Revision 6fc5bae797a6632bbccdd49a1b6a96121368a4b9 authored by David S. Miller on 29 December 2006, 05:00:23 UTC, committed by David S. Miller on 31 December 2006, 22:06:04 UTC
We were not being careful enough. When we trim the physical memory areas, we have to make sure we don't remove the kernel image or initial ramdisk image ranges. Signed-off-by: David S. Miller <davem@davemloft.net>
1 parent bfff6e9
futex.c
/*
* Fast Userspace Mutexes (which I call "Futexes!").
* (C) Rusty Russell, IBM 2002
*
* Generalized futexes, futex requeueing, misc fixes by Ingo Molnar
* (C) Copyright 2003 Red Hat Inc, All Rights Reserved
*
* Removed page pinning, fix privately mapped COW pages and other cleanups
* (C) Copyright 2003, 2004 Jamie Lokier
*
* Robust futex support started by Ingo Molnar
* (C) Copyright 2006 Red Hat Inc, All Rights Reserved
* Thanks to Thomas Gleixner for suggestions, analysis and fixes.
*
* PI-futex support started by Ingo Molnar and Thomas Gleixner
* Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
* Copyright (C) 2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
*
* Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly
* enough at me, Linus for the original (flawed) idea, Matthew
* Kirkwood for proof-of-concept implementation.
*
* "The futexes are also cursed."
* "But they come in a choice of three flavours!"
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
#include <linux/slab.h>
#include <linux/poll.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/jhash.h>
#include <linux/init.h>
#include <linux/futex.h>
#include <linux/mount.h>
#include <linux/pagemap.h>
#include <linux/syscalls.h>
#include <linux/signal.h>
#include <asm/futex.h>
#include "rtmutex_common.h"
#define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8)
/*
* Futexes are matched on equal values of this key.
* The key type depends on whether it's a shared or private mapping.
* Don't rearrange members without looking at hash_futex().
*
* offset is aligned to a multiple of sizeof(u32) (== 4) by definition.
* We set bit 0 to indicate if it's an inode-based key.
*/
union futex_key {
struct {
unsigned long pgoff;
struct inode *inode;
int offset;
} shared;
struct {
unsigned long address;
struct mm_struct *mm;
int offset;
} private;
struct {
unsigned long word;
void *ptr;
int offset;
} both;
};
/*
* Priority Inheritance state:
*/
struct futex_pi_state {
/*
* list of 'owned' pi_state instances - these have to be
* cleaned up in do_exit() if the task exits prematurely:
*/
struct list_head list;
/*
* The PI object:
*/
struct rt_mutex pi_mutex;
struct task_struct *owner;
atomic_t refcount;
union futex_key key;
};
/*
* We use this hashed waitqueue instead of a normal wait_queue_t, so
* we can wake only the relevant ones (hashed queues may be shared).
*
* A futex_q has a woken state, just like tasks have TASK_RUNNING.
* It is considered woken when list_empty(&q->list) || q->lock_ptr == 0.
* The order of wakup is always to make the first condition true, then
* wake up q->waiters, then make the second condition true.
*/
struct futex_q {
struct list_head list;
wait_queue_head_t waiters;
/* Which hash list lock to use: */
spinlock_t *lock_ptr;
/* Key which the futex is hashed on: */
union futex_key key;
/* For fd, sigio sent using these: */
int fd;
struct file *filp;
/* Optional priority inheritance state: */
struct futex_pi_state *pi_state;
struct task_struct *task;
};
/*
* Split the global futex_lock into every hash list lock.
*/
struct futex_hash_bucket {
spinlock_t lock;
struct list_head chain;
};
static struct futex_hash_bucket futex_queues[1<<FUTEX_HASHBITS];
/* Futex-fs vfsmount entry: */
static struct vfsmount *futex_mnt;
/*
* We hash on the keys returned from get_futex_key (see below).
*/
static struct futex_hash_bucket *hash_futex(union futex_key *key)
{
u32 hash = jhash2((u32*)&key->both.word,
(sizeof(key->both.word)+sizeof(key->both.ptr))/4,
key->both.offset);
return &futex_queues[hash & ((1 << FUTEX_HASHBITS)-1)];
}
/*
* Return 1 if two futex_keys are equal, 0 otherwise.
*/
static inline int match_futex(union futex_key *key1, union futex_key *key2)
{
return (key1->both.word == key2->both.word
&& key1->both.ptr == key2->both.ptr
&& key1->both.offset == key2->both.offset);
}
/*
* Get parameters which are the keys for a futex.
*
* For shared mappings, it's (page->index, vma->vm_file->f_path.dentry->d_inode,
* offset_within_page). For private mappings, it's (uaddr, current->mm).
* We can usually work out the index without swapping in the page.
*
* Returns: 0, or negative error code.
* The key words are stored in *key on success.
*
* Should be called with ¤t->mm->mmap_sem but NOT any spinlocks.
*/
static int get_futex_key(u32 __user *uaddr, union futex_key *key)
{
unsigned long address = (unsigned long)uaddr;
struct mm_struct *mm = current->mm;
struct vm_area_struct *vma;
struct page *page;
int err;
/*
* The futex address must be "naturally" aligned.
*/
key->both.offset = address % PAGE_SIZE;
if (unlikely((key->both.offset % sizeof(u32)) != 0))
return -EINVAL;
address -= key->both.offset;
/*
* The futex is hashed differently depending on whether
* it's in a shared or private mapping. So check vma first.
*/
vma = find_extend_vma(mm, address);
if (unlikely(!vma))
return -EFAULT;
/*
* Permissions.
*/
if (unlikely((vma->vm_flags & (VM_IO|VM_READ)) != VM_READ))
return (vma->vm_flags & VM_IO) ? -EPERM : -EACCES;
/*
* Private mappings are handled in a simple way.
*
* NOTE: When userspace waits on a MAP_SHARED mapping, even if
* it's a read-only handle, it's expected that futexes attach to
* the object not the particular process. Therefore we use
* VM_MAYSHARE here, not VM_SHARED which is restricted to shared
* mappings of _writable_ handles.
