Use lock_page_killable

Replacing lock_page with lock_page_killable in do_generic_mapping_read()
allows us to kill `cat' of a file on an NFS-mounted filesystem

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

mm/filemap.c

@@ -982,7 +982,8 @@ page_ok:
 
 page_not_up_to_date:
 		/* Get exclusive access to the page ... */
-		lock_page(page);
+		if (lock_page_killable(page))
+			goto readpage_eio;
 
 		/* Did it get truncated before we got the lock? */
 		if (!page->mapping) {
@@ -1010,7 +1011,8 @@ readpage:
 		}
 
 		if (!PageUptodate(page)) {
-			lock_page(page);
+			if (lock_page_killable(page))
+				goto readpage_eio;
 			if (!PageUptodate(page)) {
 				if (page->mapping == NULL) {
 					/*
@@ -1021,15 +1023,16 @@ readpage:
 					goto find_page;
 				}
 				unlock_page(page);
-				error = -EIO;
 				shrink_readahead_size_eio(filp, ra);
-				goto readpage_error;
+				goto readpage_eio;
 			}
 			unlock_page(page);
 		}
 
 		goto page_ok;
 
+readpage_eio:
+		error = -EIO;
 readpage_error:
 		/* UHHUH! A synchronous read error occurred. Report it */
 		desc->error = error;