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futex: rely on get_user_pages() for shared futexes
On the way of getting rid of the mmap_sem requirement for shared futexes, start by relying on get_user_pages(). Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Acked-by: Nick Piggin <nickpiggin@yahoo.com.au> Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra
Ingo Molnar
parent
94aca1dac6
commit
38d47c1b70
@ -164,6 +164,8 @@ union futex_key {
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} both;
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};
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#define FUTEX_KEY_INIT (union futex_key) { .both = { .ptr = NULL } }
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#ifdef CONFIG_FUTEX
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extern void exit_robust_list(struct task_struct *curr);
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extern void exit_pi_state_list(struct task_struct *curr);
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162
kernel/futex.c
162
kernel/futex.c
@ -161,6 +161,45 @@ static inline int match_futex(union futex_key *key1, union futex_key *key2)
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&& key1->both.offset == key2->both.offset);
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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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*/
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static void get_futex_key_refs(union futex_key *key)
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{
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if (!key->both.ptr)
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return;
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switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
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case FUT_OFF_INODE:
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atomic_inc(&key->shared.inode->i_count);
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break;
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case FUT_OFF_MMSHARED:
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atomic_inc(&key->private.mm->mm_count);
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break;
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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_futex_key_refs(union futex_key *key)
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{
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if (!key->both.ptr)
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return;
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switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
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case FUT_OFF_INODE:
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iput(key->shared.inode);
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break;
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case FUT_OFF_MMSHARED:
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mmdrop(key->private.mm);
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break;
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}
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}
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/**
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* get_futex_key - Get parameters which are the keys for a futex.
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* @uaddr: virtual address of the futex
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@ -184,7 +223,6 @@ static int get_futex_key(u32 __user *uaddr, struct rw_semaphore *fshared,
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{
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unsigned long address = (unsigned long)uaddr;
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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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@ -210,98 +248,47 @@ static int get_futex_key(u32 __user *uaddr, struct rw_semaphore *fshared,
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key->private.address = address;
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return 0;
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}
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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, address);
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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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again:
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err = get_user_pages(current, mm, address, 1, 0, 0, &page, NULL);
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if (err < 0)
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return err;
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lock_page(page);
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if (!page->mapping) {
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unlock_page(page);
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put_page(page);
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goto again;
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}
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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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* the object not the particular process.
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*/
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if (likely(!(vma->vm_flags & VM_MAYSHARE))) {
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key->both.offset |= FUT_OFF_MMSHARED; /* reference taken on mm */
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if (PageAnon(page)) {
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key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
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key->private.mm = mm;
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key->private.address = address;
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return 0;
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} else {
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key->both.offset |= FUT_OFF_INODE; /* inode-based key */
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key->shared.inode = page->mapping->host;
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key->shared.pgoff = page->index;
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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_path.dentry->d_inode;
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key->both.offset |= FUT_OFF_INODE; /* inode-based key. */
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if (likely(!(vma->vm_flags & VM_NONLINEAR))) {
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key->shared.pgoff = (((address - 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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get_futex_key_refs(key);
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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, address, 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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unlock_page(page);
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put_page(page);
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return 0;
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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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*/
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static void get_futex_key_refs(union futex_key *key)
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static inline
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void put_futex_key(struct rw_semaphore *fshared, union futex_key *key)
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{
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if (key->both.ptr == NULL)
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return;
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switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
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case FUT_OFF_INODE:
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atomic_inc(&key->shared.inode->i_count);
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break;
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case FUT_OFF_MMSHARED:
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atomic_inc(&key->private.mm->mm_count);
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break;
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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_futex_key_refs(union futex_key *key)
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{
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if (!key->both.ptr)
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return;
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switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
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case FUT_OFF_INODE:
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iput(key->shared.inode);
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break;
