From: Andrew Morton <akpm@linux-foundation.org>

Cc: Eric Dumazet <dada1@cosmosbay.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 drivers/lguest/io.c |   21 ++++++++++++---------
 1 files changed, 12 insertions(+), 9 deletions(-)

diff -puN drivers/lguest/io.c~lguest-the-host-code-vs-futex-new-private-futexes drivers/lguest/io.c
--- a/drivers/lguest/io.c~lguest-the-host-code-vs-futex-new-private-futexes
+++ a/drivers/lguest/io.c
@@ -102,13 +102,14 @@ int bind_dma(struct lguest *lg,
 	unsigned int i;
 	int ret = 0;
 	union futex_key key;
+	struct rw_semaphore *fshared = &current->mm->mmap_sem;
 
 	if (interrupt >= LGUEST_IRQS)
 		return 0;
 
 	mutex_lock(&lguest_lock);
-	down_read(&current->mm->mmap_sem);
-	if (get_futex_key((u32 __user *)ukey, sizeof(u32), &key) != 0) {
+	down_read(fshared);
+	if (get_futex_key((u32 __user *)ukey, sizeof(u32), fshared, &key)) {
 		kill_guest(lg, "bad dma key %#lx", ukey);
 		goto unlock;
 	}
@@ -134,7 +135,7 @@ int bind_dma(struct lguest *lg,
 	}
 	drop_futex_key_refs(&key);
 unlock:
- 	up_read(&current->mm->mmap_sem);
+ 	up_read(fshared);
 	mutex_unlock(&lguest_lock);
 	return ret;
 }
@@ -307,11 +308,12 @@ void send_dma(struct lguest *lg, unsigne
 {
 	union futex_key key;
 	int empty = 0;
+	struct rw_semaphore *fshared = &current->mm->mmap_sem;
 
 again:
 	mutex_lock(&lguest_lock);
-	down_read(&current->mm->mmap_sem);
-	if (get_futex_key((u32 __user *)ukey, sizeof(u32), &key) != 0) {
+	down_read(fshared);
+	if (get_futex_key((u32 __user *)ukey, sizeof(u32), fshared, &key)) {
 		kill_guest(lg, "bad sending DMA key");
 		goto unlock;
 	}
@@ -342,7 +344,7 @@ again:
 		lg->pending_key = ukey;
 	}
 unlock:
-	up_read(&current->mm->mmap_sem);
+	up_read(fshared);
 	mutex_unlock(&lguest_lock);
 }
 
@@ -382,10 +384,11 @@ unsigned long get_dma_buffer(struct lgue
 	unsigned long ret = 0;
 	union futex_key key;
 	struct lguest_dma_info *i;
+	struct rw_semaphore *fshared = &current->mm->mmap_sem;
 
 	mutex_lock(&lguest_lock);
-	down_read(&current->mm->mmap_sem);
-	if (get_futex_key((u32 __user *)ukey, sizeof(u32), &key) != 0) {
+	down_read(fshared);
+	if (get_futex_key((u32 __user *)ukey, sizeof(u32), fshared, &key)) {
 		kill_guest(lg, "bad registered DMA buffer");
 		goto unlock;
 	}
@@ -405,7 +408,7 @@ unsigned long get_dma_buffer(struct lgue
 		}
 	}
 unlock:
-	up_read(&current->mm->mmap_sem);
+	up_read(fshared);
 	mutex_unlock(&lguest_lock);
 	return ret;
 }
_