android_kernel_xiaomi_sm8350/kernel/futex.c
Thomas Gleixner cdf71a10c7 futex: Prevent stale futex owner when interrupted/timeout
Roland Westrelin did a great analysis of a long standing thinko in the
return path of futex_lock_pi.

While we fixed the lock steal case long ago, which was easy to trigger,
we never had a test case which exposed this problem and stupidly never
thought about the reverse lock stealing scenario and the return to user
space with a stale state.

When a blocked tasks returns from rt_mutex_timed_locked without holding
the rt_mutex (due to a signal or timeout) and at the same time the task
holding the futex is releasing the futex and assigning the ownership of
the futex to the returning task, then it might happen that a third task
acquires the rt_mutex before the final rt_mutex_trylock() of the
returning task happens under the futex hash bucket lock. The returning
task returns to user space with ETIMEOUT or EINTR, but the user space
futex value is assigned to this task. The task which acquired the
rt_mutex fixes the user space futex value right after the hash bucket
lock has been released by the returning task, but for a short period of
time the user space value is wrong.

Detailed description is available at:

   https://bugzilla.redhat.com/show_bug.cgi?id=400541

The fix for this is the same as we do when the rt_mutex was acquired by
a higher priority task via lock stealing from the designated new owner.
In that case we already fix the user space value and the internal
pi_state up before we return. This mechanism can be used to fixup the
above corner case as well. When the returning task, which failed to
acquire the rt_mutex, notices that it is the designated owner of the
futex, then it fixes up the stale user space value and the pi_state,
before returning to user space. This happens with the futex hash bucket
lock held, so the task which acquired the rt_mutex is guaranteed to be
blocked on the hash bucket lock. We can access the rt_mutex owner, which
gives us the pid of the new owner, safely here as the owner is not able
to modify (release) it while waiting on the hash bucket lock.

Rename the "curr" argument of fixup_pi_state_owner() to "newowner" to
avoid confusion with current and add the check for the stale state into
the failure path of rt_mutex_trylock() in the return path of
unlock_futex_pi(). If the situation is detected use
fixup_pi_state_owner() to assign everything to the owner of the
rt_mutex.

Pointed-out-and-tested-by: Roland Westrelin <roland.westrelin@sun.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-01-08 16:21:39 -08:00

2144 lines
51 KiB
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>
*
* PRIVATE futexes by Eric Dumazet
* Copyright (C) 2007 Eric Dumazet <dada1@cosmosbay.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 <linux/module.h>
#include <linux/magic.h>
#include <linux/pid.h>
#include <linux/nsproxy.h>
#include <asm/futex.h>
#include "rtmutex_common.h"
#define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8)
/*
* 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 plist_node_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 plist_node 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 plist_head chain;
};
static struct futex_hash_bucket futex_queues[1<<FUTEX_HASHBITS];
/* Futex-fs vfsmount entry: */
static struct vfsmount *futex_mnt;
/*
* Take mm->mmap_sem, when futex is shared
*/
static inline void futex_lock_mm(struct rw_semaphore *fshared)
{
if (fshared)
down_read(fshared);
}
/*
* Release mm->mmap_sem, when the futex is shared
*/
static inline void futex_unlock_mm(struct rw_semaphore *fshared)
{
if (fshared)
up_read(fshared);
}
/*
* 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_futex_key - Get parameters which are the keys for a futex.
* @uaddr: virtual address of the futex
* @shared: NULL for a PROCESS_PRIVATE futex,
* &current->mm->mmap_sem for a PROCESS_SHARED futex
* @key: address where result is stored.
*
* Returns a negative error code or 0
* The key words are stored in *key on success.
*
* 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.
*
* fshared is NULL for PROCESS_PRIVATE futexes
* For other futexes, it points to &current->mm->mmap_sem and
* caller must have taken the reader lock. but NOT any spinlocks.
*/
static int get_futex_key(u32 __user *uaddr, struct rw_semaphore *fshared,
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((address % sizeof(u32)) != 0))
return -EINVAL;
address -= key->both.offset;
/*
* PROCESS_PRIVATE futexes are fast.
* As the mm cannot disappear under us and the 'key' only needs
* virtual address, we dont even have to find the underlying vma.
