X-Git-Url: http://git.onelab.eu/?a=blobdiff_plain;f=kernel%2Ffutex.c;h=9d260e838cffdca6f951d6625626ab9d62f19d81;hb=3967a72a825e44bff5d10f516e90b6f59f59e599;hp=9a25d76bd6bd9aa13b9f74be1c0778ffe99c6039;hpb=9bf4aaab3e101692164d49b7ca357651eb691cb6;p=linux-2.6.git diff --git a/kernel/futex.c b/kernel/futex.c index 9a25d76bd..9d260e838 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -6,7 +6,15 @@ * (C) Copyright 2003 Red Hat Inc, All Rights Reserved * * Removed page pinning, fix privately mapped COW pages and other cleanups - * (C) Copyright 2003 Jamie Lokier + * (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 + * Copyright (C) 2006 Timesys Corp., Thomas Gleixner * * Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly * enough at me, Linus for the original (flawed) idea, Matthew @@ -39,8 +47,12 @@ #include #include #include +#include +#include -#define FUTEX_HASHBITS 8 +#include "rtmutex_common.h" + +#define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8) /* * Futexes are matched on equal values of this key. @@ -57,7 +69,7 @@ union futex_key { int offset; } shared; struct { - unsigned long uaddr; + unsigned long address; struct mm_struct *mm; int offset; } private; @@ -68,6 +80,27 @@ union futex_key { } 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). @@ -81,15 +114,19 @@ struct futex_q { struct list_head list; wait_queue_head_t waiters; - /* Which hash list lock to use. */ + /* Which hash list lock to use: */ spinlock_t *lock_ptr; - /* Key which the futex is hashed on. */ + /* Key which the futex is hashed on: */ union futex_key key; - /* For fd, sigio sent using these. */ + /* 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; }; /* @@ -97,7 +134,6 @@ struct futex_q { */ struct futex_hash_bucket { spinlock_t lock; - unsigned int nqueued; struct list_head chain; }; @@ -139,8 +175,9 @@ static inline int match_futex(union futex_key *key1, union futex_key *key2) * * Should be called with ¤t->mm->mmap_sem but NOT any spinlocks. */ -static int get_futex_key(unsigned long uaddr, union futex_key *key) +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; @@ -149,16 +186,16 @@ static int get_futex_key(unsigned long uaddr, union futex_key *key) /* * The futex address must be "naturally" aligned. */ - key->both.offset = uaddr % PAGE_SIZE; + key->both.offset = address % PAGE_SIZE; if (unlikely((key->both.offset % sizeof(u32)) != 0)) return -EINVAL; - uaddr -= key->both.offset; + 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, uaddr); + vma = find_extend_vma(mm, address); if (unlikely(!vma)) return -EFAULT; @@ -179,7 +216,7 @@ static int get_futex_key(unsigned long uaddr, union futex_key *key) */ if (likely(!(vma->vm_flags & VM_MAYSHARE))) { key->private.mm = mm; - key->private.uaddr = uaddr; + key->private.address = address; return 0; } @@ -189,7 +226,7 @@ static int get_futex_key(unsigned long uaddr, union futex_key *key) 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 = (((uaddr - vma->vm_start) >> PAGE_SHIFT) + key->shared.pgoff = (((address - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff); return 0; } @@ -200,24 +237,7 @@ static int get_futex_key(unsigned long uaddr, union futex_key *key) * from swap. But that's a lot of code to duplicate here * for a rare case, so we simply fetch the page. */ - - /* - * Do a quick atomic lookup first - this is the fastpath. - */ - spin_lock(¤t->mm->page_table_lock); - page = follow_page(mm, uaddr, 0); - if (likely(page != NULL)) { - key->shared.pgoff = - page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT); - spin_unlock(¤t->mm->page_table_lock); - return 0; - } - spin_unlock(¤t->mm->page_table_lock); - - /* - * Do it the general way. - */ - err = get_user_pages(current, mm, uaddr, 1, 0, 0, &page, NULL); + 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); @@ -258,6 +278,258 @@ static void drop_key_refs(union futex_key *key) } } +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; +} + +/* + * 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 = kmalloc(sizeof(*pi_state), GFP_KERNEL); + + if (!pi_state) + return -ENOMEM; + + memset(pi_state, 0, sizeof(*pi_state)); + 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; + + read_lock(&tasklist_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: + read_unlock(&tasklist_lock); + + 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. @@ -275,20 +547,115 @@ static void wake_futex(struct futex_q *q) /* * 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; } +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; + + inc_preempt_count(); + curval = futex_atomic_cmpxchg_inatomic(uaddr, uval, newval); + dec_preempt_count(); + 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: + */ + inc_preempt_count(); + oldval = futex_atomic_cmpxchg_inatomic(uaddr, uval, 0); + dec_preempt_count(); + + 