*/
if (likely(!(vma->vm_flags & VM_MAYSHARE))) {
key->private.mm = mm;
key->private.address = address;
return 0;
}
/*
* Linear file mappings are also simple.
*/
key->shared.inode = vma->vm_file->f_path.dentry->d_inode;
key->both.offset++; /* Bit 0 of offset indicates inode-based key. */
if (likely(!(vma->vm_flags & VM_NONLINEAR))) {
key->shared.pgoff = (((address - vma->vm_start) >> PAGE_SHIFT)
+ vma->vm_pgoff);
return 0;
}
/*
* We could walk the page table to read the non-linear
* pte, and get the page index without fetching the page
* from swap. But that's a lot of code to duplicate here
* for a rare case, so we simply fetch the page.
*/
err = get_user_pages(current, mm, address, 1, 0, 0, &page, NULL);
if (err >= 0) {
key->shared.pgoff =
page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
put_page(page);
return 0;
}
return err;
}
/*
* Take a reference to the resource addressed by a key.
* Can be called while holding spinlocks.
*
* NOTE: mmap_sem MUST be held between get_futex_key() and calling this
* function, if it is called at all. mmap_sem keeps key->shared.inode valid.
*/
static inline void get_key_refs(union futex_key *key)
{
if (key->both.ptr != 0) {
if (key->both.offset & 1)
atomic_inc(&key->shared.inode->i_count);
else
atomic_inc(&key->private.mm->mm_count);
}
}
/*
* Drop a reference to the resource addressed by a key.
* The hash bucket spinlock must not be held.
*/
static void drop_key_refs(union futex_key *key)
{
if (key->both.ptr != 0) {
if (key->both.offset & 1)
iput(key->shared.inode);
else
mmdrop(key->private.mm);
}
}
static inline int get_futex_value_locked(u32 *dest, u32 __user *from)
{
int ret;
pagefault_disable();
ret = __copy_from_user_inatomic(dest, from, sizeof(u32));
pagefault_enable();
return ret ? -EFAULT : 0;
}
/*
* Fault handling. Called with current->mm->mmap_sem held.
*/
static int futex_handle_fault(unsigned long address, int attempt)
{
struct vm_area_struct * vma;
struct mm_struct *mm = current->mm;
if (attempt > 2 || !(vma = find_vma(mm, address)) ||
vma->vm_start > address || !(vma->vm_flags & VM_WRITE))
return -EFAULT;
switch (handle_mm_fault(mm, vma, address, 1)) {
case VM_FAULT_MINOR:
current->min_flt++;
break;
case VM_FAULT_MAJOR:
current->maj_flt++;
break;
default:
return -EFAULT;
}
return 0;
}
/*
* PI code:
*/
static int refill_pi_state_cache(void)
{
struct futex_pi_state *pi_state;
if (likely(current->pi_state_cache))
return 0;
pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
if (!pi_state)
return -ENOMEM;
INIT_LIST_HEAD(&pi_state->list);
/* pi_mutex gets initialized later */
pi_state->owner = NULL;
atomic_set(&pi_state->refcount, 1);
current->pi_state_cache = pi_state;
return 0;
}
static struct futex_pi_state * alloc_pi_state(void)
{
struct futex_pi_state *pi_state = current->pi_state_cache;
WARN_ON(!pi_state);
current->pi_state_cache = NULL;
return pi_state;
}
static void free_pi_state(struct futex_pi_state *pi_state)
{
if (!atomic_dec_and_test(&pi_state->refcount))
return;
/*
* If pi_state->owner is NULL, the owner is most probably dying
* and has cleaned up the pi_state already
*/
if (pi_state->owner) {
spin_lock_irq(&pi_state->owner->pi_lock);
list_del_init(&pi_state->list);
spin_unlock_irq(&pi_state->owner->pi_lock);
rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
}
if (current->pi_state_cache)
kfree(pi_state);
else {
/*
* pi_state->list is already empty.
* clear pi_state->owner.
* refcount is at 0 - put it back to 1.
*/
pi_state->owner = NULL;
atomic_set(&pi_state->refcount, 1);
current->pi_state_cache = pi_state;
}
}
/*
* Look up the task based on what TID userspace gave us.
* We dont trust it.
*/
static struct task_struct * futex_find_get_task(pid_t pid)
{
struct task_struct *p;
rcu_read_lock();
p = find_task_by_pid(pid);
if (!p)
goto out_unlock;
if ((current->euid != p->euid) && (current->euid != p->uid)) {
p = NULL;
goto out_unlock;
}
if (p->exit_state != 0) {
p = NULL;
goto out_unlock;
}
get_task_struct(p);
out_unlock:
rcu_read_unlock();
return p;
}
/*
* This task is holding PI mutexes at exit time => bad.
* Kernel cleans up PI-state, but userspace is likely hosed.
* (Robust-futex cleanup is separate and might save the day for userspace.)