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case FUT_OFF_MMSHARED:
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mmdrop(key->private.mm);
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break;
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}
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drop_futex_key_refs(key);
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}
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static u32 cmpxchg_futex_value_locked(u32 __user *uaddr, u32 uval, u32 newval)
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@ -385,6 +372,7 @@ static int refill_pi_state_cache(void)
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/* pi_mutex gets initialized later */
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pi_state->owner = NULL;
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atomic_set(&pi_state->refcount, 1);
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pi_state->key = FUTEX_KEY_INIT;
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current->pi_state_cache = pi_state;
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@ -462,7 +450,7 @@ void exit_pi_state_list(struct task_struct *curr)
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struct list_head *next, *head = &curr->pi_state_list;
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struct futex_pi_state *pi_state;
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struct futex_hash_bucket *hb;
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union futex_key key;
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union futex_key key = FUTEX_KEY_INIT;
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if (!futex_cmpxchg_enabled)
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return;
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@ -725,7 +713,7 @@ static int futex_wake(u32 __user *uaddr, struct rw_semaphore *fshared,
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struct futex_hash_bucket *hb;
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struct futex_q *this, *next;
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struct plist_head *head;
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union futex_key key;
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union futex_key key = FUTEX_KEY_INIT;
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int ret;
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if (!bitset)
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@ -760,6 +748,7 @@ static int futex_wake(u32 __user *uaddr, struct rw_semaphore *fshared,
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spin_unlock(&hb->lock);
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out:
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put_futex_key(fshared, &key);
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futex_unlock_mm(fshared);
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return ret;
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}
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@ -773,7 +762,7 @@ futex_wake_op(u32 __user *uaddr1, struct rw_semaphore *fshared,
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u32 __user *uaddr2,
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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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union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
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struct futex_hash_bucket *hb1, *hb2;
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struct plist_head *head;
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struct futex_q *this, *next;
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@ -873,6 +862,8 @@ retry:
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if (hb1 != hb2)
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spin_unlock(&hb2->lock);
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out:
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put_futex_key(fshared, &key2);
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put_futex_key(fshared, &key1);
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futex_unlock_mm(fshared);
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return ret;
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@ -886,7 +877,7 @@ static int futex_requeue(u32 __user *uaddr1, struct rw_semaphore *fshared,
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u32 __user *uaddr2,
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int nr_wake, int nr_requeue, u32 *cmpval)
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{
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union futex_key key1, key2;
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union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
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struct futex_hash_bucket *hb1, *hb2;
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struct plist_head *head1;
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struct futex_q *this, *next;
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@ -974,6 +965,8 @@ out_unlock:
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drop_futex_key_refs(&key1);
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out:
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put_futex_key(fshared, &key2);
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put_futex_key(fshared, &key1);
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futex_unlock_mm(fshared);
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return ret;
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}
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@ -1220,6 +1213,7 @@ static int futex_wait(u32 __user *uaddr, struct rw_semaphore *fshared,
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retry:
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futex_lock_mm(fshared);
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q.key = FUTEX_KEY_INIT;
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ret = get_futex_key(uaddr, fshared, &q.key);
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if (unlikely(ret != 0))
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goto out_release_sem;
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@ -1360,6 +1354,7 @@ static int futex_wait(u32 __user *uaddr, struct rw_semaphore *fshared,
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queue_unlock(&q, hb);
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out_release_sem:
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put_futex_key(fshared, &q.key);
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futex_unlock_mm(fshared);
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return ret;
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}
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@ -1411,6 +1406,7 @@ static int futex_lock_pi(u32 __user *uaddr, struct rw_semaphore *fshared,
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retry:
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futex_lock_mm(fshared);
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q.key = FUTEX_KEY_INIT;
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ret = get_futex_key(uaddr, fshared, &q.key);
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if (unlikely(ret != 0))
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goto out_release_sem;
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@ -1625,6 +1621,7 @@ static int futex_lock_pi(u32 __user *uaddr, struct rw_semaphore *fshared,
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queue_unlock(&q, hb);
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out_release_sem:
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put_futex_key(fshared, &q.key);
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futex_unlock_mm(fshared);
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if (to)
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destroy_hrtimer_on_stack(&to->timer);
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@ -1671,7 +1668,7 @@ static int futex_unlock_pi(u32 __user *uaddr, struct rw_semaphore *fshared)
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struct futex_q *this, *next;
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u32 uval;
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struct plist_head *head;
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union futex_key key;
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union futex_key key = FUTEX_KEY_INIT;
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int ret, attempt = 0;
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retry:
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@ -1744,6 +1741,7 @@ retry_unlocked:
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out_unlock:
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spin_unlock(&hb->lock);
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out:
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put_futex_key(fshared, &key);
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futex_unlock_mm(fshared);
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return ret;
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