1086 lines
26 KiB
C
1086 lines
26 KiB
C
/*
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* Fast Userspace Mutexes (which I call "Futexes!").
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* (C) Rusty Russell, IBM 2002
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*
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* Generalized futexes, futex requeueing, misc fixes by Ingo Molnar
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* (C) Copyright 2003 Red Hat Inc, All Rights Reserved
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*
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* Removed page pinning, fix privately mapped COW pages and other cleanups
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* (C) Copyright 2003, 2004 Jamie Lokier
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*
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* Robust futex support started by Ingo Molnar
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* (C) Copyright 2006 Red Hat Inc, All Rights Reserved
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* Thanks to Thomas Gleixner for suggestions, analysis and fixes.
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*
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* Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly
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* enough at me, Linus for the original (flawed) idea, Matthew
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* Kirkwood for proof-of-concept implementation.
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*
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* "The futexes are also cursed."
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* "But they come in a choice of three flavours!"
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*/
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#include <linux/slab.h>
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#include <linux/poll.h>
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#include <linux/fs.h>
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#include <linux/file.h>
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#include <linux/jhash.h>
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#include <linux/init.h>
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#include <linux/futex.h>
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#include <linux/mount.h>
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#include <linux/pagemap.h>
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#include <linux/syscalls.h>
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#include <linux/signal.h>
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#include <asm/futex.h>
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#define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8)
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/*
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* Futexes are matched on equal values of this key.
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* The key type depends on whether it's a shared or private mapping.
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* Don't rearrange members without looking at hash_futex().
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*
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* offset is aligned to a multiple of sizeof(u32) (== 4) by definition.
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* We set bit 0 to indicate if it's an inode-based key.
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*/
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union futex_key {
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struct {
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unsigned long pgoff;
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struct inode *inode;
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int offset;
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} shared;
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struct {
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unsigned long uaddr;
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struct mm_struct *mm;
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int offset;
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} private;
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struct {
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unsigned long word;
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void *ptr;
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int offset;
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} both;
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};
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/*
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* We use this hashed waitqueue instead of a normal wait_queue_t, so
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* we can wake only the relevant ones (hashed queues may be shared).
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*
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* A futex_q has a woken state, just like tasks have TASK_RUNNING.
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* It is considered woken when list_empty(&q->list) || q->lock_ptr == 0.
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* The order of wakup is always to make the first condition true, then
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* wake up q->waiters, then make the second condition true.
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*/
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struct futex_q {
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struct list_head list;
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wait_queue_head_t waiters;
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/* Which hash list lock to use. */
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spinlock_t *lock_ptr;
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/* Key which the futex is hashed on. */
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union futex_key key;
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/* For fd, sigio sent using these. */
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int fd;
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struct file *filp;
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};
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/*
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* Split the global futex_lock into every hash list lock.
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*/
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struct futex_hash_bucket {
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spinlock_t lock;
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struct list_head chain;
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};
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static struct futex_hash_bucket futex_queues[1<<FUTEX_HASHBITS];
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/* Futex-fs vfsmount entry: */
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static struct vfsmount *futex_mnt;
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/*
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* We hash on the keys returned from get_futex_key (see below).
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*/
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static struct futex_hash_bucket *hash_futex(union futex_key *key)
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{
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u32 hash = jhash2((u32*)&key->both.word,
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(sizeof(key->both.word)+sizeof(key->both.ptr))/4,
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key->both.offset);
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return &futex_queues[hash & ((1 << FUTEX_HASHBITS)-1)];
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}
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/*
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* Return 1 if two futex_keys are equal, 0 otherwise.
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*/
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static inline int match_futex(union futex_key *key1, union futex_key *key2)
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{
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return (key1->both.word == key2->both.word
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&& key1->both.ptr == key2->both.ptr
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&& key1->both.offset == key2->both.offset);
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}
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/*
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* Get parameters which are the keys for a futex.
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*
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* For shared mappings, it's (page->index, vma->vm_file->f_dentry->d_inode,
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* offset_within_page). For private mappings, it's (uaddr, current->mm).
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* We can usually work out the index without swapping in the page.
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*
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* Returns: 0, or negative error code.
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* The key words are stored in *key on success.
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*
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* Should be called with ¤t->mm->mmap_sem but NOT any spinlocks.