*/
void exit_pi_state_list(struct task_struct *curr)
{
struct list_head *next, *head = &curr->pi_state_list;
struct futex_pi_state *pi_state;
struct futex_hash_bucket *hb;
union futex_key key;
/*
* We are a ZOMBIE and nobody can enqueue itself on
* pi_state_list anymore, but we have to be careful
* versus waiters unqueueing themselves:
*/
spin_lock_irq(&curr->pi_lock);
while (!list_empty(head)) {
next = head->next;
pi_state = list_entry(next, struct futex_pi_state, list);
key = pi_state->key;
hb = hash_futex(&key);
spin_unlock_irq(&curr->pi_lock);
spin_lock(&hb->lock);
spin_lock_irq(&curr->pi_lock);
/*
* We dropped the pi-lock, so re-check whether this
* task still owns the PI-state:
*/
if (head->next != next) {
spin_unlock(&hb->lock);
continue;
}
WARN_ON(pi_state->owner != curr);
WARN_ON(list_empty(&pi_state->list));
list_del_init(&pi_state->list);
pi_state->owner = NULL;
spin_unlock_irq(&curr->pi_lock);
rt_mutex_unlock(&pi_state->pi_mutex);
spin_unlock(&hb->lock);
spin_lock_irq(&curr->pi_lock);
}
spin_unlock_irq(&curr->pi_lock);
}
static int
lookup_pi_state(u32 uval, struct futex_hash_bucket *hb, struct futex_q *me)
{
struct futex_pi_state *pi_state = NULL;
struct futex_q *this, *next;
struct list_head *head;
struct task_struct *p;
pid_t pid;
head = &hb->chain;
list_for_each_entry_safe(this, next, head, list) {
if (match_futex(&this->key, &me->key)) {
/*
* Another waiter already exists - bump up
* the refcount and return its pi_state:
*/
pi_state = this->pi_state;
/*
* Userspace might have messed up non PI and PI futexes
*/
if (unlikely(!pi_state))
return -EINVAL;
WARN_ON(!atomic_read(&pi_state->refcount));
atomic_inc(&pi_state->refcount);
me->pi_state = pi_state;
return 0;
}
}
/*
* We are the first waiter - try to look up the real owner and attach
* the new pi_state to it, but bail out when the owner died bit is set
* and TID = 0:
*/
pid = uval & FUTEX_TID_MASK;
if (!pid && (uval & FUTEX_OWNER_DIED))
return -ESRCH;
p = futex_find_get_task(pid);
if (!p)
return -ESRCH;
pi_state = alloc_pi_state();
/*
* Initialize the pi_mutex in locked state and make 'p'
* the owner of it:
*/
rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
/* Store the key for possible exit cleanups: */
pi_state->key = me->key;
spin_lock_irq(&p->pi_lock);
WARN_ON(!list_empty(&pi_state->list));
list_add(&pi_state->list, &p->pi_state_list);
pi_state->owner = p;
spin_unlock_irq(&p->pi_lock);
put_task_struct(p);
me->pi_state = pi_state;
return 0;
}
/*
* The hash bucket lock must be held when this is called.
* Afterwards, the futex_q must not be accessed.
*/
static void wake_futex(struct futex_q *q)
{
list_del_init(&q->list);
if (q->filp)
send_sigio(&q->filp->f_owner, q->fd, POLL_IN);
/*
* The lock in wake_up_all() is a crucial memory barrier after the
* list_del_init() and also before assigning to q->lock_ptr.
*/
wake_up_all(&q->waiters);
/*
* The waiting task can free the futex_q as soon as this is written,
* without taking any locks. This must come last.
*
* A memory barrier is required here to prevent the following store
* to lock_ptr from getting ahead of the wakeup. Clearing the lock
* at the end of wake_up_all() does not prevent this store from
* moving.
*/
smp_wmb();
q->lock_ptr = NULL;
}
static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)
{
struct task_struct *new_owner;
struct futex_pi_state *pi_state = this->pi_state;
u32 curval, newval;
if (!pi_state)
return -EINVAL;
new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
/*
* This happens when we have stolen the lock and the original
* pending owner did not enqueue itself back on the rt_mutex.
* Thats not a tragedy. We know that way, that a lock waiter
* is on the fly. We make the futex_q waiter the pending owner.
*/
if (!new_owner)
new_owner = this->task;
/*
* We pass it to the next owner. (The WAITERS bit is always
* kept enabled while there is PI state around. We must also
* preserve the owner died bit.)
*/
if (!(uval & FUTEX_OWNER_DIED)) {
newval = FUTEX_WAITERS | new_owner->pid;
pagefault_disable();
curval = futex_atomic_cmpxchg_inatomic(uaddr, uval, newval);
pagefault_enable();
if (curval == -EFAULT)
return -EFAULT;
if (curval != uval)
return -EINVAL;
}
spin_lock_irq(&pi_state->owner->pi_lock);
WARN_ON(list_empty(&pi_state->list));
list_del_init(&pi_state->list);
spin_unlock_irq(&pi_state->owner->pi_lock);
spin_lock_irq(&new_owner->pi_lock);
WARN_ON(!list_empty(&pi_state->list));
list_add(&pi_state->list, &new_owner->pi_state_list);
pi_state->owner = new_owner;
spin_unlock_irq(&new_owner->pi_lock);
rt_mutex_unlock(&pi_state->pi_mutex);
return 0;
}
static int unlock_futex_pi(u32 __user *uaddr, u32 uval)
{
u32 oldval;
/*
* There is no waiter, so we unlock the futex. The owner died
* bit has not to be preserved here. We are the owner:
*/
pagefault_disable();
oldval = futex_atomic_cmpxchg_inatomic(uaddr, uval, 0);
pagefault_enable();
if (oldval == -EFAULT)
return oldval;
if (oldval != uval)
return -EAGAIN;
return 0;
}
/*
* Express the locking dependencies for lockdep:
*/
static inline void
double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
{
if (hb1 <= hb2) {
spin_lock(&hb1->lock);
if (hb1 < hb2)
spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
} else { /* hb1 > hb2 */
spin_lock(&hb2->lock);
spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
}
}
/*
* Wake up all waiters hashed on the physical page that is mapped
* to this virtual address:
*/
static int futex_wake(u32 __user *uaddr, int nr_wake)
{
struct futex_hash_bucket *hb;
struct futex_q *this, *next;
struct list_head *head;
union futex_key key;
int ret;
down_read(¤t->mm->mmap_sem);
ret = get_futex_key(uaddr, &key);
if (unlikely(ret != 0))
goto out;
hb = hash_futex(&key);
spin_lock(&hb->lock);
head = &hb->chain;
list_for_each_entry_safe(this, next, head, list) {
if (match_futex (&this->key, &key)) {
if (this->pi_state) {
ret = -EINVAL;
break;
}
wake_futex(this);
if (++ret >= nr_wake)
break;
}
}
spin_unlock(&hb->lock);
out:
up_read(¤t->mm->mmap_sem);
return ret;
}
/*
* Wake up all waiters hashed on the physical page that is mapped
* to this virtual address:
*/
static int
futex_wake_op(u32 __user *uaddr1, u32 __user *uaddr2,
int nr_wake, int nr_wake2, int op)
{
union futex_key key1, key2;
struct futex_hash_bucket *hb1, *hb2;
struct list_head *head;
struct futex_q *this, *next;
int ret, op_ret, attempt = 0;
retryfull:
down_read(¤t->mm->mmap_sem);
ret = get_futex_key(uaddr1, &key1);
if (unlikely(ret != 0))
goto out;
ret = get_futex_key(uaddr2, &key2);
if (unlikely(ret != 0))
goto out;
hb1 = hash_futex(&key1);
hb2 = hash_futex(&key2);
retry:
double_lock_hb(hb1, hb2);
op_ret = futex_atomic_op_inuser(op, uaddr2);
if (unlikely(op_ret < 0)) {
u32 dummy;
spin_unlock(&hb1->lock);
if (hb1 != hb2)
spin_unlock(&hb2->lock);
#ifndef CONFIG_MMU
/*
* we don't get EFAULT from MMU faults if we don't have an MMU,
* but we might get them from range checking
*/
ret = op_ret;
goto out;
#endif
if (unlikely(op_ret != -EFAULT)) {
ret = op_ret;
goto out;
}
/*
* futex_atomic_op_inuser needs to both read and write
* *(int __user *)uaddr2, but we can't modify it
* non-atomically. Therefore, if get_user below is not
* enough, we need to handle the fault ourselves, while
* still holding the mmap_sem.