* Note : We do have to check 'uaddr' is a valid user address,
* but access_ok() should be faster than find_vma()
*/
if (!fshared) {
if (unlikely(!access_ok(VERIFY_WRITE, uaddr, sizeof(u32))))
return -EFAULT;
key->private.mm = mm;
key->private.address = address;
return 0;
}
/*
* 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->both.offset |= FUT_OFF_MMSHARED; /* reference taken on mm */
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 |= FUT_OFF_INODE; /* 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.
*
*/
static void get_futex_key_refs(union futex_key *key)
{
if (key->both.ptr == 0)
return;
switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
case FUT_OFF_INODE:
atomic_inc(&key->shared.inode->i_count);
break;
case FUT_OFF_MMSHARED:
atomic_inc(&key->private.mm->mm_count);
break;
}
}
/*
* Drop a reference to the resource addressed by a key.
* The hash bucket spinlock must not be held.
*/
static void drop_futex_key_refs(union futex_key *key)
{
if (!key->both.ptr)
return;
switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
case FUT_OFF_INODE:
iput(key->shared.inode);
break;
case FUT_OFF_MMSHARED:
mmdrop(key->private.mm);
break;
}
}
static u32 cmpxchg_futex_value_locked(u32 __user *uaddr, u32 uval, u32 newval)
{
u32 curval;
pagefault_disable();
curval = futex_atomic_cmpxchg_inatomic(uaddr, uval, newval);
pagefault_enable();
return curval;
}
static 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.
* if fshared is non NULL, current->mm->mmap_sem is already held
*/
static int futex_handle_fault(unsigned long address,
struct rw_semaphore *fshared, int attempt)
{
struct vm_area_struct * vma;
struct mm_struct *mm = current->mm;
int ret = -EFAULT;
if (attempt > 2)
return ret;
if (!fshared)
down_read(&mm->mmap_sem);
vma = find_vma(mm, address);
if (vma && address >= vma->vm_start &&
(vma->vm_flags & VM_WRITE)) {
int fault;
fault = handle_mm_fault(mm, vma, address, 1);
if (unlikely((fault & VM_FAULT_ERROR))) {
#if 0
/* XXX: let's do this when we verify it is OK */
if (ret & VM_FAULT_OOM)
ret = -ENOMEM;
#endif
} else {
ret = 0;
if (fault & VM_FAULT_MAJOR)
current->maj_flt++;
else
current->min_flt++;
}
}
if (!fshared)
up_read(&mm->mmap_sem);
return ret;
}
/*
* 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_vpid(pid);
if (!p || ((current->euid != p->euid) && (current->euid != p->uid)))
p = ERR_PTR(-ESRCH);
else
get_task_struct(p);
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,
union futex_key *key, struct futex_pi_state **ps)
{
struct futex_pi_state *pi_state = NULL;
struct futex_q *this, *next;
struct plist_head *head;
struct task_struct *p;
pid_t pid = uval & FUTEX_TID_MASK;
head = &hb->chain;
plist_for_each_entry_safe(this, next, head, list) {
if (match_futex(&this->key, 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));
WARN_ON(pid && pi_state->owner &&
pi_state->owner->pid != pid);
atomic_inc(&pi_state->refcount);
*ps = 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 TID = 0
*/
if (!pid)
return -ESRCH;
p = futex_find_get_task(pid);
if (IS_ERR(p))
return PTR_ERR(p);
/*
* We need to look at the task state flags to figure out,
* whether the task is exiting. To protect against the do_exit
* change of the task flags, we do this protected by
* p->pi_lock:
*/
spin_lock_irq(&p->pi_lock);
if (unlikely(p->flags & PF_EXITING)) {
/*
* The task is on the way out. When PF_EXITPIDONE is
* set, we know that the task has finished the
* cleanup:
*/
int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN;
spin_unlock_irq(&p->pi_lock);
put_task_struct(p);
return ret;
}
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 = *key;
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);
*ps = 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)
{
plist_del(&q->list, &q->list.plist);
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
* plist_del() 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;
spin_lock(&pi_state->pi_mutex.wait_lock);
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)) {
int ret = 0;
newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
if (curval == -EFAULT)
ret = -EFAULT;
else if (curval != uval)
ret = -EINVAL;
if (ret) {
spin_unlock(&pi_state->pi_mutex.wait_lock);
return ret;
}
}
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);
spin_unlock(&pi_state->pi_mutex.wait_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:
*/
oldval = cmpxchg_futex_value_locked(uaddr, uval, 0);
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, struct rw_semaphore *fshared,
int nr_wake)
{
struct futex_hash_bucket *hb;
struct futex_q *this, *next;
struct plist_head *head;
union futex_key key;
int ret;
futex_lock_mm(fshared);
ret = get_futex_key(uaddr, fshared, &key);
if (unlikely(ret != 0))
goto out;
hb = hash_futex(&key);
spin_lock(&hb->lock);
head = &hb->chain;
plist_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:
futex_unlock_mm(fshared);
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, struct rw_semaphore *fshared,
u32 __user *uaddr2,
int nr_wake, int nr_wake2, int op)
{
union futex_key key1, key2;
struct futex_hash_bucket *hb1, *hb2;
struct plist_head *head;
struct futex_q *this, *next;
int ret, op_ret, attempt = 0;
retryfull:
futex_lock_mm(fshared);
ret = get_futex_key(uaddr1, fshared, &key1);
if (unlikely(ret != 0))
goto out;
ret = get_futex_key(uaddr2, fshared, &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++) {
ret = futex_handle_fault((unsigned long)uaddr2,
fshared, attempt);
if (ret)
goto out;
goto retry;
}
/*
* If we would have faulted, release mmap_sem,
* fault it in and start all over again.