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(unsigned long uaddr, int nr_wake) +static int futex_wake(u32 __user *uaddr, int nr_wake) { - union futex_key key; - struct futex_hash_bucket *bh; - struct list_head *head; + 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); @@ -297,19 +664,136 @@ static int futex_wake(unsigned long uaddr, int nr_wake) if (unlikely(ret != 0)) goto out; - bh = hash_futex(&key); - spin_lock(&bh->lock); - head = &bh->chain; + 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; } } - spin_unlock(&bh->lock); + 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; @@ -319,16 +803,16 @@ out: * Requeue all waiters hashed on one physical page to another * physical page. */ -static int futex_requeue(unsigned long uaddr1, unsigned long uaddr2, - int nr_wake, int nr_requeue, int *valp) +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 *bh1, *bh2; + struct futex_hash_bucket *hb1, *hb2; struct list_head *head1; struct futex_q *this, *next; int ret, drop_count = 0; - unsigned int nqueued; + retry: down_read(¤t->mm->mmap_sem); ret = get_futex_key(uaddr1, &key1); @@ -338,69 +822,68 @@ static int futex_requeue(unsigned long uaddr1, unsigned long uaddr2, if (unlikely(ret != 0)) goto out; - bh1 = hash_futex(&key1); - bh2 = hash_futex(&key2); + hb1 = hash_futex(&key1); + hb2 = hash_futex(&key2); - nqueued = bh1->nqueued; - if (likely(valp != NULL)) { - int curval; + double_lock_hb(hb1, hb2); - /* In order to avoid doing get_user while - holding bh1->lock and bh2->lock, nqueued - (monotonically increasing field) must be first - read, then *uaddr1 fetched from userland and - after acquiring lock nqueued field compared with - the stored value. The smp_mb () below - makes sure that bh1->nqueued is read from memory - before *uaddr1. */ - smp_mb(); + if (likely(cmpval != NULL)) { + u32 curval; - if (get_user(curval, (int __user *)uaddr1) != 0) { - ret = -EFAULT; - goto out; + 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 != *valp) { + if (curval != *cmpval) { ret = -EAGAIN; - goto out; + goto out_unlock; } } - if (bh1 < bh2) - spin_lock(&bh1->lock); - spin_lock(&bh2->lock); - if (bh1 > bh2) - spin_lock(&bh1->lock); - - if (unlikely(nqueued != bh1->nqueued && valp != NULL)) { - ret = -EAGAIN; - goto out_unlock; - } - - head1 = &bh1->chain; + 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, &bh2->chain); - this->lock_ptr = &bh2->lock; + /* + * 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; - /* Make sure to stop if key1 == key2 */ - if (head1 == &bh2->chain && head1 != &next->list) - head1 = &this->list; } } out_unlock: - spin_unlock(&bh1->lock); - if (bh1 != bh2) - spin_unlock(&bh2->lock); + spin_unlock(&hb1->lock); + if (hb1 != hb2) + spin_unlock(&hb2->lock); /* drop_key_refs() must be called outside the spinlocks. */ while (--drop_count >= 0) @@ -411,15 +894,11 @@ out: return ret; } -/* - * 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) +static inline struct futex_hash_bucket * +queue_lock(struct futex_q *q, int fd, struct file *filp) { - struct futex_hash_bucket *bh; + struct futex_hash_bucket *hb; q->fd = fd; q->filp = filp; @@ -427,24 +906,51 @@ static void queue_me(struct futex_q *q, int fd, struct file *filp) init_waitqueue_head(&q->waiters); get_key_refs(&q->key); - bh = hash_futex(&q->key); - q->lock_ptr = &bh->lock; + hb = hash_futex(&q->key); + q->lock_ptr = &hb->lock; - spin_lock(&bh->lock); - bh->nqueued++; - list_add_tail(&q->list, &bh->chain); - spin_unlock(&bh->lock); + spin_lock(&hb->lock); + return hb; } -/* Return 1 if we were still queued (ie. 0 means we were woken) */ -static int unqueue_me(struct futex_q *q) +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) { - int ret = 0; 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); /* @@ -466,6 +972,9 @@ static int unqueue_me(struct futex_q *q) } WARN_ON(list_empty(&q->list)); list_del(&q->list); + + BUG_ON(q->pi_state); + spin_unlock(lock_ptr); ret = 1; } @@ -474,39 +983,92 @@ static int unqueue_me(struct futex_q *q) return ret; } -static int futex_wait(unsigned long uaddr, int val, unsigned long time) +/* + * 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) { - DECLARE_WAITQUEUE(wait, current); - int ret, curval; + 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; - down_read(¤t->mm->mmap_sem); + 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; - queue_me(&q, -1, NULL); + hb = queue_lock(&q, -1, NULL); /* - * Access the page after the futex is queued. + * 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. + * since we looked it up in get_futex_key. */ - if (get_user(curval, (int __user *)uaddr) != 0) { - ret = -EFAULT; - goto out_unqueue; - } - if (curval != val) { - ret = -EWOULDBLOCK; - goto out_unqueue; + 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(¤t->mm->mmap_sem); + */ + up_read(&curr->mm->mmap_sem); /* * There