*/
if (attempt++) {
if (futex_handle_fault((unsigned long)uaddr2,
attempt)) {
ret = -EFAULT;
goto out;
}
goto retry;
}
/*
* If we would have faulted, release mmap_sem,
* fault it in and start all over again.
*/
up_read(¤t->mm->mmap_sem);
ret = get_user(dummy, uaddr2);
if (ret)
return ret;
goto retryfull;
}
head = &hb1->chain;
list_for_each_entry_safe(this, next, head, list) {
if (match_futex (&this->key, &key1)) {
wake_futex(this);
if (++ret >= nr_wake)
break;
}
}
if (op_ret > 0) {
head = &hb2->chain;
op_ret = 0;
list_for_each_entry_safe(this, next, head, list) {
if (match_futex (&this->key, &key2)) {
wake_futex(this);
if (++op_ret >= nr_wake2)
break;
}
}
ret += op_ret;
}
spin_unlock(&hb1->lock);
if (hb1 != hb2)
spin_unlock(&hb2->lock);
out:
up_read(¤t->mm->mmap_sem);
return ret;
}
/*
* Requeue all waiters hashed on one physical page to another
* physical page.
*/
static int futex_requeue(u32 __user *uaddr1, u32 __user *uaddr2,
int nr_wake, int nr_requeue, u32 *cmpval)
{
union futex_key key1, key2;
struct futex_hash_bucket *hb1, *hb2;
struct list_head *head1;
struct futex_q *this, *next;
int ret, drop_count = 0;
retry:
down_read(¤t->mm->mmap_sem);
ret = get_futex_key(uaddr1, &key1);
if (unlikely(ret != 0))
goto out;
ret = get_futex_key(uaddr2, &key2);
if (unlikely(ret != 0))
goto out;
hb1 = hash_futex(&key1);
hb2 = hash_futex(&key2);
double_lock_hb(hb1, hb2);
if (likely(cmpval != NULL)) {
u32 curval;
ret = get_futex_value_locked(&curval, uaddr1);
if (unlikely(ret)) {
spin_unlock(&hb1->lock);
if (hb1 != hb2)
spin_unlock(&hb2->lock);
/*
* If we would have faulted, release mmap_sem, fault
* it in and start all over again.
*/
up_read(¤t->mm->mmap_sem);
ret = get_user(curval, uaddr1);
if (!ret)
goto retry;
return ret;
}
if (curval != *cmpval) {
ret = -EAGAIN;
goto out_unlock;
}
}
head1 = &hb1->chain;
list_for_each_entry_safe(this, next, head1, list) {
if (!match_futex (&this->key, &key1))
continue;
if (++ret <= nr_wake) {
wake_futex(this);
} else {
/*
* If key1 and key2 hash to the same bucket, no need to
* requeue.
*/
if (likely(head1 != &hb2->chain)) {
list_move_tail(&this->list, &hb2->chain);
this->lock_ptr = &hb2->lock;
}
this->key = key2;
get_key_refs(&key2);
drop_count++;
if (ret - nr_wake >= nr_requeue)
break;
}
}
out_unlock:
spin_unlock(&hb1->lock);
if (hb1 != hb2)
spin_unlock(&hb2->lock);
/* drop_key_refs() must be called outside the spinlocks. */
while (--drop_count >= 0)
drop_key_refs(&key1);
out:
up_read(¤t->mm->mmap_sem);
return ret;
}
/* The key must be already stored in q->key. */
static inline struct futex_hash_bucket *
queue_lock(struct futex_q *q, int fd, struct file *filp)
{
struct futex_hash_bucket *hb;
q->fd = fd;
q->filp = filp;
init_waitqueue_head(&q->waiters);
get_key_refs(&q->key);
hb = hash_futex(&q->key);
q->lock_ptr = &hb->lock;
spin_lock(&hb->lock);
return hb;
}
static inline void __queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
{
list_add_tail(&q->list, &hb->chain);
q->task = current;
spin_unlock(&hb->lock);
}
static inline void
queue_unlock(struct futex_q *q, struct futex_hash_bucket *hb)
{
spin_unlock(&hb->lock);
drop_key_refs(&q->key);
}
/*
* queue_me and unqueue_me must be called as a pair, each
* exactly once. They are called with the hashed spinlock held.
*/
/* The key must be already stored in q->key. */
static void queue_me(struct futex_q *q, int fd, struct file *filp)
{
struct futex_hash_bucket *hb;
hb = queue_lock(q, fd, filp);
__queue_me(q, hb);
}
/* Return 1 if we were still queued (ie. 0 means we were woken) */
static int unqueue_me(struct futex_q *q)
{
spinlock_t *lock_ptr;
int ret = 0;
/* In the common case we don't take the spinlock, which is nice. */
retry:
lock_ptr = q->lock_ptr;
barrier();
if (lock_ptr != 0) {
spin_lock(lock_ptr);
/*
* q->lock_ptr can change between reading it and
* spin_lock(), causing us to take the wrong lock. This
* corrects the race condition.
