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futex: Restore one of the fast paths eliminated by 38d47c1b70

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This improves futex performance until our user-space code is fixed to use
FUTEX_PRIVATE_FLAG for non-shared futexes.

Signed-off-by: Arve Hjønnevåg <arve@android.com>
This commit is contained in:
Arve Hjønnevåg
2009-06-09 20:21:44 -07:00
committed by Colin Cross
parent 85a450f980
commit cb93471ed5
1 changed files with 32 additions and 0 deletions
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32
kernel/futex.c
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@@ -220,6 +220,7 @@ get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key)
struct mm_struct *mm = current->mm;
struct page *page;
int err;
struct vm_area_struct *vma;
/*
* The futex address must be "naturally" aligned.
@@ -245,6 +246,37 @@ get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key)
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;
get_futex_key_refs(key);
return 0;
}
again:
err = get_user_pages_fast(address, 1, 1, &page);
if (err < 0)