might have been scheduling since the queue_me(), as we @@ -538,16 +1100,367 @@ static int futex_wait(unsigned long uaddr, int val, unsigned long time) return 0; if (time == 0) return -ETIMEDOUT; - /* A spurious wakeup should never happen. */ - WARN_ON(!signal_pending(current)); + /* + * We expect signal_pending(current), but another thread may + * have handled it for us already. + */ return -EINTR; - out_unqueue: - /* If we were woken (and unqueued), we succeeded, whatever. */ - if (!unqueue_me(&q)) - ret = 0; + 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; + + inc_preempt_count(); + curval = futex_atomic_cmpxchg_inatomic(uaddr, 0, newval); + dec_preempt_count(); + + 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; + + inc_preempt_count(); + curval = futex_atomic_cmpxchg_inatomic(uaddr, uval, newval); + dec_preempt_count(); + + 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; + + inc_preempt_count(); + curval = futex_atomic_cmpxchg_inatomic(uaddr, + uval, newval); + dec_preempt_count(); + + 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)) { + inc_preempt_count(); + uval = futex_atomic_cmpxchg_inatomic(uaddr, current->pid, 0); + dec_preempt_count(); + } + + 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; } @@ -557,6 +1470,7 @@ static int futex_close(struct inode *inode, struct file *filp) unqueue_me(q); kfree(q); + return 0; } @@ -588,14 +1502,14 @@ static struct file_operations futex_fops = { * Signal allows caller to avoid the race which would occur if they * set the sigio stuff up afterwards. */ -static int futex_fd(unsigned long uaddr, int signal) +static int futex_fd(u32 __user *uaddr, int signal) { struct futex_q *q; struct file *filp; int ret, err; ret = -EINVAL; - if (signal < 0 || signal > _NSIG) + if (!valid_signal(signal)) goto out; ret = get_unused_fd(); @@ -613,34 +1527,27 @@ static int futex_fd(unsigned long uaddr, int signal) filp->f_mapping = filp->f_dentry->d_inode->i_mapping; if (signal) { - int err; err = f_setown(filp, current->pid, 1); if (err < 0) { - put_unused_fd(ret); - put_filp(filp); - ret = err; - goto out; + goto error; } filp->f_owner.signum = signal; } q = kmalloc(sizeof(*q), GFP_KERNEL); if (!q) { - put_unused_fd(ret); - put_filp(filp); - ret = -ENOMEM; - goto out; + 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); - put_unused_fd(ret); - put_filp(filp); kfree(q); - return err; + goto error; } /* @@ -656,10 +1563,210 @@ static int futex_fd(unsigned long uaddr, int signal) fd_install(ret, filp); out: return ret; +error: + put_unused_fd(ret); + put_filp(filp); + ret = err; + goto out; } -long do_futex(unsigned long uaddr, int op, int val, unsigned long timeout, - unsigned long uaddr2, int val2, int val3) +/* + * 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 **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, 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 **head, int *pi) +{ + unsigned long uentry; + + if (get_user(uentry, (unsigned long *)head)) + return -EFAULT; + + *entry = (void *)(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 *)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 *)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; @@ -680,6 +1787,18 @@ long do_futex(unsigned long uaddr, int op, int val, unsigned long timeout, 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; } @@ -687,34 +1806,40 @@ long do_futex(unsigned long uaddr, int op, int val, unsigned long timeout, } -asmlinkage long sys_futex(u32 __user *uaddr, int op, int val, +asmlinkage long sys_futex(u32 __user *uaddr, int op, u32 val, struct timespec __user *utime, u32 __user *uaddr2, - int val3) + u32 val3) { struct timespec t; unsigned long timeout = MAX_SCHEDULE_TIMEOUT; - int val2 = 0; + u32 val2 = 0; - if ((op == FUTEX_WAIT) && utime) { + if (utime && (op == FUTEX_WAIT || op == FUTEX_LOCK_PI)) { if (copy_from_user(&t, utime, sizeof(t)) != 0) return -EFAULT; - timeout = timespec_to_jiffies(&t) + 1; + 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) - val2 = (int) (unsigned long) utime; + if (op == FUTEX_REQUEUE || op == FUTEX_CMP_REQUEUE) + val2 = (u32) (unsigned long) utime; - return do_futex((unsigned long)uaddr, op, val, timeout, - (unsigned long)uaddr2, val2, val3); + return do_futex(uaddr, op, val, timeout, uaddr2, val2, val3); } -static struct super_block * -futexfs_get_sb(struct file_system_type *fs_type, - int flags, const char *dev_name, void *data) +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); + return get_sb_pseudo(fs_type, "futex", NULL, 0xBAD1DEA, mnt); } static struct file_system_type futex_fs_type = { @@ -732,7 +1857,7 @@ static int __init init(void) for (i = 0; i < ARRAY_SIZE(futex_queues); i++) { INIT_LIST_HEAD(&futex_queues[i].chain); - futex_queues[i].lock = SPIN_LOCK_UNLOCKED; + spin_lock_init(&futex_queues[i].lock); } return 0; }