*/
futex_unlock_mm(fshared);
ret = get_user(dummy, uaddr2);
if (ret)
return ret;
goto retryfull;
}
head = &hb1->chain;
plist_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;
plist_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:
futex_unlock_mm(fshared);
return ret;
}
/*
* Requeue all waiters hashed on one physical page to another
* physical page.
*/
static int futex_requeue(u32 __user *uaddr1, struct rw_semaphore *fshared,
u32 __user *uaddr2,
int nr_wake, int nr_requeue, u32 *cmpval)
{
union futex_key key1, key2;
struct futex_hash_bucket *hb1, *hb2;
struct plist_head *head1;
struct futex_q *this, *next;
int ret, drop_count = 0;
retry:
futex_lock_mm(fshared);
ret = get_futex_key(uaddr1, fshared, &key1);
if (unlikely(ret != 0))
goto out;
ret = get_futex_key(uaddr2, fshared, &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.
*/
futex_unlock_mm(fshared);
ret = get_user(curval, uaddr1);
if (!ret)
goto retry;
return ret;
}
if (curval != *cmpval) {
ret = -EAGAIN;
goto out_unlock;
}
}
head1 = &hb1->chain;
plist_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)) {
plist_del(&this->list, &hb1->chain);
plist_add(&this->list, &hb2->chain);
this->lock_ptr = &hb2->lock;
#ifdef CONFIG_DEBUG_PI_LIST
this->list.plist.lock = &hb2->lock;
#endif
}
this->key = key2;
get_futex_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_futex_key_refs() must be called outside the spinlocks. */
while (--drop_count >= 0)
drop_futex_key_refs(&key1);
out:
futex_unlock_mm(fshared);
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_futex_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)
{
int prio;
/*
* The priority used to register this element is
* - either the real thread-priority for the real-time threads
* (i.e. threads with a priority lower than MAX_RT_PRIO)
* - or MAX_RT_PRIO for non-RT threads.
* Thus, all RT-threads are woken first in priority order, and
* the others are woken last, in FIFO order.
*/
prio = min(current->normal_prio, MAX_RT_PRIO);
plist_node_init(&q->list, prio);
#ifdef CONFIG_DEBUG_PI_LIST
q->list.plist.lock = &hb->lock;
#endif
plist_add(&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_futex_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 != NULL) {
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(plist_node_empty(&q->list));
plist_del(&q->list, &q->list.plist);
BUG_ON(q->pi_state);
spin_unlock(lock_ptr);
ret = 1;
}
drop_futex_key_refs(&q->key);
return ret;
}
/*
* PI futexes can not be requeued and must remove themself from the
* hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
* and dropped here.
*/
static void unqueue_me_pi(struct futex_q *q)
{
WARN_ON(plist_node_empty(&q->list));
plist_del(&q->list, &q->list.plist);
BUG_ON(!q->pi_state);
free_pi_state(q->pi_state);
q->pi_state = NULL;
spin_unlock(q->lock_ptr);
drop_futex_key_refs(&q->key);
}
/*
* Fixup the pi_state owner with the new owner.
*
* Must be called with hash bucket lock held and mm->sem held for non
* private futexes.