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*/
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static int get_futex_key(unsigned long uaddr, union futex_key *key)
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{
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struct mm_struct *mm = current->mm;
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struct vm_area_struct *vma;
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struct page *page;
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int err;
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/*
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* The futex address must be "naturally" aligned.
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*/
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key->both.offset = uaddr % PAGE_SIZE;
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if (unlikely((key->both.offset % sizeof(u32)) != 0))
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return -EINVAL;
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uaddr -= key->both.offset;
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/*
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* The futex is hashed differently depending on whether
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* it's in a shared or private mapping. So check vma first.
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*/
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vma = find_extend_vma(mm, uaddr);
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if (unlikely(!vma))
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return -EFAULT;
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/*
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* Permissions.
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*/
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if (unlikely((vma->vm_flags & (VM_IO|VM_READ)) != VM_READ))
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return (vma->vm_flags & VM_IO) ? -EPERM : -EACCES;
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/*
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* Private mappings are handled in a simple way.
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*
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* NOTE: When userspace waits on a MAP_SHARED mapping, even if
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* it's a read-only handle, it's expected that futexes attach to
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* the object not the particular process. Therefore we use
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* VM_MAYSHARE here, not VM_SHARED which is restricted to shared
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* mappings of _writable_ handles.
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*/
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if (likely(!(vma->vm_flags & VM_MAYSHARE))) {
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key->private.mm = mm;
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key->private.uaddr = uaddr;
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return 0;
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}
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/*
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* Linear file mappings are also simple.
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*/
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key->shared.inode = vma->vm_file->f_dentry->d_inode;
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key->both.offset++; /* Bit 0 of offset indicates inode-based key. */
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if (likely(!(vma->vm_flags & VM_NONLINEAR))) {
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key->shared.pgoff = (((uaddr - vma->vm_start) >> PAGE_SHIFT)
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+ vma->vm_pgoff);
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return 0;
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}
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/*
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* We could walk the page table to read the non-linear
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* pte, and get the page index without fetching the page
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* from swap. But that's a lot of code to duplicate here
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* for a rare case, so we simply fetch the page.
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*/
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err = get_user_pages(current, mm, uaddr, 1, 0, 0, &page, NULL);
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if (err >= 0) {
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key->shared.pgoff =
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page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
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put_page(page);
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return 0;
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}
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return err;
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}
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/*
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* Take a reference to the resource addressed by a key.
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* Can be called while holding spinlocks.
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*
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* NOTE: mmap_sem MUST be held between get_futex_key() and calling this
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* function, if it is called at all. mmap_sem keeps key->shared.inode valid.
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*/
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static inline void get_key_refs(union futex_key *key)
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{
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if (key->both.ptr != 0) {
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if (key->both.offset & 1)
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atomic_inc(&key->shared.inode->i_count);
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else
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atomic_inc(&key->private.mm->mm_count);
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}
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}
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/*
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* Drop a reference to the resource addressed by a key.
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* The hash bucket spinlock must not be held.
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*/
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static void drop_key_refs(union futex_key *key)
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{
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if (key->both.ptr != 0) {
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if (key->both.offset & 1)
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iput(key->shared.inode);
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else
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mmdrop(key->private.mm);
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}
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}
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static inline int get_futex_value_locked(int *dest, int __user *from)
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{
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int ret;
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inc_preempt_count();
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ret = __copy_from_user_inatomic(dest, from, sizeof(int));
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dec_preempt_count();
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return ret ? -EFAULT : 0;
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}
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/*
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* The hash bucket lock must be held when this is called.
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* Afterwards, the futex_q must not be accessed.
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*/
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static void wake_futex(struct futex_q *q)
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{
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list_del_init(&q->list);
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if (q->filp)
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send_sigio(&q->filp->f_owner, q->fd, POLL_IN);
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/*
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* The lock in wake_up_all() is a crucial memory barrier after the
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* list_del_init() and also before assigning to q->lock_ptr.
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*/
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wake_up_all(&q->waiters);
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/*
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* The waiting task can free the futex_q as soon as this is written,
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* without taking any locks. This must come last.
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*
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* A memory barrier is required here to prevent the following store
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* to lock_ptr from getting ahead of the wakeup. Clearing the lock
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* at the end of wake_up_all() does not prevent this store from
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* moving.
