[S390] don't call handle_mm_fault() if in an atomic context.

There are several places in the futex code where a spin_lock is held
and still uaccesses happen. Deadlocks are avoided by increasing the
preempt count. The pagefault handler will then not take any locks
but will immediately search the fixup tables.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/lib/uaccess_pt.c

@@ -8,6 +8,7 @@
  */
 
 #include <linux/errno.h>
+#include <linux/hardirq.h>
 #include <linux/mm.h>
 #include <asm/uaccess.h>
 #include <asm/futex.h>
@@ -18,6 +19,8 @@ static inline int __handle_fault(struct mm_struct *mm, unsigned long address,
 	struct vm_area_struct *vma;
 	int ret = -EFAULT;
 
+	if (in_atomic())
+		return ret;
 	down_read(&mm->mmap_sem);
 	vma = find_vma(mm, address);
 	if (unlikely(!vma))

arch/s390/lib/uaccess_std.c

@@ -258,8 +258,6 @@ int futex_atomic_op(int op, int __user *uaddr, int oparg, int *old)
 {
 	int oldval = 0, newval, ret;
 
-	pagefault_disable();
-
 	switch (op) {
 	case FUTEX_OP_SET:
 		__futex_atomic_op("lr %2,%5\n",
@@ -284,7 +282,6 @@ int futex_atomic_op(int op, int __user *uaddr, int oparg, int *old)
 	default:
 		ret = -ENOSYS;
 	}
-	pagefault_enable();
 	*old = oldval;
 	return ret;
 }

include/asm-s390/futex.h

@@ -4,8 +4,8 @@
 #ifdef __KERNEL__
 
 #include <linux/futex.h>
+#include <linux/uaccess.h>
 #include <asm/errno.h>
-#include <asm/uaccess.h>
 
 static inline int futex_atomic_op_inuser (int encoded_op, int __user *uaddr)
 {
@@ -21,7 +21,9 @@ static inline int futex_atomic_op_inuser (int encoded_op, int __user *uaddr)
 	if (! access_ok (VERIFY_WRITE, uaddr, sizeof(int)))
 		return -EFAULT;
 
+	pagefault_disable();
 	ret = uaccess.futex_atomic_op(op, uaddr, oparg, &oldval);
+	pagefault_enable();
 
 	if (!ret) {
 		switch (cmp) {