futex: use fast_gup()

Change the get_user_pages() call with fast_gup() which doesn't require holding
the mmap_sem thereby removing the mmap_sem from all fast paths.

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>

diff --git a/kernel/futex.c b/kernel/futex.c
index 6a72668..facf17d 100644 (file)
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -232,9 +232,7 @@ static int get_futex_key(u32 __user *uaddr, struct rw_semaphore *fshared,
        }
 
 again:
-       down_read(&mm->mmap_sem);
-       err = get_user_pages(current, mm, address, 1, 0, 0, &page, NULL);
-       up_read(&mm->mmap_sem);
+       err = get_user_pages_fast(address, 1, 0, &page);
        if (err < 0)
                return err;