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*/
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wmb();
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q->lock_ptr = NULL;
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}
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/*
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* Wake up all waiters hashed on the physical page that is mapped
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* to this virtual address:
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*/
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static int futex_wake(unsigned long uaddr, int nr_wake)
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{
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union futex_key key;
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struct futex_hash_bucket *bh;
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struct list_head *head;
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struct futex_q *this, *next;
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int ret;
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down_read(¤t->mm->mmap_sem);
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ret = get_futex_key(uaddr, &key);
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if (unlikely(ret != 0))
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goto out;
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bh = hash_futex(&key);
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spin_lock(&bh->lock);
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head = &bh->chain;
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list_for_each_entry_safe(this, next, head, list) {
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if (match_futex (&this->key, &key)) {
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wake_futex(this);
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if (++ret >= nr_wake)
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break;
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}
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}
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spin_unlock(&bh->lock);
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out:
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up_read(¤t->mm->mmap_sem);
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return ret;
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}
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/*
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* Wake up all waiters hashed on the physical page that is mapped
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* to this virtual address:
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*/
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static int futex_wake_op(unsigned long uaddr1, unsigned long uaddr2, int nr_wake, int nr_wake2, int op)
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{
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union futex_key key1, key2;
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struct futex_hash_bucket *bh1, *bh2;
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struct list_head *head;
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struct futex_q *this, *next;
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int ret, op_ret, attempt = 0;
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retryfull:
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down_read(¤t->mm->mmap_sem);
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ret = get_futex_key(uaddr1, &key1);
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if (unlikely(ret != 0))
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goto out;
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ret = get_futex_key(uaddr2, &key2);
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if (unlikely(ret != 0))
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goto out;
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bh1 = hash_futex(&key1);
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bh2 = hash_futex(&key2);
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retry:
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if (bh1 < bh2)
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spin_lock(&bh1->lock);
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spin_lock(&bh2->lock);
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if (bh1 > bh2)
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spin_lock(&bh1->lock);
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op_ret = futex_atomic_op_inuser(op, (int __user *)uaddr2);
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if (unlikely(op_ret < 0)) {
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int dummy;
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spin_unlock(&bh1->lock);
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if (bh1 != bh2)
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spin_unlock(&bh2->lock);
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#ifndef CONFIG_MMU
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/* we don't get EFAULT from MMU faults if we don't have an MMU,
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* but we might get them from range checking */
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ret = op_ret;
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goto out;
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#endif
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if (unlikely(op_ret != -EFAULT)) {
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ret = op_ret;
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goto out;
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}
|
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/* futex_atomic_op_inuser needs to both read and write
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* *(int __user *)uaddr2, but we can't modify it
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* non-atomically. Therefore, if get_user below is not
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* enough, we need to handle the fault ourselves, while
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* still holding the mmap_sem. */
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if (attempt++) {
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struct vm_area_struct * vma;
|
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struct mm_struct *mm = current->mm;
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ret = -EFAULT;
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if (attempt >= 2 ||
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!(vma = find_vma(mm, uaddr2)) ||
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vma->vm_start > uaddr2 ||
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!(vma->vm_flags & VM_WRITE))
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goto out;
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|
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switch (handle_mm_fault(mm, vma, uaddr2, 1)) {
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case VM_FAULT_MINOR:
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current->min_flt++;
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break;
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case VM_FAULT_MAJOR:
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current->maj_flt++;
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break;
|
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default:
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goto out;
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}
|
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goto retry;
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}
|
|
|
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/* If we would have faulted, release mmap_sem,
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* fault it in and start all over again. */
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up_read(¤t->mm->mmap_sem);
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|
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ret = get_user(dummy, (int __user *)uaddr2);
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if (ret)
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return ret;
|
|
|
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goto retryfull;
|
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}
|
|
|
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head = &bh1->chain;
|
|
|
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list_for_each_entry_safe(this, next, head, list) {
|
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if (match_futex (&this->key, &key1)) {
|
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wake_futex(this);
|
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if (++ret >= nr_wake)
|
|
break;
|
|
}
|
|
}
|
|
|
|
if (op_ret > 0) {
|
|
head = &bh2->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(&bh1->lock);
|
|
if (bh1 != bh2)
|
|
spin_unlock(&bh2->lock);
|
|
out:
|
|
up_read(¤t->mm->mmap_sem);
|
|
return ret;
|
|
}
|
|
|
|
/*
|
|
* Requeue all waiters hashed on one physical page to another
|
|
* physical page.