*
* Reasoning goes like this: if we have the wrong lock,
* q->lock_ptr must have changed (maybe several times)
* between reading it and the spin_lock(). It can
* change again after the spin_lock() but only if it was
* already changed before the spin_lock(). It cannot,
* however, change back to the original value. Therefore
* we can detect whether we acquired the correct lock.
*/
if (unlikely(lock_ptr != q->lock_ptr)) {
spin_unlock(lock_ptr);
goto retry;
}
WARN_ON(list_empty(&q->list));
list_del(&q->list);
BUG_ON(q->pi_state);
spin_unlock(lock_ptr);
ret = 1;
}
drop_key_refs(&q->key);
return ret;
}
/*
* PI futexes can not be requeued and must remove themself from the
* hash bucket. The hash bucket lock is held on entry and dropped here.
*/
static void unqueue_me_pi(struct futex_q *q, struct futex_hash_bucket *hb)
{
WARN_ON(list_empty(&q->list));
list_del(&q->list);
BUG_ON(!q->pi_state);
free_pi_state(q->pi_state);
q->pi_state = NULL;
spin_unlock(&hb->lock);
drop_key_refs(&q->key);
}
static int futex_wait(u32 __user *uaddr, u32 val, unsigned long time)
{
struct task_struct *curr = current;
DECLARE_WAITQUEUE(wait, curr);
struct futex_hash_bucket *hb;
struct futex_q q;
u32 uval;
int ret;
q.pi_state = NULL;
retry:
down_read(&curr->mm->mmap_sem);
ret = get_futex_key(uaddr, &q.key);
if (unlikely(ret != 0))
goto out_release_sem;
hb = queue_lock(&q, -1, NULL);
/*
* Access the page AFTER the futex is queued.
* Order is important:
*
* Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
* Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
*
* The basic logical guarantee of a futex is that it blocks ONLY
* if cond(var) is known to be true at the time of blocking, for
* any cond. If we queued after testing *uaddr, that would open
* a race condition where we could block indefinitely with
* cond(var) false, which would violate the guarantee.
*
* A consequence is that futex_wait() can return zero and absorb
* a wakeup when *uaddr != val on entry to the syscall. This is
* rare, but normal.
*
* We hold the mmap semaphore, so the mapping cannot have changed
* since we looked it up in get_futex_key.
*/
ret = get_futex_value_locked(&uval, uaddr);
if (unlikely(ret)) {
queue_unlock(&q, hb);
/*
* If we would have faulted, release mmap_sem, fault it in and
* start all over again.
*/
up_read(&curr->mm->mmap_sem);
ret = get_user(uval, uaddr);
if (!ret)
goto retry;
return ret;
}
ret = -EWOULDBLOCK;
if (uval != val)
goto out_unlock_release_sem;
/* Only actually queue if *uaddr contained val. */
__queue_me(&q, hb);
/*
* Now the futex is queued and we have checked the data, we
* don't want to hold mmap_sem while we sleep.
*/
up_read(&curr->mm->mmap_sem);
/*
* There might have been scheduling since the queue_me(), as we
* cannot hold a spinlock across the get_user() in case it
* faults, and we cannot just set TASK_INTERRUPTIBLE state when
* queueing ourselves into the futex hash. This code thus has to
* rely on the futex_wake() code removing us from hash when it
* wakes us up.
*/
/* add_wait_queue is the barrier after __set_current_state. */
__set_current_state(TASK_INTERRUPTIBLE);
add_wait_queue(&q.waiters, &wait);
/*
* !list_empty() is safe here without any lock.
* q.lock_ptr != 0 is not safe, because of ordering against wakeup.
*/
if (likely(!list_empty(&q.list)))
time = schedule_timeout(time);
__set_current_state(TASK_RUNNING);
/*
* NOTE: we don't remove ourselves from the waitqueue because
* we are the only user of it.
*/
/* If we were woken (and unqueued), we succeeded, whatever. */
if (!unqueue_me(&q))
return 0;
if (time == 0)
return -ETIMEDOUT;
/*
* We expect signal_pending(current), but another thread may
* have handled it for us already.
*/
return -EINTR;
out_unlock_release_sem:
queue_unlock(&q, hb);
out_release_sem:
up_read(&curr->mm->mmap_sem);
return ret;
}
/*
* Userspace tried a 0 -> TID atomic transition of the futex value
* and failed. The kernel side here does the whole locking operation:
* if there are waiters then it will block, it does PI, etc. (Due to
* races the kernel might see a 0 value of the futex too.)
*/
static int futex_lock_pi(u32 __user *uaddr, int detect, unsigned long sec,
long nsec, int trylock)
{
struct hrtimer_sleeper timeout, *to = NULL;
struct task_struct *curr = current;
struct futex_hash_bucket *hb;
u32 uval, newval, curval;
struct futex_q q;
int ret, attempt = 0;
if (refill_pi_state_cache())
return -ENOMEM;
if (sec != MAX_SCHEDULE_TIMEOUT) {
to = &timeout;
hrtimer_init(&to->timer, CLOCK_REALTIME, HRTIMER_ABS);
hrtimer_init_sleeper(to, current);
to->timer.expires = ktime_set(sec, nsec);
}
q.pi_state = NULL;
retry:
down_read(&curr->mm->mmap_sem);
ret = get_futex_key(uaddr, &q.key);
if (unlikely(ret != 0))
goto out_release_sem;
hb = queue_lock(&q, -1, NULL);
retry_locked:
/*
* To avoid races, we attempt to take the lock here again
* (by doing a 0 -> TID atomic cmpxchg), while holding all
* the locks. It will most likely not succeed.