*/
static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
struct task_struct *newowner)
{
u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
struct futex_pi_state *pi_state = q->pi_state;
u32 uval, curval, newval;
int ret;
/* Owner died? */
if (pi_state->owner != NULL) {
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);
} else
newtid |= FUTEX_OWNER_DIED;
pi_state->owner = newowner;
spin_lock_irq(&newowner->pi_lock);
WARN_ON(!list_empty(&pi_state->list));
list_add(&pi_state->list, &newowner->pi_state_list);
spin_unlock_irq(&newowner->pi_lock);
/*
* 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_futex_value_locked(&uval, uaddr);
while (!ret) {
newval = (uval & FUTEX_OWNER_DIED) | newtid;
curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
if (curval == -EFAULT)
ret = -EFAULT;
if (curval == uval)
break;
uval = curval;
}
return ret;
}
/*
* In case we must use restart_block to restart a futex_wait,
* we encode in the 'flags' shared capability
*/
#define FLAGS_SHARED 1
static long futex_wait_restart(struct restart_block *restart);
static int futex_wait(u32 __user *uaddr, struct rw_semaphore *fshared,
u32 val, ktime_t *abs_time)
{
struct task_struct *curr = current;
DECLARE_WAITQUEUE(wait, curr);
struct futex_hash_bucket *hb;
struct futex_q q;
u32 uval;
int ret;
struct hrtimer_sleeper t;
int rem = 0;
q.pi_state = NULL;
retry:
futex_lock_mm(fshared);
ret = get_futex_key(uaddr, fshared, &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.
*
* for shared futexes, 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.
*/
futex_unlock_mm(fshared);
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.
*/
futex_unlock_mm(fshared);
/*
* 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);
/*
* !plist_node_empty() is safe here without any lock.
* q.lock_ptr != 0 is not safe, because of ordering against wakeup.
*/
if (likely(!plist_node_empty(&q.list))) {
if (!abs_time)
schedule();
else {
hrtimer_init(&t.timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
hrtimer_init_sleeper(&t, current);
t.timer.expires = *abs_time;
hrtimer_start(&t.timer, t.timer.expires, HRTIMER_MODE_ABS);
/*
* the timer could have already expired, in which
* case current would be flagged for rescheduling.
* Don't bother calling schedule.
*/
if (likely(t.task))
schedule();
hrtimer_cancel(&t.timer);
/* Flag if a timeout occured */
rem = (t.task == NULL);
}
}
__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 (rem)
return -ETIMEDOUT;
/*
* We expect signal_pending(current), but another thread may
* have handled it for us already.
*/
if (!abs_time)
return -ERESTARTSYS;
else {
struct restart_block *restart;
restart = &current_thread_info()->restart_block;
restart->fn = futex_wait_restart;
restart->futex.uaddr = (u32 *)uaddr;
restart->futex.val = val;
restart->futex.time = abs_time->tv64;
restart->futex.flags = 0;
if (fshared)
restart->futex.flags |= FLAGS_SHARED;
return -ERESTART_RESTARTBLOCK;
}
out_unlock_release_sem:
queue_unlock(&q, hb);
out_release_sem:
futex_unlock_mm(fshared);
return ret;
}
static long futex_wait_restart(struct restart_block *restart)
{
u32 __user *uaddr = (u32 __user *)restart->futex.uaddr;
struct rw_semaphore *fshared = NULL;
ktime_t t;
t.tv64 = restart->futex.time;
restart->fn = do_no_restart_syscall;
if (restart->futex.flags & FLAGS_SHARED)
fshared = &current->mm->mmap_sem;
return (long)futex_wait(uaddr, fshared, restart->futex.val, &t);
}
/*
* 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, struct rw_semaphore *fshared,
int detect, ktime_t *time, 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, lock_taken, ownerdied = 0, attempt = 0;
if (refill_pi_state_cache())
return -ENOMEM;
if (time) {
to = &timeout;
hrtimer_init(&to->timer, CLOCK_REALTIME, HRTIMER_MODE_ABS);
hrtimer_init_sleeper(to, current);
to->timer.expires = *time;
}
q.pi_state = NULL;
retry:
futex_lock_mm(fshared);
ret = get_futex_key(uaddr, fshared, &q.key);
if (unlikely(ret != 0))
goto out_release_sem;
retry_unlocked:
hb = queue_lock(&q, -1, NULL);
retry_locked:
ret = lock_taken = 0;
/*
* 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 = task_pid_vnr(current);
curval = cmpxchg_futex_value_locked(uaddr, 0, newval);
if (unlikely(curval == -EFAULT))
goto uaddr_faulted;
/*
* Detect deadlocks. In case of REQUEUE_PI this is a valid
* situation and we return success to user space.