|
|
*/
|
|
static int futex_requeue(unsigned long uaddr1, unsigned long uaddr2,
|
|
int nr_wake, int nr_requeue, int *valp)
|
|
{
|
|
union futex_key key1, key2;
|
|
struct futex_hash_bucket *bh1, *bh2;
|
|
struct list_head *head1;
|
|
struct futex_q *this, *next;
|
|
int ret, drop_count = 0;
|
|
|
|
retry:
|
|
down_read(¤t->mm->mmap_sem);
|
|
|
|
ret = get_futex_key(uaddr1, &key1);
|
|
if (unlikely(ret != 0))
|
|
goto out;
|
|
ret = get_futex_key(uaddr2, &key2);
|
|
if (unlikely(ret != 0))
|
|
goto out;
|
|
|
|
bh1 = hash_futex(&key1);
|
|
bh2 = hash_futex(&key2);
|
|
|
|
if (bh1 < bh2)
|
|
spin_lock(&bh1->lock);
|
|
spin_lock(&bh2->lock);
|
|
if (bh1 > bh2)
|
|
spin_lock(&bh1->lock);
|
|
|
|
if (likely(valp != NULL)) {
|
|
int curval;
|
|
|
|
ret = get_futex_value_locked(&curval, (int __user *)uaddr1);
|
|
|
|
if (unlikely(ret)) {
|
|
spin_unlock(&bh1->lock);
|
|
if (bh1 != bh2)
|
|
spin_unlock(&bh2->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, (int __user *)uaddr1);
|
|
|
|
if (!ret)
|
|
goto retry;
|
|
|
|
return ret;
|
|
}
|
|
if (curval != *valp) {
|
|
ret = -EAGAIN;
|
|
goto out_unlock;
|
|
}
|
|
}
|
|
|
|
head1 = &bh1->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;
|
|
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);
|
|
|
|
/* drop_key_refs() must be called outside the spinlocks. */
|
|
while (--drop_count >= 0)
|
|
drop_key_refs(&key1);
|
|
|
|
out:
|
|
up_read(¤t->mm->mmap_sem);
|
|
return ret;
|
|
}
|
|
|
|
/* The key must be already stored in q->key. */
|
|
static inline struct futex_hash_bucket *
|
|
queue_lock(struct futex_q *q, int fd, struct file *filp)
|
|
{
|
|
struct futex_hash_bucket *bh;
|
|
|
|
q->fd = fd;
|
|
q->filp = filp;
|
|
|
|
init_waitqueue_head(&q->waiters);
|
|
|
|
get_key_refs(&q->key);
|
|
bh = hash_futex(&q->key);
|
|
q->lock_ptr = &bh->lock;
|
|
|
|
spin_lock(&bh->lock);
|
|
return bh;
|
|
}
|
|
|
|
static inline void __queue_me(struct futex_q *q, struct futex_hash_bucket *bh)
|
|
{
|
|
list_add_tail(&q->list, &bh->chain);
|
|
spin_unlock(&bh->lock);
|
|
}
|
|
|
|
static inline void
|
|
queue_unlock(struct futex_q *q, struct futex_hash_bucket *bh)
|
|
{
|
|
spin_unlock(&bh->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 *bh;
|
|
bh = queue_lock(q, fd, filp);
|
|
__queue_me(q, bh);
|
|
}
|
|
|
|
/* 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;
|
|
|
|
/* In the common case we don't take the spinlock, which is nice. */
|
|
retry:
|
|
lock_ptr = q->lock_ptr;
|
|
if (lock_ptr != 0) {
|
|
spin_lock(lock_ptr);
|
|
/*
|
|
* q->lock_ptr can change between reading it and
|
|
* spin_lock(), causing us to take the wrong lock. This
|
|
* corrects the race condition.
|
|
*
|
|
* Reasoning goes like this: if we have the wrong lock,
|
|
* q->lock_ptr must have changed (maybe several times)
|
|
* between reading it and the spin_lock(). It can
|
|
* change again after the spin_lock() but only if it was
|
|
* already changed before the spin_lock(). It cannot,
|
|
* however, change back to the original value. Therefore
|
|
* we can detect whether we acquired the correct lock.
