[PATCH] Don't map random pages if swapoff errors

[Alexey Dobriyan <adobriyan@openvz.org>]

From: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>

If read failed we cannot map not-uptodate page to user space.
Actually, we are in serious troubles, we do not even know what
process to kill. So, the only variant remains: to stop swapoff()
and allow someone to kill processes to zap invalid pages.

Signed-off-by: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
Signed-off-by: Alexey Dobriyan <adobriyan@openvz.org>
---

 mm/swapfile.c |   13 +++++++++++++
 1 file changed, 13 insertions(+)

--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -766,6 +766,19 @@ static int try_to_unuse(unsigned int typ
 		lock_page(page);
 		wait_on_page_writeback(page);
 
+		/* If read failed we cannot map not-uptodate page to
+		 * user space. Actually, we are in serious troubles,
+		 * we do not even know what process to kill. So, the only
+		 * variant remains: to stop swapoff() and allow someone
+		 * to kill processes to zap invalid pages.
+		 */
+		if (unlikely(!PageUptodate(page))) {
+			unlock_page(page);
+			page_cache_release(page);
+			retval = -EIO;
+			break;
+		}
+
 		/*
 		 * Remove all references to entry.
 		 * Whenever we reach init_mm, there's no address space