*/
if (unlikely((curval & FUTEX_TID_MASK) == task_pid_vnr(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;
/*
* Set the WAITERS flag, so the owner will know it has someone
* to wake at next unlock
*/
newval = curval | FUTEX_WAITERS;
/*
* There are two cases, where a futex might have no owner (the
* owner TID is 0): OWNER_DIED. We take over the futex in this
* case. We also do an unconditional take over, when the owner
* of the futex died.
*
* This is safe as we are protected by the hash bucket lock !
*/
if (unlikely(ownerdied || !(curval & FUTEX_TID_MASK))) {
/* Keep the OWNER_DIED bit */
newval = (curval & ~FUTEX_TID_MASK) | task_pid_vnr(current);
ownerdied = 0;
lock_taken = 1;
}
curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
if (unlikely(curval == -EFAULT))
goto uaddr_faulted;
if (unlikely(curval != uval))
goto retry_locked;
/*
* We took the lock due to owner died take over.
*/
if (unlikely(lock_taken))
goto out_unlock_release_sem;
/*
* 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.key, &q.pi_state);
if (unlikely(ret)) {
switch (ret) {
case -EAGAIN:
/*
* Task is exiting and we just wait for the
* exit to complete.
*/
queue_unlock(&q, hb);
futex_unlock_mm(fshared);
cond_resched();
goto retry;
case -ESRCH:
/*
* No owner found for this futex. Check if the
* OWNER_DIED bit is set to figure out whether
* this is a robust futex or not.
*/
if (get_futex_value_locked(&curval, uaddr))
goto uaddr_faulted;
/*
* We simply start over in case of a robust
* futex. The code above will take the futex
* and return happy.
*/
if (curval & FUTEX_OWNER_DIED) {
ownerdied = 1;
goto retry_locked;
}
default:
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.
*/
futex_unlock_mm(fshared);
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;
}
futex_lock_mm(fshared);
spin_lock(q.lock_ptr);
if (!ret) {
/*
* 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 (q.pi_state->owner != curr)
ret = fixup_pi_state_owner(uaddr, &q, curr);
} else {
/*
* Catch the rare case, where the lock was released
* when we were on the way back before we locked the
* hash bucket.
*/
if (q.pi_state->owner == curr) {
/*
* Try to get the rt_mutex now. This might
* fail as some other task acquired the
* rt_mutex after we removed ourself from the
* rt_mutex waiters list.
*/
if (rt_mutex_trylock(&q.pi_state->pi_mutex))
ret = 0;
else {
/*
* pi_state is incorrect, some other
* task did a lock steal and we
* returned due to timeout or signal
* without taking the rt_mutex. Too
* late. We can access the
* rt_mutex_owner without locking, as
* the other task is now blocked on
* the hash bucket lock. Fix the state
* up.
*/
struct task_struct *owner;
int res;
owner = rt_mutex_owner(&q.pi_state->pi_mutex);
res = fixup_pi_state_owner(uaddr, &q, owner);
WARN_ON(rt_mutex_owner(&q.pi_state->pi_mutex) !=
owner);
/* propagate -EFAULT, if the fixup failed */
if (res)
ret = res;
}
} else {
/*
* Paranoia check. If we did not take the lock
* in the trylock above, then we should not be
* the owner of the rtmutex, neither the real
* nor the pending one:
*/
if (rt_mutex_owner(&q.pi_state->pi_mutex) == curr)
printk(KERN_ERR "futex_lock_pi: ret = %d "
"pi-mutex: %p pi-state %p\n", ret,
q.pi_state->pi_mutex.owner,
q.pi_state->owner);
}
}
/* Unqueue and drop the lock */
unqueue_me_pi(&q);
futex_unlock_mm(fshared);
return ret != -EINTR ? ret : -ERESTARTNOINTR;
out_unlock_release_sem:
queue_unlock(&q, hb);
out_release_sem:
futex_unlock_mm(fshared);
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.