|
|
*/
|
|
if (unlikely(lock_ptr != q->lock_ptr)) {
|
|
spin_unlock(lock_ptr);
|
|
goto retry;
|
|
}
|
|
WARN_ON(list_empty(&q->list));
|
|
list_del(&q->list);
|
|
spin_unlock(lock_ptr);
|
|
ret = 1;
|
|
}
|
|
|
|
drop_key_refs(&q->key);
|
|
return ret;
|
|
}
|
|
|
|
static int futex_wait(unsigned long uaddr, int val, unsigned long time)
|
|
{
|
|
DECLARE_WAITQUEUE(wait, current);
|
|
int ret, curval;
|
|
struct futex_q q;
|
|
struct futex_hash_bucket *bh;
|
|
|
|
retry:
|
|
down_read(¤t->mm->mmap_sem);
|
|
|
|
ret = get_futex_key(uaddr, &q.key);
|
|
if (unlikely(ret != 0))
|
|
goto out_release_sem;
|
|
|
|
bh = queue_lock(&q, -1, NULL);
|
|
|
|
/*
|
|
* Access the page AFTER the futex is queued.
|
|
* Order is important:
|
|
*
|
|
* Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
|
|
* Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
|
|
*
|
|
* The basic logical guarantee of a futex is that it blocks ONLY
|
|
* if cond(var) is known to be true at the time of blocking, for
|
|
* any cond. If we queued after testing *uaddr, that would open
|
|
* a race condition where we could block indefinitely with
|
|
* cond(var) false, which would violate the guarantee.
|
|
*
|
|
* A consequence is that futex_wait() can return zero and absorb
|
|
* a wakeup when *uaddr != val on entry to the syscall. This is
|
|
* rare, but normal.
|
|
*
|
|
* We hold the mmap semaphore, so the mapping cannot have changed
|
|
* since we looked it up in get_futex_key.
|
|
*/
|
|
|
|
ret = get_futex_value_locked(&curval, (int __user *)uaddr);
|
|
|
|
if (unlikely(ret)) {
|
|
queue_unlock(&q, bh);
|
|
|
|
/* 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, (int __user *)uaddr);
|
|
|
|
if (!ret)
|
|
goto retry;
|
|
return ret;
|
|
}
|
|
if (curval != val) {
|
|
ret = -EWOULDBLOCK;
|
|
queue_unlock(&q, bh);
|
|
goto out_release_sem;
|
|
}
|
|
|
|
/* Only actually queue if *uaddr contained val. */
|
|
__queue_me(&q, bh);
|
|
|
|
/*
|
|
* Now the futex is queued and we have checked the data, we
|
|
* don't want to hold mmap_sem while we sleep.
|
|
*/
|
|
up_read(¤t->mm->mmap_sem);
|
|
|
|
/*
|
|
* There might have been scheduling since the queue_me(), as we
|
|
* cannot hold a spinlock across the get_user() in case it
|
|
* faults, and we cannot just set TASK_INTERRUPTIBLE state when
|
|
* queueing ourselves into the futex hash. This code thus has to
|
|
* rely on the futex_wake() code removing us from hash when it
|
|
* wakes us up.
|
|
*/
|
|
|
|
/* add_wait_queue is the barrier after __set_current_state. */
|
|
__set_current_state(TASK_INTERRUPTIBLE);
|
|
add_wait_queue(&q.waiters, &wait);
|
|
/*
|
|
* !list_empty() is safe here without any lock.
|
|
* q.lock_ptr != 0 is not safe, because of ordering against wakeup.
|
|
*/
|
|
if (likely(!list_empty(&q.list)))
|
|
time = schedule_timeout(time);
|
|
__set_current_state(TASK_RUNNING);
|
|
|
|
/*
|
|
* NOTE: we don't remove ourselves from the waitqueue because
|
|
* we are the only user of it.