*/
newval = current->pid;
pagefault_disable();
curval = futex_atomic_cmpxchg_inatomic(uaddr, 0, newval);
pagefault_enable();
if (unlikely(curval == -EFAULT))
goto uaddr_faulted;
/* We own the lock already */
if (unlikely((curval & FUTEX_TID_MASK) == current->pid)) {
if (!detect && 0)
force_sig(SIGKILL, current);
ret = -EDEADLK;
goto out_unlock_release_sem;
}
/*
* Surprise - we got the lock. Just return
* to userspace:
*/
if (unlikely(!curval))
goto out_unlock_release_sem;
uval = curval;
newval = uval | FUTEX_WAITERS;
pagefault_disable();
curval = futex_atomic_cmpxchg_inatomic(uaddr, uval, newval);
pagefault_enable();
if (unlikely(curval == -EFAULT))
goto uaddr_faulted;
if (unlikely(curval != uval))
goto retry_locked;
/*
* We dont have the lock. Look up the PI state (or create it if
* we are the first waiter):
*/
ret = lookup_pi_state(uval, hb, &q);
if (unlikely(ret)) {
/*
* There were no waiters and the owner task lookup
* failed. When the OWNER_DIED bit is set, then we
* know that this is a robust futex and we actually
* take the lock. This is safe as we are protected by
* the hash bucket lock. We also set the waiters bit
* unconditionally here, to simplify glibc handling of
* multiple tasks racing to acquire the lock and
* cleanup the problems which were left by the dead
* owner.
*/
if (curval & FUTEX_OWNER_DIED) {
uval = newval;
newval = current->pid |
FUTEX_OWNER_DIED | FUTEX_WAITERS;
pagefault_disable();
curval = futex_atomic_cmpxchg_inatomic(uaddr,
uval, newval);
pagefault_enable();
if (unlikely(curval == -EFAULT))
goto uaddr_faulted;
if (unlikely(curval != uval))
goto retry_locked;
ret = 0;
}
goto out_unlock_release_sem;
}
/*
* Only actually queue now that the atomic ops are done:
*/
__queue_me(&q, hb);
/*
* Now the futex is queued and we have checked the data, we
* don't want to hold mmap_sem while we sleep.
*/
up_read(&curr->mm->mmap_sem);
WARN_ON(!q.pi_state);
/*
* Block on the PI mutex:
*/
if (!trylock)
ret = rt_mutex_timed_lock(&q.pi_state->pi_mutex, to, 1);
else {
ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
/* Fixup the trylock return value: */
ret = ret ? 0 : -EWOULDBLOCK;
}
down_read(&curr->mm->mmap_sem);
spin_lock(q.lock_ptr);
/*
* Got the lock. We might not be the anticipated owner if we
* did a lock-steal - fix up the PI-state in that case.
*/
if (!ret && q.pi_state->owner != curr) {
u32 newtid = current->pid | FUTEX_WAITERS;
/* Owner died? */
if (q.pi_state->owner != NULL) {
spin_lock_irq(&q.pi_state->owner->pi_lock);
WARN_ON(list_empty(&q.pi_state->list));
list_del_init(&q.pi_state->list);
spin_unlock_irq(&q.pi_state->owner->pi_lock);
} else
newtid |= FUTEX_OWNER_DIED;
q.pi_state->owner = current;
spin_lock_irq(¤t->pi_lock);
WARN_ON(!list_empty(&q.pi_state->list));
list_add(&q.pi_state->list, ¤t->pi_state_list);
spin_unlock_irq(¤t->pi_lock);
/* Unqueue and drop the lock */
unqueue_me_pi(&q, hb);
up_read(&curr->mm->mmap_sem);
/*
* We own it, so we have to replace the pending owner
* TID. This must be atomic as we have preserve the
* owner died bit here.
*/
ret = get_user(uval, uaddr);
while (!ret) {
newval = (uval & FUTEX_OWNER_DIED) | newtid;
curval = futex_atomic_cmpxchg_inatomic(uaddr,
uval, newval);
if (curval == -EFAULT)
ret = -EFAULT;
if (curval == uval)
break;
uval = curval;
}
} else {
/*
* Catch the rare case, where the lock was released
* when we were on the way back before we locked
* the hash bucket.
*/
if (ret && q.pi_state->owner == curr) {
if (rt_mutex_trylock(&q.pi_state->pi_mutex))
ret = 0;
}
/* Unqueue and drop the lock */
unqueue_me_pi(&q, hb);
up_read(&curr->mm->mmap_sem);
}
if (!detect && ret == -EDEADLK && 0)
force_sig(SIGKILL, current);
return ret != -EINTR ? ret : -ERESTARTNOINTR;
out_unlock_release_sem:
queue_unlock(&q, hb);
out_release_sem:
up_read(&curr->mm->mmap_sem);
return ret;
uaddr_faulted:
/*
* We have to r/w *(int __user *)uaddr, but we can't modify it
* non-atomically. Therefore, if get_user below is not
* enough, we need to handle the fault ourselves, while
* still holding the mmap_sem.
*/
if (attempt++) {
if (futex_handle_fault((unsigned long)uaddr, attempt)) {
ret = -EFAULT;
goto out_unlock_release_sem;
}
goto retry_locked;
}
queue_unlock(&q, hb);
up_read(&curr->mm->mmap_sem);
ret = get_user(uval, uaddr);
if (!ret && (uval != -EFAULT))
goto retry;
return ret;
}
/*
* Userspace attempted a TID -> 0 atomic transition, and failed.
* This is the in-kernel slowpath: we look up the PI state (if any),
* and do the rt-mutex unlock.
*/
static int futex_unlock_pi(u32 __user *uaddr)
{
struct futex_hash_bucket *hb;
struct futex_q *this, *next;
u32 uval;
struct list_head *head;
union futex_key key;
int ret, attempt = 0;
retry:
if (get_user(uval, uaddr))
return -EFAULT;
/*
* We release only a lock we actually own:
*/
if ((uval & FUTEX_TID_MASK) != current->pid)
return -EPERM;
/*
* First take all the futex related locks:
*/
down_read(¤t->mm->mmap_sem);
ret = get_futex_key(uaddr, &key);
if (unlikely(ret != 0))
goto out;
hb = hash_futex(&key);
spin_lock(&hb->lock);
retry_locked:
/*
* To avoid races, try to do the TID -> 0 atomic transition
* again. If it succeeds then we can return without waking
* anyone else up:
*/
if (!(uval & FUTEX_OWNER_DIED)) {
pagefault_disable();
uval = futex_atomic_cmpxchg_inatomic(uaddr, current->pid, 0);
pagefault_enable();
}
if (unlikely(uval == -EFAULT))
goto pi_faulted;
/*
* Rare case: we managed to release the lock atomically,
* no need to wake anyone else up:
*/
if (unlikely(uval == current->pid))
goto out_unlock;
/*
* Ok, other tasks may need to be woken up - check waiters
* and do the wakeup if necessary:
*/
head = &hb->chain;
list_for_each_entry_safe(this, next, head, list) {
if (!match_futex (&this->key, &key))
continue;
ret = wake_futex_pi(uaddr, uval, this);
/*
* The atomic access to the futex value
* generated a pagefault, so retry the
* user-access and the wakeup:
*/
if (ret == -EFAULT)
goto pi_faulted;
goto out_unlock;
}
/*
* No waiters - kernel unlocks the futex:
*/
if (!(uval & FUTEX_OWNER_DIED)) {
ret = unlock_futex_pi(uaddr, uval);
if (ret == -EFAULT)
goto pi_faulted;
}
out_unlock:
spin_unlock(&hb->lock);
out:
up_read(¤t->mm->mmap_sem);
return ret;
pi_faulted:
/*
* We have to r/w *(int __user *)uaddr, but we can't modify it
* non-atomically. Therefore, if get_user below is not
* enough, we need to handle the fault ourselves, while
* still holding the mmap_sem.
