diff options
Diffstat (limited to 'kernel/futex.c')
| -rw-r--r-- | kernel/futex.c | 2099 |
1 files changed, 2099 insertions, 0 deletions
diff --git a/kernel/futex.c b/kernel/futex.c new file mode 100644 index 0000000..c14b159 --- /dev/null +++ b/kernel/futex.c @@ -0,0 +1,2099 @@ +/* + * 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" + +int __read_mostly futex_cmpxchg_enabled; + +#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; + + /* Optional priority inheritance state: */ + struct futex_pi_state *pi_state; + struct task_struct *task; + + /* Bitset for the optional bitmasked wakeup */ + u32 bitset; +}; + +/* + * 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]; + +/* + * 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, + * ¤t->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 ¤t->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 == NULL) + 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; + + if (!futex_cmpxchg_enabled) + return; + /* + * 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); + /* + * 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, u32 bitset) +{ + struct futex_hash_bucket *hb; + struct futex_q *this, *next; + struct plist_head *head; + union futex_key key; + int ret; + + if (!bitset) + return -EINVAL; + + 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; + } + + /* Check if one of the bits is set in both bitsets */ + if (!(this->bitset & bitset)) + continue; + + 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) +{ + struct futex_hash_bucket *hb; + + 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. + */ + +/* 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, + struct rw_semaphore *fshared) +{ + u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS; + struct futex_pi_state *pi_state = q->pi_state; + struct task_struct *oldowner = pi_state->owner; + u32 uval, curval, newval; + int ret, attempt = 0; + + /* Owner died? */ + if (!pi_state->owner) + newtid |= FUTEX_OWNER_DIED; + + /* + * We are here either because we stole the rtmutex from the + * pending owner or we are the pending owner which failed to + * get the rtmutex. We have to replace the pending owner TID + * in the user space variable. This must be atomic as we have + * to preserve the owner died bit here. + * + * Note: We write the user space value _before_ changing the + * pi_state because we can fault here. Imagine swapped out + * pages or a fork, which was running right before we acquired + * mmap_sem, that marked all the anonymous memory readonly for + * cow. + * + * Modifying pi_state _before_ the user space value would + * leave the pi_state in an inconsistent state when we fault + * here, because we need to drop the hash bucket lock to + * handle the fault. This might be observed in the PID check + * in lookup_pi_state. + */ +retry: + if (get_futex_value_locked(&uval, uaddr)) + goto handle_fault; + + while (1) { + newval = (uval & FUTEX_OWNER_DIED) | newtid; + + curval = cmpxchg_futex_value_locked(uaddr, uval, newval); + + if (curval == -EFAULT) + goto handle_fault; + if (curval == uval) + break; + uval = curval; + } + + /* + * We fixed up user space. Now we need to fix the pi_state + * itself. + */ + 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); + } + + 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); + return 0; + + /* + * To handle the page fault we need to drop the hash bucket + * lock here. That gives the other task (either the pending + * owner itself or the task which stole the rtmutex) the + * chance to try the fixup of the pi_state. So once we are + * back from handling the fault we need to check the pi_state + * after reacquiring the hash bucket lock and before trying to + * do another fixup. When the fixup has been done already we + * simply return. + */ +handle_fault: + spin_unlock(q->lock_ptr); + + ret = futex_handle_fault((unsigned long)uaddr, fshared, attempt++); + + spin_lock(q->lock_ptr); + + /* + * Check if someone else fixed it for us: + */ + if (pi_state->owner != oldowner) + return 0; + + if (ret) + return ret; + + goto retry; +} + +/* + * 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, u32 bitset) +{ + 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; + + if (!bitset) + return -EINVAL; + + q.pi_state = NULL; + q.bitset = bitset; + 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); + + /* + * 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 { + unsigned long slack; + slack = current->timer_slack_ns; + if (rt_task(current)) + slack = 0; + hrtimer_init_on_stack(&t.timer, CLOCK_MONOTONIC, + HRTIMER_MODE_ABS); + hrtimer_init_sleeper(&t, current); + hrtimer_set_expires_range_ns(&t.timer, *abs_time, slack); + + hrtimer_start_expires(&t.timer, HRTIMER_MODE_ABS); + if (!hrtimer_active(&t.timer)) + t.task = NULL; + + /* + * 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); + + destroy_hrtimer_on_stack(&t.timer); + } + } + __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 = ¤t_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.bitset = bitset; + 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 = ¤t->mm->mmap_sem; + return (long)futex_wait(uaddr, fshared, restart->futex.val, &t, + restart->futex.bitset); +} + + +/* + * 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_on_stack(&to->timer, CLOCK_REALTIME, + HRTIMER_MODE_ABS); + hrtimer_init_sleeper(to, current); + hrtimer_set_expires(&to->timer, *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); + + 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, fshared); + } 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, + fshared); + + /* 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); + + if (to) + destroy_hrtimer_on_stack(&to->timer); + return ret != -EINTR ? ret : -ERESTARTNOINTR; + + out_unlock_release_sem: + queue_unlock(&q, hb); + + out_release_sem: + futex_unlock_mm(fshared); + if (to) + destroy_hrtimer_on_stack(&to->timer); + 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; + + if (to) + destroy_hrtimer_on_stack(&to->timer); + 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; +} + +/* + * 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 + */ +SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head, + size_t, len) +{ + if (!futex_cmpxchg_enabled) + return -ENOSYS; + /* + * 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 + */ +SYSCALL_DEFINE3(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 (!futex_cmpxchg_enabled) + return -ENOSYS; + + 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, + FUTEX_BITSET_MATCH_ANY); + } + 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; + + if (!futex_cmpxchg_enabled) + return; + + /* + * 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 = -ENOSYS; + int cmd = op & FUTEX_CMD_MASK; + struct rw_semaphore *fshared = NULL; + + if (!(op & FUTEX_PRIVATE_FLAG)) + fshared = ¤t->mm->mmap_sem; + + switch (cmd) { + case FUTEX_WAIT: + val3 = FUTEX_BITSET_MATCH_ANY; + case FUTEX_WAIT_BITSET: + ret = futex_wait(uaddr, fshared, val, timeout, val3); + break; + case FUTEX_WAKE: + val3 = FUTEX_BITSET_MATCH_ANY; + case FUTEX_WAKE_BITSET: + ret = futex_wake(uaddr, fshared, val, val3); + 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: + if (futex_cmpxchg_enabled) + ret = futex_lock_pi(uaddr, fshared, val, timeout, 0); + break; + case FUTEX_UNLOCK_PI: + if (futex_cmpxchg_enabled) + ret = futex_unlock_pi(uaddr, fshared); + break; + case FUTEX_TRYLOCK_PI: + if (futex_cmpxchg_enabled) + ret = futex_lock_pi(uaddr, fshared, 0, timeout, 1); + break; + default: + ret = -ENOSYS; + } + return ret; +} + + +SYSCALL_DEFINE6(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 || + cmd == FUTEX_WAIT_BITSET)) { + 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_safe(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 __init futex_init(void) +{ + u32 curval; + int i; + + /* + * This will fail and we want it. Some arch implementations do + * runtime detection of the futex_atomic_cmpxchg_inatomic() + * functionality. We want to know that before we call in any + * of the complex code paths. Also we want to prevent + * registration of robust lists in that case. NULL is + * guaranteed to fault and we get -EFAULT on functional + * implementation, the non functional ones will return + * -ENOSYS. + */ + curval = cmpxchg_futex_value_locked(NULL, 0, 0); + if (curval == -EFAULT) + futex_cmpxchg_enabled = 1; + + 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(futex_init); |
