From cb93471ed5d924b6efdfe5d0215668a9b4b91c21 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Arve=20Hj=C3=B8nnev=C3=A5g?= Date: Tue, 9 Jun 2009 20:21:44 -0700 Subject: [PATCH] futex: Restore one of the fast paths eliminated by 38d47c1b7075bd7ec3881141bb3629da58f88dab MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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 --- kernel/futex.c | 32 ++++++++++++++++++++++++++++++++ 1 file changed, 32 insertions(+) diff --git a/kernel/futex.c b/kernel/futex.c index 6a3a5fa1526d..257db2460ab8 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -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) -- 2.34.1