*/
if (attempt++) {
if (futex_handle_fault((unsigned long)uaddr, attempt)) {
ret = -EFAULT;
goto out_unlock;
}
goto retry_locked;
}
spin_unlock(&hb->lock);
up_read(¤t->mm->mmap_sem);
ret = get_user(uval, uaddr);
if (!ret && (uval != -EFAULT))
goto retry;
return ret;
}
static int futex_close(struct inode *inode, struct file *filp)
{
struct futex_q *q = filp->private_data;
unqueue_me(q);
kfree(q);
return 0;
}
/* This is one-shot: once it's gone off you need a new fd */
static unsigned int futex_poll(struct file *filp,
struct poll_table_struct *wait)
{
struct futex_q *q = filp->private_data;
int ret = 0;
poll_wait(filp, &q->waiters, wait);
/*
* list_empty() is safe here without any lock.
* q->lock_ptr != 0 is not safe, because of ordering against wakeup.
*/
if (list_empty(&q->list))
ret = POLLIN | POLLRDNORM;
return ret;
}
static const struct file_operations futex_fops = {
.release = futex_close,
.poll = futex_poll,
};
/*
* Signal allows caller to avoid the race which would occur if they
* set the sigio stuff up afterwards.
*/
static int futex_fd(u32 __user *uaddr, int signal)
{
struct futex_q *q;
struct file *filp;
int ret, err;
static unsigned long printk_interval;
if (printk_timed_ratelimit(&printk_interval, 60 * 60 * 1000)) {
printk(KERN_WARNING "Process `%s' used FUTEX_FD, which "
"will be removed from the kernel in June 2007\n",
current->comm);
}
ret = -EINVAL;
if (!valid_signal(signal))
goto out;
ret = get_unused_fd();
if (ret < 0)
goto out;
filp = get_empty_filp();
if (!filp) {
put_unused_fd(ret);
ret = -ENFILE;
goto out;
}
filp->f_op = &futex_fops;
filp->f_path.mnt = mntget(futex_mnt);
filp->f_path.dentry = dget(futex_mnt->mnt_root);
filp->f_mapping = filp->f_path.dentry->d_inode->i_mapping;
if (signal) {
err = __f_setown(filp, task_pid(current), PIDTYPE_PID, 1);
if (err < 0) {
goto error;
}
filp->f_owner.signum = signal;
}
q = kmalloc(sizeof(*q), GFP_KERNEL);
if (!q) {
err = -ENOMEM;
goto error;
}
q->pi_state = NULL;
down_read(¤t->mm->mmap_sem);
err = get_futex_key(uaddr, &q->key);
if (unlikely(err != 0)) {
up_read(¤t->mm->mmap_sem);
kfree(q);
goto error;
}
/*
* queue_me() must be called before releasing mmap_sem, because
* key->shared.inode needs to be referenced while holding it.
*/
filp->private_data = q;
queue_me(q, ret, filp);
up_read(¤t->mm->mmap_sem);
/* Now we map fd to filp, so userspace can access it */
fd_install(ret, filp);
out:
return ret;
error:
put_unused_fd(ret);
put_filp(filp);
ret = err;
goto out;
}
/*
* Support for robust futexes: the kernel cleans up held futexes at
* thread exit time.
*
* Implementation: user-space maintains a per-thread list of locks it
* is holding. Upon do_exit(), the kernel carefully walks this list,
* and marks all locks that are owned by this thread with the
* FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
* always manipulated with the lock held, so the list is private and
* per-thread. Userspace also maintains a per-thread 'list_op_pending'
* field, to allow the kernel to clean up if the thread dies after
* acquiring the lock, but just before it could have added itself to
* the list. There can only be one such pending lock.
*/
/**
* sys_set_robust_list - set the robust-futex list head of a task
* @head: pointer to the list-head
* @len: length of the list-head, as userspace expects
*/
asmlinkage long
sys_set_robust_list(struct robust_list_head __user *head,
size_t len)
{
/*
* The kernel knows only one size for now:
*/
if (unlikely(len != sizeof(*head)))
return -EINVAL;
current->robust_list = head;
return 0;
}
/**
* sys_get_robust_list - get the robust-futex list head of a task
* @pid: pid of the process [zero for current task]
* @head_ptr: pointer to a list-head pointer, the kernel fills it in
* @len_ptr: pointer to a length field, the kernel fills in the header size
*/
asmlinkage long
sys_get_robust_list(int pid, struct robust_list_head __user * __user *head_ptr,
size_t __user *len_ptr)
{
struct robust_list_head __user *head;
unsigned long ret;
if (!pid)
head = current->robust_list;
else {
struct task_struct *p;
ret = -ESRCH;
rcu_read_lock();
p = find_task_by_pid(pid);
if (!p)
goto err_unlock;
ret = -EPERM;
if ((current->euid != p->euid) && (current->euid != p->uid) &&
!capable(CAP_SYS_PTRACE))
goto err_unlock;
head = p->robust_list;
rcu_read_unlock();
}
if (put_user(sizeof(*head), len_ptr))
return -EFAULT;
return put_user(head, head_ptr);
err_unlock:
rcu_read_unlock();
return ret;
}
/*
* Process a futex-list entry, check whether it's owned by the
* dying task, and do notification if so:
*/
int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
{
u32 uval, nval, mval;
retry:
if (get_user(uval, uaddr))
return -1;
if ((uval & FUTEX_TID_MASK) == curr->pid) {
/*
* Ok, this dying thread is truly holding a futex
* of interest. Set the OWNER_DIED bit atomically
* via cmpxchg, and if the value had FUTEX_WAITERS
* set, wake up a waiter (if any). (We have to do a
* futex_wake() even if OWNER_DIED is already set -
* to handle the rare but possible case of recursive
* thread-death.) The rest of the cleanup is done in
* userspace.
