mn10300/mm/fault.c: Port OOM changes to do_page_fault

Commit d065bd810b6deb67d4897a14bfe21f8eb526ba99
(mm: retry page fault when blocking on disk transfer) and
commit 37b23e0525d393d48a7d59f870b3bc061a30ccdb
(x86,mm: make pagefault killable)

The above commits introduced changes into the x86 pagefault handler
for making the page fault handler retryable as well as killable.

These changes reduce the mmap_sem hold time, which is crucial
during OOM killer invocation.

Port these changes to mn10300.

Signed-off-by: Kautuk Consul <consul.kautuk@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>

arch/mn10300/mm/fault.c

@@ -123,7 +123,8 @@ asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long fault_code,
 	struct mm_struct *mm;
 	unsigned long page;
 	siginfo_t info;
-	int write, fault;
+	int fault;
+	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
 
 #ifdef CONFIG_GDBSTUB
 	/* handle GDB stub causing a fault */
@@ -170,6 +171,7 @@ asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long fault_code,
 	if (in_atomic() || !mm)
 		goto no_context;
 
+retry:
 	down_read(&mm->mmap_sem);
 
 	vma = find_vma(mm, address);
@@ -220,7 +222,6 @@ asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long fault_code,
  */
 good_area:
 	info.si_code = SEGV_ACCERR;
-	write = 0;
 	switch (fault_code & (MMUFCR_xFC_PGINVAL|MMUFCR_xFC_TYPE)) {
 	default:	/* 3: write, present */
 	case MMUFCR_xFC_TYPE_WRITE:
@@ -232,7 +233,7 @@ good_area:
 	case MMUFCR_xFC_PGINVAL | MMUFCR_xFC_TYPE_WRITE:
 		if (!(vma->vm_flags & VM_WRITE))
 			goto bad_area;
-		write++;
+		flags |= FAULT_FLAG_WRITE;
 		break;
 
 		/* read from protected page */
@@ -251,7 +252,11 @@ good_area:
 	 * make sure we exit gracefully rather than endlessly redo
 	 * the fault.
 	 */
-	fault = handle_mm_fault(mm, vma, address, write ? FAULT_FLAG_WRITE : 0);
+	fault = handle_mm_fault(mm, vma, address, flags);
+
+	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+		return;
+
 	if (unlikely(fault & VM_FAULT_ERROR)) {
 		if (fault & VM_FAULT_OOM)
 			goto out_of_memory;
@@ -259,10 +264,22 @@ good_area:
 			goto do_sigbus;
 		BUG();
 	}
-	if (fault & VM_FAULT_MAJOR)
-		current->maj_flt++;
-	else
-		current->min_flt++;
+	if (flags & FAULT_FLAG_ALLOW_RETRY) {
+		if (fault & VM_FAULT_MAJOR)
+			current->maj_flt++;
+		else
+			current->min_flt++;
+		if (fault & VM_FAULT_RETRY) {
+			flags &= ~FAULT_FLAG_ALLOW_RETRY;
+
+			 /* No need to up_read(&mm->mmap_sem) as we would
+			 * have already released it in __lock_page_or_retry
+			 * in mm/filemap.c.
+			 */
+
+			goto retry;
+		}
+	}
 
 	up_read(&mm->mmap_sem);
 	return;