| /* |
| * 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. |
| * |
| * 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> |
| |
| #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; |
| }; |
| |
| /* |
| * 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; |
| }; |
| |
| /* |
| * 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_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_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; |
| |
| inc_preempt_count(); |
| ret = __copy_from_user_inatomic(dest, from, sizeof(u32)); |
| dec_preempt_count(); |
| |
| return ret ? -EFAULT : 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. |
| */ |
| wmb(); |
| q->lock_ptr = NULL; |
| } |
| |
| /* |
| * 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)) { |
| 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: |
| if (hb1 < hb2) |
| spin_lock(&hb1->lock); |
| spin_lock(&hb2->lock); |
| if (hb1 > hb2) |
| spin_lock(&hb1->lock); |
| |
| 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++) { |
| struct vm_area_struct * vma; |
| struct mm_struct *mm = current->mm; |
| unsigned long address = (unsigned long)uaddr2; |
| |
| ret = -EFAULT; |
| if (attempt >= 2 || |
| !(vma = find_vma(mm, address)) || |
| vma->vm_start > address || |
| !(vma->vm_flags & VM_WRITE)) |
| goto out; |
| |
| 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: |
| 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); |
| |
| if (hb1 < hb2) |
| spin_lock(&hb1->lock); |
| spin_lock(&hb2->lock); |
| if (hb1 > hb2) |
| spin_lock(&hb1->lock); |
| |
| 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 { |
| 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; |
| /* Make sure to stop if key1 == key2: */ |
| if (head1 == &hb2->chain && head1 != &next->list) |
| head1 = &this->list; |
| } |
| } |
| |
| 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); |
| 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; |
| 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); |
| spin_unlock(lock_ptr); |
| ret = 1; |
| } |
| |
| drop_key_refs(&q->key); |
| return ret; |
| } |
| |
| static int futex_wait(u32 __user *uaddr, u32 val, unsigned long time) |
| { |
| DECLARE_WAITQUEUE(wait, current); |
| struct futex_hash_bucket *hb; |
| struct futex_q q; |
| u32 uval; |
| int ret; |
| |
| retry: |
| down_read(¤t->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(¤t->mm->mmap_sem); |
| |
| ret = get_user(uval, uaddr); |
| |
| if (!ret) |
| goto retry; |
| return ret; |
| } |
| if (uval != val) { |
| ret = -EWOULDBLOCK; |
| queue_unlock(&q, hb); |
| goto out_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(¤t->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_release_sem: |
| up_read(¤t->mm->mmap_sem); |
| 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 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; |
| |
| 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_vfsmnt = mntget(futex_mnt); |
| filp->f_dentry = dget(futex_mnt->mnt_root); |
| filp->f_mapping = filp->f_dentry->d_inode->i_mapping; |
| |
| if (signal) { |
| err = f_setown(filp, current->pid, 1); |
| if (err < 0) { |
| goto error; |
| } |
| filp->f_owner.signum = signal; |
| } |
| |
| q = kmalloc(sizeof(*q), GFP_KERNEL); |
| if (!q) { |
| err = -ENOMEM; |
| goto error; |
| } |
| |
| 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_DEAD 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 **head_ptr, |
| size_t __user *len_ptr) |
| { |
| struct robust_list_head *head; |
| unsigned long ret; |
| |
| if (!pid) |
| head = current->robust_list; |
| else { |
| struct task_struct *p; |
| |
| ret = -ESRCH; |
| read_lock(&tasklist_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; |
| read_unlock(&tasklist_lock); |
| } |
| |
| if (put_user(sizeof(*head), len_ptr)) |
| return -EFAULT; |
| return put_user(head, head_ptr); |
| |
| err_unlock: |
| read_unlock(&tasklist_lock); |
| |
| 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) |
| { |
| u32 uval; |
| |
| 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. |
| */ |
| if (futex_atomic_cmpxchg_inatomic(uaddr, uval, |
| uval | FUTEX_OWNER_DIED) != uval) |
| goto retry; |
| |
| if (uval & FUTEX_WAITERS) |
| futex_wake(uaddr, 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; |
| unsigned long futex_offset; |
| |
| /* |
| * Fetch the list head (which was registered earlier, via |
| * sys_set_robust_list()): |
| */ |
| if (get_user(entry, &head->list.next)) |
| 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 (get_user(pending, &head->list_op_pending)) |
| return; |
| if (pending) |
| handle_futex_death((void *)pending + futex_offset, curr); |
| |
| while (entry != &head->list) { |
| /* |
| * A pending lock might already be on the list, so |
| * dont process it twice: |
| */ |
| if (entry != pending) |
| if (handle_futex_death((void *)entry + futex_offset, |
| curr)) |
| return; |
| /* |
| * Fetch the next entry in the list: |
| */ |
| if (get_user(entry, &entry->next)) |
| 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; |
| 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)) { |
| if (copy_from_user(&t, utime, sizeof(t)) != 0) |
| return -EFAULT; |
| if (!timespec_valid(&t)) |
| return -EINVAL; |
| timeout = timespec_to_jiffies(&t) + 1; |
| } |
| /* |
| * requeue parameter in 'utime' if op == FUTEX_REQUEUE. |
| */ |
| if (op >= FUTEX_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) |
| { |
| unsigned int i; |
| |
| register_filesystem(&futex_fs_type); |
| futex_mnt = kern_mount(&futex_fs_type); |
| |
| 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); |