Add lock_page_killable

This routine is like lock_page, but can be interrupted by a fatal signal

Signed-off-by: Matthew Wilcox <willy@linux.intel.com>

mm/filemap.c

@@ -173,6 +173,12 @@ static int sync_page(void *word)
 	return 0;
 }
 
+static int sync_page_killable(void *word)
+{
+	sync_page(word);
+	return fatal_signal_pending(current) ? -EINTR : 0;
+}
+
 /**
  * __filemap_fdatawrite_range - start writeback on mapping dirty pages in range
  * @mapping:	address space structure to write
@@ -577,6 +583,14 @@ void fastcall __lock_page(struct page *page)
 }
 EXPORT_SYMBOL(__lock_page);
 
+int fastcall __lock_page_killable(struct page *page)
+{
+	DEFINE_WAIT_BIT(wait, &page->flags, PG_locked);
+
+	return __wait_on_bit_lock(page_waitqueue(page), &wait,
+					sync_page_killable, TASK_KILLABLE);
+}
+
 /*
  * Variant of lock_page that does not require the caller to hold a reference
  * on the page's mapping.