*
* ... and hb->lock. :-) --ANK
*/
queue_unlock(&q, hb);
if (attempt++) {
ret = futex_handle_fault((unsigned long)uaddr, fshared,
attempt);
if (ret)
goto out_release_sem;
goto retry_unlocked;
}
futex_unlock_mm(fshared);
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 rw_semaphore *fshared)
{
struct futex_hash_bucket *hb;
struct futex_q *this, *next;
u32 uval;
struct plist_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) != task_pid_vnr(current))
return -EPERM;
/*
* First take all the futex related locks:
*/
futex_lock_mm(fshared);
ret = get_futex_key(uaddr, fshared, &key);
if (unlikely(ret != 0))
goto out;
hb = hash_futex(&key);
retry_unlocked:
spin_lock(&hb->lock);
/*
* 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))
uval = cmpxchg_futex_value_locked(uaddr, task_pid_vnr(current), 0);
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 == task_pid_vnr(current)))
goto out_unlock;
/*
* Ok, other tasks may need to be woken up - check waiters
* and do the wakeup if necessary:
*/
head = &hb->chain;
plist_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:
futex_unlock_mm(fshared);
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.
*
* ... and hb->lock. --ANK
*/
spin_unlock(&hb->lock);
if (attempt++) {
ret = futex_handle_fault((unsigned long)uaddr, fshared,
attempt);
if (ret)
goto out;
uval = 0;
goto retry_unlocked;
}
futex_unlock_mm(fshared);
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);
/*
* plist_node_empty() is safe here without any lock.
* q->lock_ptr != 0 is not safe, because of ordering against wakeup.
*/
if (plist_node_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;
struct rw_semaphore *fshared;
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;
fshared = &current->mm->mmap_sem;
down_read(fshared);
err = get_futex_key(uaddr, fshared, &q->key);
if (unlikely(err != 0)) {
up_read(fshared);
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(fshared);
/* 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_vpid(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) == task_pid_vnr(curr)) {
/*
* 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 && (uval & FUTEX_WAITERS))
futex_wake(uaddr, &curr->mm->mmap_sem, 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, *next_entry, *pending;
unsigned int limit = ROBUST_LIST_LIMIT, pi, next_pi, pip;
unsigned long futex_offset;
int rc;
/*
* 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;
next_entry = NULL; /* avoid warning with gcc */
while (entry != &head->list) {
/*
* Fetch the next entry in the list before calling
* handle_futex_death:
*/
rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
/*
* 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;
if (rc)
return;
entry = next_entry;
pi = next_pi;
/*
* Avoid excessively long or circular lists:
*/
if (!--limit)
break;
cond_resched();
}
if (pending)
handle_futex_death((void __user *)pending + futex_offset,
curr, pip);
}
long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
u32 __user *uaddr2, u32 val2, u32 val3)
{
int ret;
int cmd = op & FUTEX_CMD_MASK;
struct rw_semaphore *fshared = NULL;
if (!(op & FUTEX_PRIVATE_FLAG))
fshared = &current->mm->mmap_sem;
switch (cmd) {
case FUTEX_WAIT:
ret = futex_wait(uaddr, fshared, val, timeout);
break;
case FUTEX_WAKE:
ret = futex_wake(uaddr, fshared, 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, fshared, uaddr2, val, val2, NULL);
break;
case FUTEX_CMP_REQUEUE:
ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, &val3);
break;
case FUTEX_WAKE_OP:
ret = futex_wake_op(uaddr, fshared, uaddr2, val, val2, val3);
break;
case FUTEX_LOCK_PI:
ret = futex_lock_pi(uaddr, fshared, val, timeout, 0);
break;
case FUTEX_UNLOCK_PI:
ret = futex_unlock_pi(uaddr, fshared);
break;
case FUTEX_TRYLOCK_PI:
ret = futex_lock_pi(uaddr, fshared, 0, timeout, 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 ts;
ktime_t t, *tp = NULL;
u32 val2 = 0;
int cmd = op & FUTEX_CMD_MASK;
if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI)) {
if (copy_from_user(&ts, utime, sizeof(ts)) != 0)
return -EFAULT;
if (!timespec_valid(&ts))
return -EINVAL;
t = timespec_to_ktime(ts);
if (cmd == FUTEX_WAIT)
t = ktime_add(ktime_get(), t);
tp = &t;
}
/*
* requeue parameter in 'utime' if cmd == FUTEX_REQUEUE.
* number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
*/
if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
cmd == FUTEX_WAKE_OP)
val2 = (u32) (unsigned long) utime;
return do_futex(uaddr, op, val, tp, 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, FUTEXFS_SUPER_MAGIC, 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++) {
plist_head_init(&futex_queues[i].chain, &futex_queues[i].lock);
spin_lock_init(&futex_queues[i].lock);
}
return 0;
}
__initcall(init);