[PATCH] FRV: Make futex code compilable on nommu [try #2]

Make the futex code compilable and usable on NOMMU by making the attempt to
handle page faults conditional on CONFIG_MMU.  If this is not enabled, then
we can assume that EFAULT returned from futex_atomic_op_inuser() is not
recoverable, and that the address lies outside of valid memory.

handle_mm_fault() is made to BUG if called on NOMMU without attempting to
invoke the actual handler (__handle_mm_fault).
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/linux/mm.h

@@ -717,12 +717,28 @@ extern int vmtruncate(struct inode * inode, loff_t offset);
 extern int vmtruncate_range(struct inode * inode, loff_t offset, loff_t end);
 extern int install_page(struct mm_struct *mm, struct vm_area_struct *vma, unsigned long addr, struct page *page, pgprot_t prot);
 extern int install_file_pte(struct mm_struct *mm, struct vm_area_struct *vma, unsigned long addr, unsigned long pgoff, pgprot_t prot);
-extern int __handle_mm_fault(struct mm_struct *mm,struct vm_area_struct *vma, unsigned long address, int write_access);
 
-static inline int handle_mm_fault(struct mm_struct *mm, struct vm_area_struct *vma, unsigned long address, int write_access)
+#ifdef CONFIG_MMU
+extern int __handle_mm_fault(struct mm_struct *mm,struct vm_area_struct *vma,
+			unsigned long address, int write_access);
+
+static inline int handle_mm_fault(struct mm_struct *mm,
+			struct vm_area_struct *vma, unsigned long address,
+			int write_access)
 {
-	return __handle_mm_fault(mm, vma, address, write_access) & (~VM_FAULT_WRITE);
+	return __handle_mm_fault(mm, vma, address, write_access) &
+				(~VM_FAULT_WRITE);
 }
+#else
+static inline int handle_mm_fault(struct mm_struct *mm,
+			struct vm_area_struct *vma, unsigned long address,
+			int write_access)
+{
+	/* should never happen if there's no MMU */
+	BUG();
+	return VM_FAULT_SIGBUS;
+}
+#endif
 
 extern int make_pages_present(unsigned long addr, unsigned long end);
 extern int access_process_vm(struct task_struct *tsk, unsigned long addr, void *buf, int len, int write);

kernel/futex.c

@@ -356,6 +356,13 @@ retry:
 		if (bh1 != bh2)
 			spin_unlock(&bh2->lock);
 
+#ifndef CONFIG_MMU
+		/* we don't get EFAULT from MMU faults if we don't have an MMU,
+		 * but we might get them from range checking */
+		ret = op_ret;
+		goto out;
+#endif
+
 		if (unlikely(op_ret != -EFAULT)) {
 			ret = op_ret;
 			goto out;