|
|
*/
|
|
|
|
/* If we were woken (and unqueued), we succeeded, whatever. */
|
|
if (!unqueue_me(&q))
|
|
return 0;
|
|
if (time == 0)
|
|
return -ETIMEDOUT;
|
|
/* We expect signal_pending(current), but another thread may
|
|
* have handled it for us already. */
|
|
return -EINTR;
|
|
|
|
out_release_sem:
|
|
up_read(¤t->mm->mmap_sem);
|
|
return ret;
|
|
}
|
|
|
|
static int futex_close(struct inode *inode, struct file *filp)
|
|
{
|
|
struct futex_q *q = filp->private_data;
|
|
|
|
unqueue_me(q);
|
|
kfree(q);
|
|
return 0;
|
|
}
|
|
|
|
/* This is one-shot: once it's gone off you need a new fd */
|
|
static unsigned int futex_poll(struct file *filp,
|
|
struct poll_table_struct *wait)
|
|
{
|
|
struct futex_q *q = filp->private_data;
|
|
int ret = 0;
|
|
|
|
poll_wait(filp, &q->waiters, wait);
|
|
|
|
/*
|
|
* list_empty() is safe here without any lock.
|
|
* q->lock_ptr != 0 is not safe, because of ordering against wakeup.
|
|
*/
|
|
if (list_empty(&q->list))
|
|
ret = POLLIN | POLLRDNORM;
|
|
|
|
return ret;
|
|
}
|
|
|
|
static struct file_operations futex_fops = {
|
|
.release = futex_close,
|
|
.poll = futex_poll,
|
|
};
|
|
|
|
/*
|
|
* Signal allows caller to avoid the race which would occur if they
|
|
* set the sigio stuff up afterwards.
|
|
*/
|
|
static int futex_fd(unsigned long uaddr, int signal)
|
|
{
|
|
struct futex_q *q;
|
|
struct file *filp;
|
|
int ret, err;
|
|
|
|
ret = -EINVAL;
|
|
if (!valid_signal(signal))
|
|
goto out;
|
|
|
|
ret = get_unused_fd();
|
|
if (ret < 0)
|
|
goto out;
|
|
filp = get_empty_filp();
|
|
if (!filp) {
|
|
put_unused_fd(ret);
|
|
ret = -ENFILE;
|
|
goto out;
|
|
}
|
|
filp->f_op = &futex_fops;
|
|
filp->f_vfsmnt = mntget(futex_mnt);
|
|
filp->f_dentry = dget(futex_mnt->mnt_root);
|
|
filp->f_mapping = filp->f_dentry->d_inode->i_mapping;
|
|
|
|
if (signal) {
|
|
err = f_setown(filp, current->pid, 1);
|
|
if (err < 0) {
|
|
goto error;
|
|
}
|
|
filp->f_owner.signum = signal;
|
|
}
|
|
|
|
q = kmalloc(sizeof(*q), GFP_KERNEL);
|
|
if (!q) {
|
|
err = -ENOMEM;
|
|
goto error;
|
|
}
|
|
|
|
down_read(¤t->mm->mmap_sem);
|
|
err = get_futex_key(uaddr, &q->key);
|
|
|
|
if (unlikely(err != 0)) {
|
|
up_read(¤t->mm->mmap_sem);
|
|
kfree(q);
|
|
goto error;
|
|
}
|
|
|
|
/*
|
|
* queue_me() must be called before releasing mmap_sem, because
|
|
* key->shared.inode needs to be referenced while holding it.
|
|
*/
|
|
filp->private_data = q;
|
|
|
|
queue_me(q, ret, filp);
|
|
up_read(¤t->mm->mmap_sem);
|
|
|
|
/* Now we map fd to filp, so userspace can access it */
|
|
fd_install(ret, filp);
|
|
out:
|
|
return ret;
|
|
error:
|
|
put_unused_fd(ret);
|
|
put_filp(filp);
|
|
ret = err;
|
|
goto out;
|
|
}
|
|
|
|
/*
|
|
* Support for robust futexes: the kernel cleans up held futexes at
|
|
* thread exit time.
|
|
*
|
|
* Implementation: user-space maintains a per-thread list of locks it
|
|
* is holding. Upon do_exit(), the kernel carefully walks this list,
|
|
* and marks all locks that are owned by this thread with the
|
|
* FUTEX_OWNER_DEAD bit, and wakes up a waiter (if any). The list is
|
|
* always manipulated with the lock held, so the list is private and
|
|
* per-thread. Userspace also maintains a per-thread 'list_op_pending'
|
|
* field, to allow the kernel to clean up if the thread dies after
|
|
* acquiring the lock, but just before it could have added itself to
|
|
* the list. There can only be one such pending lock.