*/
mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
nval = futex_atomic_cmpxchg_inatomic(uaddr, uval, mval);
if (nval == -EFAULT)
return -1;
if (nval != uval)
goto retry;
/*
* Wake robust non-PI futexes here. The wakeup of
* PI futexes happens in exit_pi_state():
*/
if (!pi) {
if (uval & FUTEX_WAITERS)
futex_wake(uaddr, 1);
}
}
return 0;
}
/*
* Fetch a robust-list pointer. Bit 0 signals PI futexes:
*/
static inline int fetch_robust_entry(struct robust_list __user **entry,
struct robust_list __user * __user *head,
int *pi)
{
unsigned long uentry;
if (get_user(uentry, (unsigned long __user *)head))
return -EFAULT;
*entry = (void __user *)(uentry & ~1UL);
*pi = uentry & 1;
return 0;
}
/*
* Walk curr->robust_list (very carefully, it's a userspace list!)
* and mark any locks found there dead, and notify any waiters.
*
* We silently return on any sign of list-walking problem.
*/
void exit_robust_list(struct task_struct *curr)
{
struct robust_list_head __user *head = curr->robust_list;
struct robust_list __user *entry, *pending;
unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
unsigned long futex_offset;
/*
* Fetch the list head (which was registered earlier, via
* sys_set_robust_list()):
*/
if (fetch_robust_entry(&entry, &head->list.next, &pi))
return;
/*
* Fetch the relative futex offset:
*/
if (get_user(futex_offset, &head->futex_offset))
return;
/*
* Fetch any possibly pending lock-add first, and handle it
* if it exists:
*/
if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
return;
if (pending)
handle_futex_death((void __user *)pending + futex_offset, curr, pip);
while (entry != &head->list) {
/*
* A pending lock might already be on the list, so
* don't process it twice:
*/
if (entry != pending)
if (handle_futex_death((void __user *)entry + futex_offset,
curr, pi))
return;
/*
* Fetch the next entry in the list:
*/
if (fetch_robust_entry(&entry, &entry->next, &pi))
return;
/*
* Avoid excessively long or circular lists:
*/
if (!--limit)
break;
cond_resched();
}
}
long do_futex(u32 __user *uaddr, int op, u32 val, unsigned long timeout,
u32 __user *uaddr2, u32 val2, u32 val3)
{
int ret;
switch (op) {
case FUTEX_WAIT:
ret = futex_wait(uaddr, val, timeout);
break;
case FUTEX_WAKE:
ret = futex_wake(uaddr, val);
break;
case FUTEX_FD:
/* non-zero val means F_SETOWN(getpid()) & F_SETSIG(val) */
ret = futex_fd(uaddr, val);
break;
case FUTEX_REQUEUE:
ret = futex_requeue(uaddr, uaddr2, val, val2, NULL);
break;
case FUTEX_CMP_REQUEUE:
ret = futex_requeue(uaddr, uaddr2, val, val2, &val3);
break;
case FUTEX_WAKE_OP:
ret = futex_wake_op(uaddr, uaddr2, val, val2, val3);
break;
case FUTEX_LOCK_PI:
ret = futex_lock_pi(uaddr, val, timeout, val2, 0);
break;
case FUTEX_UNLOCK_PI:
ret = futex_unlock_pi(uaddr);
break;
case FUTEX_TRYLOCK_PI:
ret = futex_lock_pi(uaddr, 0, timeout, val2, 1);
break;
default:
ret = -ENOSYS;
}
return ret;
}
asmlinkage long sys_futex(u32 __user *uaddr, int op, u32 val,
struct timespec __user *utime, u32 __user *uaddr2,
u32 val3)
{
struct timespec t;
unsigned long timeout = MAX_SCHEDULE_TIMEOUT;
u32 val2 = 0;
if (utime && (op == FUTEX_WAIT || op == FUTEX_LOCK_PI)) {
if (copy_from_user(&t, utime, sizeof(t)) != 0)
return -EFAULT;
if (!timespec_valid(&t))
return -EINVAL;
if (op == FUTEX_WAIT)
timeout = timespec_to_jiffies(&t) + 1;
else {
timeout = t.tv_sec;
val2 = t.tv_nsec;
}
}
/*
* requeue parameter in 'utime' if op == FUTEX_REQUEUE.
*/
if (op == FUTEX_REQUEUE || op == FUTEX_CMP_REQUEUE)
val2 = (u32) (unsigned long) utime;
return do_futex(uaddr, op, val, timeout, uaddr2, val2, val3);
}
static int futexfs_get_sb(struct file_system_type *fs_type,
int flags, const char *dev_name, void *data,
struct vfsmount *mnt)
{
return get_sb_pseudo(fs_type, "futex", NULL, 0xBAD1DEA, mnt);
}
static struct file_system_type futex_fs_type = {
.name = "futexfs",
.get_sb = futexfs_get_sb,
.kill_sb = kill_anon_super,
};
static int __init init(void)
{
int i = register_filesystem(&futex_fs_type);
if (i)
return i;
futex_mnt = kern_mount(&futex_fs_type);
if (IS_ERR(futex_mnt)) {
unregister_filesystem(&futex_fs_type);
return PTR_ERR(futex_mnt);
}
for (i = 0; i < ARRAY_SIZE(futex_queues); i++) {
INIT_LIST_HEAD(&futex_queues[i].chain);
spin_lock_init(&futex_queues[i].lock);
}
return 0;
}
__initcall(init);
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