unlock(&file_systems_lock);
- synchronize_rcu();
- return 0;
- }
- tmp = &(*tmp)->next;
+ scoped_guard(spinlock, &file_systems_lock) {
+ if (hlist_unhashed(&fs->list))
+ return -EINVAL;
+ hlist_del_init_rcu(&fs->list);
}
- write_unlock(&file_systems_lock);
-
- return -EINVAL;
+ synchronize_rcu();
+ return 0;
}
-
EXPORT_SYMBOL(unregister_filesystem);
#ifdef CONFIG_SYSFS_SYSCALL
-static int fs_index(const char __user * __name)
+static int fs_index(const char __user *__name)
{
- struct file_system_type * tmp;
+ struct file_system_type *p;
char *name __free(kfree) = strndup_user(__name, PATH_MAX);
- int err, index;
+ int index = 0;
if (IS_ERR(name))
return PTR_ERR(name);
- err = -EINVAL;
- read_lock(&file_systems_lock);
- for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) {
- if (strcmp(tmp->name, name) == 0) {
- err = index;
- break;
- }
+ guard(rcu)();
+ hlist_for_each_entry_rcu(p, &file_systems, list) {
+ if (strcmp(p->name, name) == 0)
+ return index;
+ index++;
}
- read_unlock(&file_systems_lock);
- return err;
+ return -EINVAL;
}
-static int fs_name(unsigned int index, char __user * buf)
+static int fs_name(unsigned int index, char __user *buf)
{
- struct file_system_type * tmp;
- int len, res = -EINVAL;
-
- read_lock(&file_systems_lock);
- for (tmp = file_systems; tmp; tmp = tmp->next, index--) {
- if (index == 0) {
- if (try_module_get(tmp->owner))
- res = 0;
+ struct file_system_type *p, *found = NULL;
+ int len, res;
+
+ scoped_guard(rcu) {
+ hlist_for_each_entry_rcu(p, &file_systems, list) {
+ if (index--)
+ continue;
+ if (try_module_get(p->owner))
+ found = p;
break;
}
}
- read_unlock(&file_systems_lock);
- if (res)
- return res;
+ if (!found)
+ return -EINVAL;
/* OK, we got the reference, so we can safely block */
- len = strlen(tmp->name) + 1;
- res = copy_to_user(buf, tmp->name, len) ? -EFAULT : 0;
- put_filesystem(tmp);
+ len = strlen(found->name) + 1;
+ res = copy_to_user(buf, found->name, len) ? -EFAULT : 0;
+ put_filesystem(found);
return res;
}
static int fs_maxindex(void)
{
- struct file_system_type * tmp;
- int index;
+ struct file_system_type *p;
+ int index = 0;
- read_lock(&file_systems_lock);
- for (tmp = file_systems, index = 0 ; tmp ; tmp = tmp->next, index++)
- ;
- read_unlock(&file_systems_lock);
+ guard(rcu)();
+ hlist_for_each_entry_rcu(p, &file_systems, list)
+ index++;
return index;
}
/*
- * Whee.. Weird sysv syscall.
+ * Whee.. Weird sysv syscall.
*/
SYSCALL_DEFINE3(sysfs, int, option, unsigned long, arg1, unsigned long, arg2)
{
size_t len;
int count = 0;
- read_lock(&file_systems_lock);
- for (p = file_systems; p; p = p->next) {
+ guard(rcu)();
+ hlist_for_each_entry_rcu(p, &file_systems, list) {
if (!(p->fs_flags & FS_REQUIRES_DEV))
continue;
len = strlen(p->name) + 1;
size -= len;
count++;
}
- read_unlock(&file_systems_lock);
return count;
}
#ifdef CONFIG_PROC_FS
static int filesystems_proc_show(struct seq_file *m, void *v)
{
- struct file_system_type * tmp;
+ struct file_system_type *p;
- read_lock(&file_systems_lock);
- tmp = file_systems;
- while (tmp) {
+ guard(rcu)();
+ hlist_for_each_entry_rcu(p, &file_systems, list) {
seq_printf(m, "%s\t%s\n",
- (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
- tmp->name);
- tmp = tmp->next;
+ (p->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
+ p->name);
}
- read_unlock(&file_systems_lock);
return 0;
}
{
struct file_system_type *fs;
- read_lock(&file_systems_lock);
- fs = *(find_filesystem(name, len));
+ guard(rcu)();
+ fs = find_filesystem(name, len);
if (fs && !try_module_get(fs->owner))
fs = NULL;
- read_unlock(&file_systems_lock);
return fs;
}
}
return fs;
}
-
EXPORT_SYMBOL(get_fs_type);
projects / thirdparty / linux.git / commitdiff