|
|
*/
|
|
|
|
/**
|
|
* sys_set_robust_list - set the robust-futex list head of a task
|
|
* @head: pointer to the list-head
|
|
* @len: length of the list-head, as userspace expects
|
|
*/
|
|
asmlinkage long
|
|
sys_set_robust_list(struct robust_list_head __user *head,
|
|
size_t len)
|
|
{
|
|
/*
|
|
* The kernel knows only one size for now:
|
|
*/
|
|
if (unlikely(len != sizeof(*head)))
|
|
return -EINVAL;
|
|
|
|
current->robust_list = head;
|
|
|
|
return 0;
|
|
}
|
|
|
|
/**
|
|
* sys_get_robust_list - get the robust-futex list head of a task
|
|
* @pid: pid of the process [zero for current task]
|
|
* @head_ptr: pointer to a list-head pointer, the kernel fills it in
|
|
* @len_ptr: pointer to a length field, the kernel fills in the header size
|
|
*/
|
|
asmlinkage long
|
|
sys_get_robust_list(int pid, struct robust_list_head __user **head_ptr,
|
|
size_t __user *len_ptr)
|
|
{
|
|
struct robust_list_head *head;
|
|
unsigned long ret;
|
|
|
|
if (!pid)
|
|
head = current->robust_list;
|
|
else {
|
|
struct task_struct *p;
|
|
|
|
ret = -ESRCH;
|
|
read_lock(&tasklist_lock);
|
|
p = find_task_by_pid(pid);
|
|
if (!p)
|
|
goto err_unlock;
|
|
ret = -EPERM;
|
|
if ((current->euid != p->euid) && (current->euid != p->uid) &&
|
|
!capable(CAP_SYS_PTRACE))
|
|
goto err_unlock;
|
|
head = p->robust_list;
|
|
read_unlock(&tasklist_lock);
|
|
}
|
|
|
|
if (put_user(sizeof(*head), len_ptr))
|
|
return -EFAULT;
|
|
return put_user(head, head_ptr);
|
|
|
|
err_unlock:
|
|
read_unlock(&tasklist_lock);
|
|
|
|
return ret;
|
|
}
|
|
|
|
/*
|
|
* Process a futex-list entry, check whether it's owned by the
|
|
* dying task, and do notification if so:
|
|
*/
|
|
int handle_futex_death(u32 __user *uaddr, struct task_struct *curr)
|
|
{
|
|
u32 uval;
|
|
|
|
retry:
|
|
if (get_user(uval, uaddr))
|
|
return -1;
|
|
|
|
if ((uval & FUTEX_TID_MASK) == curr->pid) {
|
|
/*
|
|
* Ok, this dying thread is truly holding a futex
|
|
* of interest. Set the OWNER_DIED bit atomically
|
|
* via cmpxchg, and if the value had FUTEX_WAITERS
|
|
* set, wake up a waiter (if any). (We have to do a
|
|
* futex_wake() even if OWNER_DIED is already set -
|
|
* to handle the rare but possible case of recursive
|
|
* thread-death.) The rest of the cleanup is done in
|
|
* userspace.
|
|
*/
|
|
if (futex_atomic_cmpxchg_inatomic(uaddr, uval,
|
|
uval | FUTEX_OWNER_DIED) != uval)
|
|
goto retry;
|
|
|
|
if (uval & FUTEX_WAITERS)
|
|
futex_wake((unsigned long)uaddr, 1);
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Walk curr->robust_list (very carefully, it's a userspace list!)
|
|
* and mark any locks found there dead, and notify any waiters.
|
|
*
|
|
* We silently return on any sign of list-walking problem.
|
|
*/
|
|
void exit_robust_list(struct task_struct *curr)
|
|
{
|
|
struct robust_list_head __user *head = curr->robust_list;
|
|
struct robust_list __user *entry, *pending;
|
|
unsigned int limit = ROBUST_LIST_LIMIT;
|
|
unsigned long futex_offset;
|
|
|
|
/*
|
|
* Fetch the list head (which was registered earlier, via
|
|
* sys_set_robust_list()):
|
|
*/
|
|
if (get_user(entry, &head->list.next))
|
|
return;
|
|
/*
|
|
* Fetch the relative futex offset:
|
|
*/
|
|
if (get_user(futex_offset, &head->futex_offset))
|
|
return;
|
|
/*
|
|
* Fetch any possibly pending lock-add first, and handle it
|
|
* if it exists:
|
|
*/
|
|
if (get_user(pending, &head->list_op_pending))
|
|
return;
|
|
if (pending)
|
|
handle_futex_death((void *)pending + futex_offset, curr);
|
|
|
|
while (entry != &head->list) {
|
|
/*
|
|
* A pending lock might already be on the list, so
|
|
* dont process it twice:
|
|
*/
|
|
if (entry != pending)
|
|
if (handle_futex_death((void *)entry + futex_offset,
|
|
curr))
|
|
return;
|
|
/*
|
|
* Fetch the next entry in the list:
|
|
*/
|
|
if (get_user(entry, &entry->next))
|
|
return;
|
|
/*
|
|
* Avoid excessively long or circular lists:
|
|
*/
|
|
if (!--limit)
|
|
break;
|
|
|
|
cond_resched();
|
|
}
|
|
}
|
|
|
|
long do_futex(unsigned long uaddr, int op, int val, unsigned long timeout,
|
|
unsigned long uaddr2, int val2, int val3)
|
|
{
|
|
int ret;
|
|
|
|
switch (op) {
|
|
case FUTEX_WAIT:
|
|
ret = futex_wait(uaddr, val, timeout);
|
|
break;
|
|
case FUTEX_WAKE:
|
|
ret = futex_wake(uaddr, val);
|
|
break;
|
|
case FUTEX_FD:
|
|
/* non-zero val means F_SETOWN(getpid()) & F_SETSIG(val) */
|
|
ret = futex_fd(uaddr, val);
|
|
break;
|
|
case FUTEX_REQUEUE:
|
|
ret = futex_requeue(uaddr, uaddr2, val, val2, NULL);
|
|
break;
|
|
case FUTEX_CMP_REQUEUE:
|
|
ret = futex_requeue(uaddr, uaddr2, val, val2, &val3);
|
|
break;
|
|
case FUTEX_WAKE_OP:
|
|
ret = futex_wake_op(uaddr, uaddr2, val, val2, val3);
|
|
break;
|
|
default:
|
|
ret = -ENOSYS;
|
|
}
|
|
return ret;
|
|
}
|
|
|
|
|
|
asmlinkage long sys_futex(u32 __user *uaddr, int op, int val,
|
|
struct timespec __user *utime, u32 __user *uaddr2,
|
|
int val3)
|
|
{
|
|
struct timespec t;
|
|
unsigned long timeout = MAX_SCHEDULE_TIMEOUT;
|
|
int val2 = 0;
|
|
|
|
if (utime && (op == FUTEX_WAIT)) {
|
|
if (copy_from_user(&t, utime, sizeof(t)) != 0)
|
|
return -EFAULT;
|
|
if (!timespec_valid(&t))
|
|
return -EINVAL;
|
|
timeout = timespec_to_jiffies(&t) + 1;
|
|
}
|
|
/*
|
|
* requeue parameter in 'utime' if op == FUTEX_REQUEUE.
|
|
*/
|
|
if (op >= FUTEX_REQUEUE)
|
|
val2 = (int) (unsigned long) utime;
|
|
|
|
return do_futex((unsigned long)uaddr, op, val, timeout,
|
|
(unsigned long)uaddr2, val2, val3);
|
|
}
|
|
|
|
static int futexfs_get_sb(struct file_system_type *fs_type,
|
|
int flags, const char *dev_name, void *data,
|
|
struct vfsmount *mnt)
|
|
{
|
|
return get_sb_pseudo(fs_type, "futex", NULL, 0xBAD1DEA, mnt);
|
|
}
|
|
|
|
static struct file_system_type futex_fs_type = {
|
|
.name = "futexfs",
|
|
.get_sb = futexfs_get_sb,
|
|
.kill_sb = kill_anon_super,
|
|
};
|
|
|
|
static int __init init(void)
|
|
{
|
|
unsigned int i;
|
|
|
|
register_filesystem(&futex_fs_type);
|
|
futex_mnt = kern_mount(&futex_fs_type);
|
|
|
|
for (i = 0; i < ARRAY_SIZE(futex_queues); i++) {
|
|
INIT_LIST_HEAD(&futex_queues[i].chain);
|
|
spin_lock_init(&futex_queues[i].lock);
|
|
}
|
|
return 0;
|
|
}
|
|
__initcall(init);
|